Management strategies for a borehole resin production system in slash pine


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Management strategies for a borehole resin production system in slash pine
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vi, 109 leaves : ill. ; 29 cm.
Hodges, Alan W ( Alan Wade ), 1959-
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Agricultural and Biological Engineering thesis, Ph. D
Dissertations, Academic -- Agricultural and Biological Engineering -- UF
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Thesis (Ph. D.)--University of Florida, 1995.
Includes bibliographical references (leaves 102-108).
Statement of Responsibility:
by Alan W. Hodges.
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University of Florida
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oclc - 33430248
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The contributions of many persons made this work possible over a period of six

years. Grady Williams, retired Georgia Forestry Commission, originally discovered the

technique of borehole resin production, and worked continually with the author in all

aspects of its development. Robert McReynolds, retired USDA Forest Service, assisted

with research on many occasions. Fred Allen, former Research Director of the Georgia

Forestry Commission, provided continuing financial support for the project. Pierre

deLarosiere of Navstoc Inc. sponsored efforts in mechanization of the borehole tapping

system. Jim Gillis, Jr. and Joyce Lamb of The American Turpentine Farmers

Association administered research contracts for the project. Personnel of the Georgia

Forestry Commission who helped with field work for the project include Wes Hartley,

Ed Herbert, Red Castleman, Christopher Stuckey and David Wesley. Landowners

providing study sites were Amos Sumner and Clark Smith. The University of Florida

School of Forest Resources and Conservation allowed use of experimental plots at

Austin Cary Forest in 1994. Akzo Coatings and Drew Forest Chemicals Laboratory

provided laboratory services. Supervisory committee members for earlier related work

on a masters thesis project at the University of Florida were Drs. W. David Shoup,

Larry Shaw, and Susan Kossuth.


ACKNOW LEDGEMENTS ........................................ ii

A abstract ..... ........................... ... ............... v

INTRODUCTION ............................................. 1
The Borehole Resin Production System ........................ 1
Ecology and Natural History of the Pine Resin System ............. 5
Anatomy and Physiology of Oleoresin Production ................. 6
Economics of Commercial Resin Production and Utilization .......... 8
Technology Development in Gum Resin Production Systems ......... 9
Productivity and Behavior of Oleoresin Production Systems ........ 11
Related Tree Extractive Production Systems .................. 14

PRODUCTION SYSTEM ................................. 17

Fundamental Laws Governing Resin System Behavior ............. 23
A Basal Area Representation of Oleoresin Storage and Flow ........ 28
Management Related System Factors and Experimental Treatments ... 30

Research Sites and Plots ................................. 33
Borehole Treatment Procedures ............................ 34
Yield Measurements and Tree Observations .................. 39
Design of Borehole Tapping Experiments ..................... 40
Compartment Model Area Calculations ...................... 43
Increment Core Analyses for Borehole-Tapped Trees ............ 44
Physico-Chemical Analysis of Oleoresin Produced by Borehole
Tapping ....................................... 46
Data Analysis Procedures ................................ 47

Effects of Resource Quality ............................... 49
Species ........................................ 49
Sites ..... ......................... .. .... ... .. 50
Tree Size ....................................... 51
Borehole Tapping Treatment Effects ........................ 52
Borehole Diameter and Depth ........................ 52
Hole Orientation .................................. 55
Spacing Among Clustered Boreholes .................. 56
Chemical/Biological Treatment Effects ................. 59
Effects of Collection Container Type ....................... 61
Effects of Time of Year .................................. 62
Yields for A Second Year of Production ..................... 64
Resin Flow Rates Over Time Since Treatment ................. 65
Yields by Compartment Area .............................. 68

Analysis of Tree Tapping Intensity ......................... 69
Response Surface Analysis and Treatment Optimization ........... 74
Productivity Comparisons With Traditional Systems .............. 75

Effects on Tree Growth ................................. 77
Tree Stress Effects ..................................... 78
Deposition of Extractives ................................ 80
Physico-Chemical Properties of Oleoresin .................... 83

Need for Mechanization of Borehole Tapping .................. 85
Mechanized System Design Concepts ....................... 86
Mechanized Drilling System Construction .................... 89
Spout-Bag Collection System .............................. 92
Tests of the Mechanized Borehole Tapping System .............. 94
Lifecycle Cost Analysis of the Mechanized Drilling Machine ........ 97

DISCUSSION AND CONCLUSIONS .............................. 99

LITERATURE CITED ......................................... 102

BIOGRAPHICAL SKETCH ..................................... 109

Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy



Alan W. Hodges

May, 1995

Chairman: John Wayne Mishoe
Major Department: Agricultural and Biological Engineering

A new process is described for production of oleoresin from slash pine

(Pinus elliottii) by means of borehole wounds to the tree's xylem. Advantages of

this process over conventional gum resin production methods include higher labor

productivity, improved product quality, reduced tree stress, and reduced insect pest

problems. Resin yields averaged 650 g per borehole, or nearly 1.7 kg per tree with

multiple boreholes, in tapping experiments conducted from 1991 to 1994 in Florida

and Georgia, USA. Borehole yields were generally more variable than for

conventional gum resin production. Yields were significantly affected by tree size,

and experimental treatments for borehole diameter, depth, number, spacing,

horizontal and vertical orientation and spacing, chemical stimulants, and collection

container type. Yields were highest for borehole treatments during the midsummer

period (August), but did not differ at other times of year. Resin flow from a single

tapping treatment continued over a period of several months, and was well-

described by a negative exponential function of time, with 90 percent of cumulative

seasonal flow attained at 120 days after treatment. Tree growth rates were not

measurably altered by borehole tapping. A systems model of borehole resin

production was conceptualized in terms of closed-channel hydraulic flow under

hydrostatic pressure gradients, and a system architecture of the resin duct network

that gives rise to predictable patterns of oleoresin drainage. Tree basal area was

used as an indicator of preformed oleoresin storage capacity, and resin yields per

unit cross-sectional area of the tree stem were modeled as a function of tapping

treatment extent and intensity. Management strategies and borehole treatments

were designed to maximize borehole yields by controlling tapping treatment

intensities. At the optimal treatment level, predicted yields ranged from 1520 to

3100 g for trees 23 to 37 cm dbh, respectively. A mechanized borehole production

system was developed, including a mobile multiple-spindle drilling system, and a

spout-bag container apparatus. Field tests of the mechanized system operation

demonstrated a capacity of 59 trees per hour, representing a 50 percent increase in

labor productivity over non-mechanized systems.


The Borehole Resin Production System

In 1990, a new technique for producing oleoresin from living Slash pine trees

(Pinus elliottil) was discovered by longtime gum resin farmers in Georgia USA, and

subsequently developed by researchers (Hodges and Williams, 1993). The borehole

tapping process essentially involves drilling holes into the xylem to open resin ducts

and provide a pathway for their drainage into a closed collection device. Various

commercial and experimental devices have been described for collecting resin from

small punch wounds to the bark, essentially as a bark-chipping treatment (Low and

Abdul Razak, 1985; Ostrum, 1946; Kraus, 1965); however, no previous reports of

a borehole tree exudate production system have appeared in the English literature.

A typical borehole treatment pattern for a tree is depicted in Figure 1.1.

The borehole treatment process consists of drilling several holes 2.5 cm in diameter

by 7.6 to 17.8 cm deep (1 by 3 to 7 inches). Boreholes are placed approximately

10 cm above ground level, in trees at least 15 cm diameter at breast height (dbh).

Chemical treatments of sulfuric acid (H2SO4) and CEPA are sprayed inside boreholes

to improve yields, as with conventional open-face tapping methods. Resin flows

from the borehole into an attached collection device, beginning immediately after

treatment, and continuing for a period of several months. The prolonged flow from

boreholes is a key feature of this system. The borehole system represents a logical

extension of the evolutionary trend in gum resin production systems toward

internalization of the wounding
Equal Circumferential Spacing, Radial Alignment
process. Originally, the

production system concept was

demonstrated as an

atmospherically sealed collecting s i m
2,54 cm dia
resin with 2-liter PET bottles

screwed directly into boreholes

using their cap threads (Hodges

and Williams, 1993), as shown
Figure 1,1. Hole configuration for borehole resin
in Figure 1.2. production method, shown in cross section of the
tree's stem.
Resin production from

borehole tapping is highly variable and species specific, presumably reflecting

genetic differences. Tests with other species used commercially for gum resin

production did not produce appreciable yields, including the sympatric species

longleaf pine (Pinus palustrus Mill) in the southeast US. Borehole resin yields from

slash pine are also sensitive to tapping treatments.

The borehole production system has several important economic, ecological,

and technological advantages compared to conventional gum resin production

systems. First, the labor productivity of borehole tapping is several-fold greater than

conventional methods because of the higher product yield per human intervention.

The average borehole yield per tree is equivalent to that obtained from 4 wounding

treatments with the conventional open-face bark chipping method. Reduced

oxidation and gross contamination of the resin collected in a closed container

results in a higher quality product. Laboratory analysis of borehole-produced resin

showed that it had a higher composition of preferred resin acid species, and a

higher chemical reactivity, which is valuable for manufacturing synthetic resins and


blending (Akzo Coatings, Baxley GA). Capture of volatile terpenes by the closed

container means greater recovery and less emission of volatile attractants for bark

beetles, so pest problems are generally reduced, but not eliminated in borehole

tapping. Because borehole wounds cause relatively little damage to the tree's bark

and cambium tissue, it is expected that there is less disruption of its normal growth

processes, although water transport in the xylem may be impaired. Boreholes are

typically covered by new cambium and bark within about 2 years, and the tree may

be allowed to continue growing without distortion of its form. Since boreholes are

made near ground level, there is little or no damage to the merchantable part of the


The borehole resin production system for slash pine represents a renewable

resource for high quality industrial materials that is sustainable and environmentally

benign. The slash pine resource in 8 southeast US states was estimated at 12.8 x

106 ac, with 11.6 x 109 ft3 growing stock, annual growth of 1.1 x 109 ft3, and

annual removals of 675 x 106 ft3 (Sheffield et al., 1983). Much of the resource is

now intensively managed, and as the pulp and paper industry continues to develop

capacity for using recycled fiber, and demand for virgin wood fiber is reduced, there

will be additional high quality resources available for resin production. There exists a

strong world market for pine chemical products in industrialized countries, with

large import volumes to the United States (Pombo, 1994). Borehole-produced

oleoresin from slash pine is a high quality, value-added non-wood forest product

that is compatible with complete utilization of the tree for wood products and other

forest management objectives. The borehole system can potentially generate

greater economic benefits from pine timber resources, and offer economic

incentives for extended forest rotation periods.



















Ecology and Natural History of the Pine Resin System

Management of resin production systems is fundamentally based upon

appropriate manipulation of the pine tree's chemical defensive behavioral response.

Resins, tannins, phenolics, alkaloids and other secondary compounds evolved in the

higher plants as physico-chemical defense mechanisms against herbivorous

predators, decomposer microorganisms, and mechanical injuries. Many diverse

groups of trees convergently evolved similar structural patterns in their defensive

systems based upon a generalized process of wound compartmentalization to

isolate injured tissues and prevent the spread of decay (Shigo, 1979). In the

coniferous trees (Coniferales), specialized resin ducts arose to produce and store

natural resins throughout the stem, branches, and leaves, as a proactive defensive

strategy. The resin system reached its greatest development in the pine family

(Pinaceae), and its productivity is a key adaptation underlying the success of this

plant group throughout the world under harsh environmental conditions of seasonal

drought, low nutrient availability, and periodic fire. Productivity of the pine's

carbon-based chemical defense system is less limited by site quality than are

nitrogen-based defense systems, enabling the tree's survival in marginal habitats,

and will likely confer a selective advantage to pines under conditions of global

climate change, with elevated CO2 levels providing increased substrate for resin


Pine resin consists of a complex mixture of compounds that impart different

chemical and physical properties and functions to the whole oleoresin (Hodges et

al., 1977). Diterpenes, or resin acids, are double carbon-ring compounds

constituting approximately 70 to 85 percent of the mass of oleoresin, while

monoterpenes are simpler single carbon ring volatile compounds that make up the


essential oil of turpentine (Zinkel, 1981). The terpenes are toxic to insects and

microorganisms, and render woody tissues less digestible to herbivores. The

terpenes exist in phase equilibrium, with the chemical composition of resin acid

species and the overall monoterpene concentration determining whether the whole

oleoresin is a solid or liquid. Solidified and hardened resins impart structural

strength to the wood matrix and act as a mechanical barrier against growth of

lesions. Insect pest pressures on pines in the Southern US are very high, and

oleoresin flow rates and duration are the best predictors of host tree resistance to

beetle attack for the southern pines (Hodges et al., 1977, 1979).

Ecological studies of the pine oleoresin defense system against bark beetle

attack have demonstrated complex dynamic behavior patterns between the tree

host and attacking herbivores (Sharpe et al., 1987, 1985; Blanche et al., 1983;

Hodges et al., 1979). The theme of these models is that different levels of tree

stress factors, such as drought, insect attack, or infection of decay-causing

microorganisms, activate varying responses by the host tree. Terpene emissions by

the tree act as attractants to beetles by signaling its vulnerability. Moderate levels

of combined stress stimulate production of terpenes, but excessive stresses may

overwhelm defensive mechanisms and lead to tree death.

Anatomy and Physiology of Oleoresin Production

Preformed oleoresin is distributed throughout the tree and constitutes about

2 to 5 percent of the dry weight of sapwood and 25 to 40 percent of heartwood in

slash pine (Koch, 1972). It is manufactured by the specialized resin canal epithelial

cells, and secreted into the lumen formed by their continuous tubular organization.

These resin ducts are arranged and interconnected as a network that allows


transport of resin both longitudinally and radially in the stem of the tree, as shown

in Figure 1.3.

Ducts range in size from 20 to
Longitudinal ducts
over 200 microns in inside diameter,

and 0.2 to over 1 m length (Koch,

1972). Radial resin ducts averaged 54

microns in diameter, at densities of 50

to 90 cm-2 in tangential sections, with

lower densities in outer sapwood layers M.'':-
Figure 1,3. Illustration of pine oleoresin
(Mergen and Echols, 1955; Hodges et stem
al., 1981). The vertical resin ducts are

larger, and occur at densities of 30 to 50 cm2 (Koch, 1972).

Preformed constitutive oleoresin stored in the duct system is maintained at

hydrostatic pressures as high as 13 atmospheres (Bordeau and Schopmeyer, 1958)

which serves as a potential energy source to drive oleoresin flow for mobilization to

sites of attack or injury. Resin flow in the ducts is a function of temperature and

viscosity, size and length of ducts, and the pressure differential between source

and sink regions (Schopmeyer et al., 1954). Oleoresin viscosity is inversely related

to ambient temperature. Evaporation of monoterpenes upon exposure to the

atmosphere at a wound site brings about a supersaturated state which leads to

crystallization of the resin acids. Crystallization may also be the immediate cause

for occlusion of resin ducts, stopping resin flow to the environment.

Synthesis of oleoresin occurs to fill new resin ducts formed as the tree

grows, and in response to stresses. Resin acids in oleoresin cannot be

remetabolized or "turned over," so their production is an investment by the tree

(Lawrence, 1971). Newly synthesized oleoresin makes-up for the translocated


preformed resin deposited at wound sites, and may also be manufactured

immediately at wound sites. The mechanism responsible for the induced resin

production response is not well understood, but may be mediated by pressure or

osmotic balance between the resin canal epithelium and the extracellular oleoresin

storage compartment, and influenced hormonally by plant regulators such as

ethylene (Wolter and Zinkel, 1984). Synthesis of oleoresin in the tree competes

with growth processes for the common pool of carbohydrate precursors (Lorio and

Sommers, 1986), and the balance between growth and differentiation processes is

a species-specific trait (Lorio, 1986). Because the monoterpenes are energetically

less costly to produce than diterpenes by virtue of their lower molecular weight,

they may be preferentially synthesized under stress conditions (Paine et al., 1987).

Economics of Commercial Resin Production and Utilization

Production and use of resinous exudates from coniferous trees has been an

important economic activity in many parts of the world for millennia (Hillis, 1987,

Gamble, 1921). Early civilizations of the Middle East region first used natural tars

for building water-tight wooden-hulled sailing vessels; this later lead to the

development of naval stores as an industrial commodity for European empires.

Modern uses of conifer resins include adhesives, sealants, inks, coatings, solvents,

cleaners, antiseptics, insecticides, flavors and fragrances (Zinkel and Russel, 1988).

In commercial use, the monoterpenes and diterpenes are normally separated by

steam distillation to produce turpentine and solid rosin, respectively, as the basic

commodities. Utilization of gum resin in industrialized economies has followed a

trend toward greater fractionation and processing for derivative products of higher



Commercial gum resin production began in the Southern United States in the

1600s, and continued to expand until reaching a peak of 4.1 x 105 metric tonnes

(Mg) in 1910, then declined due to rising labor costs and exhaustion of timber

resources (Gamble, 1921), and production is now less than 1000 tonnes.

Offsetting this decline in the US, the industry rapidly developed in many other

tropical and sub-tropical areas having pine forests, with some 26 different species

used commercially (McReynolds et al., 1988). China, Indonesia, Brazil, Argentina,

Mexico, and several smaller African and Central American countries, are now the

principal producing countries for gum resin, with current world production at

approximately 4.5 x 105 Mg annually, having a value of $200 x 10' (Naval Stores

Int. Yearbook, 1992). Imports to the US amount to 18 x 10" Mg, at a total value of

$11.3 x 106, or $630 Mg-1. Gum rosin produced from slash pine in the United

States is a premium product, with a market value 30 to 40 percent greater than

other rosins, and is typically blended with other materials to make value-added

modified resins.

Gum resin products compete directly with other sources of pine chemicals

obtained by solvent extraction of resinous wood, or tall oil recovery in paper mills,

and indirectly with petroleum derivatives (Stauffer, 1988). Increased production of

wood rosin and tall oil rosin in the US has offset the decline in gum rosin, and lead

the US to continue growing as the largest consumer of pine chemicals (Pombo,


Technology Development in Gum Resin Production Systems

All gum resin production systems involve some means of artificially

wounding the pine tree to open the resin canals and allow oleoresin to drain into a

collecting device. Two trends have occurred in the evolution of technology for


producing gum resin: tree conservation for maximization of long-term tree

productivity through reduced physiological damage of wounding treatments, and

increased labor productivity with treatments to prolong gum flow through internal

progressive wounding action. The modern era of gum resin production began in the

mid-1950's with the advent of bark-chipping and chemical treatment methods,

which are now practiced worldwide. This production system entails cutting-away

strips of bark 1 to 5 cm high at regular intervals of 1 week to 1 month during the

warm season, and applying a stimulant chemical solution to the upper ledge of

freshly exposed bark and cambium on the chipped face of the tree. Chemical

treatments have dramatically improved the productivity of gum resin tapping

operations by simultaneously increasing yields and reducing labor requirements.

Repeated wounding treatments are necessary to remove resin-saturated bark and

phloem tissue, but chemical treatment with sulfuric acid (H2SO4) prolongs the

period of resin flow by slowly diffusing to wound fresh tissue (Ostrum et al.,

1958). The bark-chipping method allows sustained production for an extended

period. In the southeast US, trees are tapped up to 8 months for 8 years, with two

faces equal to one-third the tree's circumference in width.

The latest generation of gum resin production technology involves

stimulation of the pine tree's resin biosynthetic process with plant regulators

(Kossuth, 1984). Applications of 2-chloroethyl-phosphonic acid (CEPA) stimulate

resin synthesis through the action of its breakdown product ethylene gas,

increasing yields up to 36 percent (McReynolds and Kossuth, 1984, 1985). The

extent to which new resin synthesis can be induced by artificial treatments strongly

affects the economic productivity of gum resin tapping.

Insect pest pressures from pine bark beetles (Dendroctonus spp, Ips spp.)

are severe for conventional open-face gum resin production in the US. Preventative


spraying with persistent carbamate insecticides is routine, and costs for pest

control represent a substantial share of total production costs (Merkel, 1981).

Most countries where exotic pines have been planted do not have serious insect

problems for gum resin production.

In response to rising labor costs in the US, mechanized systems were

developed for the chipping operation, including a hydraulic reciprocating hack

(Shaw and McReynolds, 1985), a rotary chipping tool powered by a chainsaw

engine (Clements and McReynolds, 1977), and a tractor-mounted chipper for

streaking trees in plantation stands (Sanders, 1974). However, none of this

equipment was adopted by the industry because of poor reliability or performance

compared to the traditional hand tools. Light weight hand chipping tools enable

proficient workers to chip and treat 400 to 800 trees per day (Clements, 1973).

Improvement of gum resin collection systems in the US has focused on

developing durable containers with chemically inert materials (e.g. HDPE plastic,

aluminum) to avoid contaminating the product. High product losses may occur from

overflow of open collection containers (Hodges and Shoup, 1989). Disposable

paper bags were explored as a convenient, large capacity, efficiently handled

container (Chappel and Harrington, 1971), but the extreme fluidity of slash pine

resin resulted in a large amount of leakage and product loss. In Brazil, Argentina,

and Venezuela, plastic bags are successfully used for resin collection, in both

reusable and non-reusable systems.

Productivity and Behavior of Oleoresin Production Systems

Extensive knowledge about conventional gum resin production systems

offers the best insight into the key factors affecting productivity and behavior of

the borehole resin production system. Pine species tapped for gum naval stores


differ substantially in their productivity under typical commercial tapping, from 1 to

5 kg per tree annually with a regime of multiple treatments (Greenhalg, 1982).

Resin yielding ability is a highly heritable trait. Oleoresin exudation pressure and

terpene composition are heritable traits strongly correlated with oleoresin yielding

ability (Bordeau and Schopmeyer,1958; Barrett and Bengston, 1964; Squillace,

1971). A genetic improvement program for slash pine resulted in a 65 percent gain

in resin yields (McReynolds and Gansel, 1985). The two principal southern US pine

species used for gum production, longleaf and slash pine (P. palustrus, P. el/iottil),

have remarkable differences in resin qualities, and divergent sensitivities to yield

enhancing treatments (Kossuth, 1984).

Slash pine is a favored species for its high resin production, and has been

widely planted and used for this purpose in Brazil, Argentina, New Zealand, South

Africa, and Zimbabwe. Yields for slash pine in its native range in the southeast

United States averaged about 7 kg annually from a typical 10 inch DBH tree, with a

regime of 8 monthly streaks, using the best available CEPA paste treatment

formulation (McReynolds and Kossuth, 1984). Physiographic conditions interact

with genetic resin yield factors, and annual resin yields from slash pine planted in

tropical regions have been reported equal or lower than in the US (Young, 1981;

Taylor, 1985). Labor productivity of typical commercial gum resin production

operations in the southeast US was estimated at 43 kg per man-hour, including

labor for both the chipping and harvesting operations, using a discrete-event

simulation approach (Hodges and Shoup, 1989).

Descriptive studies of commercial oleoresin yields have confirmed the dual

nature of resin production from two sources: preformed oleoresin stored in the resin

duct system, and newly synthesized oleoresin. Initial yields of oleoresin depend

mainly upon the supply of preformed oleoresin, and tree stem diameter is the most


reliable predictor of first-year yields. Yields are also related to the area of tissue

wounded, with larger stem surface area wounds resulting in higher yields, but

declining amounts per unit area (Snow, 1954). Resin flow was reported greatest

from the region of wood near the edges of the naval stores bark-chipped face

(Larson, 1955).

Resin production over an extended period of several years is influenced by

the supply of newly synthesized oleoresin, with yields during a second or third year

often greater than for the first year, due to the formation of traumatic resin ducts

above the worked face (Gerry, 1935). As indicators of photosynthetic capacity,

tree canopy and wood volume growth rate are reliable predictors of long-term yields

(Snow, 1954; Schopmeyer and Larson, 1954). The stimulant chemical CEPA

appears to exert its effects over an extended period by activating new resin

synthesis, with the greatest enhancement of production during the latter part of the

season (McReynolds and Kossuth, 1984, 1985). CEPA appears to preferentially

stimulate production of monoterpenes (Kossuth and McReynolds, 1987).

Investigations of resin flow over time from conventional gum resin

production have shown that flow rates are highest immediately after chipping/acid

treatment, then decline exponentially and reach a negligible level within 4 weeks

(McReynolds and Kossuth, 1984; Harper and Wyman, 1936). Flow rates are related

to air temperature, with substantial flow occurring only during periods when

average daily temperature exceeds 20 deg. C, and maximum flow occurring during

the months of July and August in the southeastern US (Harper and Wyman, 1936;

Clements, 1961). Flow rates respond to seasonal temperature variations most

strongly on the first day following chipping/acid treatment, and become less

sensitive over time.


Empirical investigations of the effect of conventional gum resin tapping on

growth rates in slash pine have shown highly variable results, with measured

reductions in growth ranging from zero to 26 percent of normal growth rates,

depending upon the type and intensity of tapping treatments (Schopmeyer, 1955),

and genetic strain (Franklin and Gansel, 1975). These studies showed that the

impact of resin tapping varies over time, causing greater growth reduction later in

the season and in subsequent years of production. This finding is consistent with a

model of resin production as a dual process: an initial period of draining preformed

oleoresin from the resin ducts at high potential flow, then a period of new resin

production from carbohydrate reserves. According to the theory of carbohydrate

partitioning, it is expected that the latter phase of this process would result in

reduced tree growth. To the degree that any resin tapping process activates the

tree's defensive response, it could cause slowed growth. On the other hand, if the

tapping process merely drains preformed oleoresin from physiologically inert stores,

there may be little effect on tree growth.

Related Tree Extractive Production Systems

Insight into the nature of the borehole resin-tapping system is also available

from a similarly internalized resin production system concept, developed as a one-

time treatment to stimulate resin deposition in the stemwood of pines for recovery

during processing at pulp mills (Stubbs, Roberts and Outcalt, 1984). This

lightwoodd" production system involved treating the tree with Paraquatt" or related

herbicides by means of bark streak, frill, or borehole wounds, to cause a generalized

wound response, and necrosis of the resin duct system over a period of 6 to 18

months. Extensive resin saturation of the xylem up to 5 m above the treatment site

resulted in a 4-fold increase in oleoresin content of the tree stem on a whole tree


basis (Brown and Pienaar, 1983). This production system was not adopted

commercially due to massive insect attacks and high tree mortality as a

consequence of severe tree stress by herbicide injury.

The pattern of resin deposition caused by herbicide injury is relevant to the

borehole tapping system. Notably, resinosis always occurred in a pie-shaped sector

area, following the structure of the ray parenchyma and radial resin canals. The

extent of resinosis was especially variable in height above and below the treatment

site, presumably due to variation in transport of herbicide in the transpiration

stream. Ingenious experiments which isolated the xylem from the phloem

demonstrated that the source of oleoresin for resinosis is within the locally injured

tissue, not translocated from other parts of the tree stem (Wolter and Zinkel,

1984). A preferred method for applying the herbicide to maximize resin production

specified drilling multiple equally-spaced boreholes at tangential and vertical angles,

such that approximately one-half of the tree's radial rays were intersected (Brown

and Enos, 1976). The chemical CEPA also caused resinosis, both alone and

synergistically with Paraquat (Roberts, 1983). CEPA treatments in borehole wounds

to the stump caused resinosis in a region approximately 0.9 m above and 0.3 m

below the treatment site (Kossuth and Koch, 1989).

The Maple sugar industry in the Northern US and Canada is the closest

example of a borehole production system for collection of exudates from living trees

(NEFES, 1981). Although the maple sap system is completely different

physiologically from the pine resin system, there are remarkable similarities in the

defensive behavior of trees in response to tapping treatments, which gives insight

to the dynamics of tree borehole exudation. The pattern and intensity of multiple

tapholes drilled in the maple tree affects the local supply of sap and the pressure

potential of exudation. If the tree is "overtapped" with too many tapholes, yields


decline and extensive deposition of defensive chemicals occurs in the heartwood

zone (Walters and Shigo, 1978). The technological developments of tubing

collection systems and vacuum pumping (at 0.3 atm) resulted in a nearly four-fold

increase in sap yields, demonstrating a controlling effect of pressure potentials

(Walters, 1978).


The concept and technical feasibility of the new borehole resin tapping

technology was demonstrated in field tests which showed that economically

attractive yields were obtainable from Slash pine, but irregular results made unclear

the potential range for its application. So, a first objective of this research was to

broadly characterize the nature of borehole resin production with respect to

different species, site conditions, and weather patterns. Development of a

conceptual working model of the borehole resin production system was a research

objective to support continued technology innovation and management, through an

understanding of fundamental controlling factors.

Maximization of resin yields is a primary goal for management of all gum

resin production systems, in order to achieve high productivity and utilization of

labor and forest resources. High variability in borehole resin yields suggested that

there was a substantial potential for yield improvement through appropriate

resource selection and tapping treatment design. Therefore, an objective for this

work was to determine tapping treatments, resource factors, and environmental

conditions which maximized resin yields.

The high level of variability in borehole resin yields also represented a

problem for system management in terms of process reliability and the ability to

detect process shifts in response to changes in treatments or environmental

conditions. From the standpoint of industrial process engineering, it was concluded


that the borehole resin production process was "out of control". Therefore, an

objective for this work was to establish a greater degree of operational control over

the borehole tapping process. Increasing the reliability of predicted yields required

developing an accurate statistically predictive model of resin production, with the

goal of minimizing variability about the expected value as well as maximizing yields.

The borehole production system is sensitive to tapping treatments,

and determination of the best combination of these treatment factors for

maximizing yields is an essential task for management of the system. Borehole

depth, diameter, and orientation, chemical treatment levels, and number and

spacing among multiple boreholes are possible parameters for manipulation. An

objective of this research was to experimentally measure the effects of various

treatment levels and treatment combinations on resin yields.

Analysis of borehole tapping productivity required development of

standardized equivalent measures of yields and tapping treatment intensities. Of

particular interest is to describe yields in terms of the areal extent of tapping

treatments, in order to evaluate economic tradeoffs for treatment strategies. An

area-based model of resin production in the tree's stem was developed to express

yields on a unit area basis, and to represent tapping intensity as a function of the

proportion of the tree's cross sectional area tapped.

Selection of suitable forest tracts is a key area for management of the

borehole resin production system. Experience with the conventional gum resin

production system and early borehole tapping studies showed that tree size was an

important factor affecting resin yields, and is probably the best single indicator of

resource quality for borehole tapping. Although large diameter timber is more

productive for borehole resin tapping, it has a higher economic opportunity cost

(rental price) due to its greater value for wood products utilization, and is


associated with a greater risk of damage. The economic rental price of timber for

resin production is expected to shadow general timber market prices, and the

supply of high quality softwood timber is expected to become increasingly scarce

over the long run (USFS, 1982; Ince, 1994). Assessment of borehole resin

productivity as a function of tree size was therefore an objective of this research.

Determination of the minimum acceptable tree size has consequences for the

overall supply of timber available for tapping.

It is likely that the tapping treatment conditions which maximize borehole

resin yields will interact with different levels of resource quality, such that the best

treatment for a small trees will differ from the best treatment for large trees.

However, adjustment of treatment procedures on a tree-by-tree or tract-by-tract

basis is associated with a higher management cost than for a uniform treatment

regime. Determination of the single best treatment for maximizing yields for all tree

sizes was a goal for this research, along with assessment of the value of a

condition-dependent flexible borehole treatment strategy.

In temperate zones, resin production follows a seasonal cycle, with highest

flow rates occurring during the warmest period. The seasonality of resin production

is important for management to organize and schedule tapping and collection

operations to achieve a high level of labor and capital utilization. To the extent that

production departs from an ideal of a year-round steady state, there exists some

inefficiency in resource utilization. An objective for research was to measure the

seasonality of borehole resin production.

The economic cost of borehole tapping for its use of the forest resource is

partly gauged by any effects it may have on tree growth or mortality. Logically,

borehole tapping or any kind of exudate extraction is expected to cause some

reduction in growth or vigor of the tree, insofar as this represents competition for


its carbohydrate reserves. However, the loss might be so small as to be

inconsequential, or undetectable, since there is wide variation in the genetic

predisposition to allocate nutrients between growth and defensive functions (Lorio,

1986). An objective for this project was to measure the effect of borehole tapping

on tree growth rates.

The resource cost of borehole tapping is also partly determined by the length

of time used, and the production period in relation to the overall forest rotation

length. The rate of resin flow over time represents the marginal physical

productivity and the incremental product recovery. Following from standard

economic theory, the optimal duration for resin production occurs at the point when

marginal costs equal marginal benefits. To evaluate alternative production

schedules and to validate the systems model of borehole resin production, an

objective for this research was to experimentally measure resin flow rates over


Borehole tapping causes physiological stress in the pine tree, as does any

form of injury. An appropriate level of stress is necessary to activate the tree's

defense response in order to obtain good resin yields, but excessive stress may

result in undesirable effects, such as defoliation or insect attack, and ultimately

reduce resin yields. A task for management of the borehole production system is to

optimize tree stress levels through control of treatment intensities in relation to

resource qualities and strategic management objectives.

Two alternative scenarios are envisioned for operation of a commercial

borehole production system. One scenario involves intensively tapping trees for a

relatively brief period immediately before they are harvested, with the objective of

obtaining the highest possible yields in the shortest possible time. Since the trees

are to be cut soon anyway, there is little concern for possible negative impacts on


tree health arising from chemical injury or insect attack, but there is a highly time-

dependent opportunity cost. A second approach is to conservatively tap trees for

an extended period, perhaps several years, with multiple treatments, to maximize

long-term yields and forest resource utilization, and simultaneously minimize

potential side effects. A specific objective for research was to measure production

during a second consecutive year of borehole tapping.

High labor productivity and utilization is a key advantage of the borehole

resin production system over conventional systems, and is essential to its

commercial success and proliferation. A research objective was to evaluate new

equipment for mechanized borehole tapping operations, including a semi-automated

hydraulic-powered drilling machine and a specially manufactured spout-bag resin

collection apparatus. Specific objectives were to evaluate clustered borehole

configurations associated with mechanized systems for their effect on yields, and

to assess the appropriateness of new systems by comparison of overall labor

productivity of mechanized vs. non-mechanized systems.


The purpose of this conceptual model is to provide a framework for

understanding the fundamental factors affecting productivity of the pine oleoresin

borehole tapping system, and for predicting yields in response to tapping

treatments, over time and on a seasonal basis, for a range of tree sizes. The

borehole production system is conceptualized as a closed-channel hydraulic system

with storage of preformed oleoresin in capillary vessels, mass flow to the container

through openings in the resin canal network, and inputs of newly synthesized

materials from secretary cells, as depicted in Figure 3.1.

Figure 3,1. Schematic representation of borehole resin production system.


The borehole tapping system may be generally described in terms of 3 basic

features: capacity, conductance, and pressure potential. The capacitance of resin

available to borehole tapping is a function of tree stem volume, preformed resin

density, and resin secretion rates. Density of preformed oleoresin stored within the

tree's resin duct network is determined by the diameter, length, and density of

ducts. Flow conductance from the extracellular resin store is affected by the extent

of borehole wounding treatments and chemical composition and viscosity of the

oleoresin itself. Pressure potentials driving resin flow arise from the mechanical

elastic properties of the resin canal epithelium, xylem tissue turgor, and the vapor

pressure of the collection container. An osmotic chemical potential exists between

the resin secretary cells and the extracellular resin store, and is affected by CEPA

chemical stimulation treatments.

Borehole wounds in the pine tree sever both radial and longitudinal resin

ducts which form a network of drainage pathways, with directly and indirectly

tapped ducts, as shown in Figure 3.2. Resin ducts directly intersected by boreholes

have greater flow magnitude than those indirectly tapped by virtue of their shorter

path length. Flow conductance of the resin ducts is a function of number of ducts

sectioned, duct size (diameter and length), pattern of radial and longitudinal duct

interconnections, and oleoresin physico-chemical properties, such as monoterpene

content, viscosity, and crystallization rate.

Fundamental Laws Governing Resin System Behavior

Oleoresin flow was described by Poiseuille's law as expressed in equation 1,

where the first term represents the pressure gradient driving flow along the duct,

and the second term represents frictional resistance to flow within ducts.

Radial View

Longitudinal resin ducts

S_ Bark

Radial resin duct

-- -- Boreho le

Figure 3,2. Flow pathways to a borehole wound in the resin duct network.

AP r4
A/ 819
where y is flow rate,
AP is pressure difference, (1)
Al is vessel length,
r is vessel radius,
n is viscosity.

This model explained 75 percent of the variation in oleoresin flow rates for

conventionally tapped slash pines (Schopmeyer et al., 1954). The opening diameter

of resin ducts strongly affects the potential velocity of viscous flow, with the result

that a few large-diameter ducts may dominate flow in a network of parallel

pathways (Siau, 1971; Erikson, 1938). The velocity profile of a viscous fluid

follows a parabaloid function of distance from the capillary wall, giving rise to the

fourth power term in equation 1.

Pressure potential (P in eq. 1) is the driving force behind resin flow, and is a

function of the difference in hydrostatic pressure between the resin duct system


and the external environment of the borehole wound and collection device. The

potential energy stored in the pressurized fluid oleoresin is controlled by the

mechanical elasticity of the resin ducts and the active chemical transport of

secretion by the resin duct epithelial cells. The hypothesized general relationship

governing oleoresin potential in the storage compartment is indicated in Figure 3.3,

where pressure rises linearly with increased volume above a certain "rest volume"

(VR), which corresponds to the capillary pressure (PA) in its discharged state.

The pressure required to

express a viscous fluid from a rere

capillary is an inverse function

of capillary diameter (Siau,

1971). The relationship is

described by equation 2, where p

the left hand side is the pressure
potential difference (psi) R
Vo I ume
between the capillary and the
Figure 3,3--Relationship between oleoresin
environment, R is the vessel pressure and volume in the oleoresin duct store.

radius (micrometers), and A is a constant representing the specific capillary

adhesion of the material (A =90 for Hg).

The consequence of this relationship is that only a portion of resin ducts contribute

to flow at a given pressure potential. Changes in the pressure potential correspond

to a change in the minimum diameter of ducts which can be expressed, as

described by the curve in Figure 3.4.

P -Po -A

Pressure potential

differences may be
(n 1,2 -
influenced by borehole C
LJ 1 0 -

tapping techniques.
Tightly sealed borehole o -

collection containers 0 -
essentially act as closed- 0 2

Capillary Radius Cmicrons)
gas pressure in the
Figure 3,4. Pressure required to express a viscous fluid
headspace rising as a (Hg) from a capillary as a function of capillary diameter.

function of resin volume, according to the relationship depicted in Figure 3.5, and

described in equation 3, where the change in pressure (in atmospheres) represents

the gas compression ratio, C is the capacity of the container (2000 ml), Y is resin

yield (gm), and D is resin density (1.065 gm/ml).

,c Y (3)

This functional relationship is based upon Boyle's law for an ideal gas, where the

product of pressure and volume is a constant. An increase in the container pressure

corresponds to a decrease in the net system pressure potential. It is expected that

the ultimate yield under these conditions is indicative of the inherent pressure

potential of the tree.

The pressure potential of the oleoresin store may also vary due to changes in

the turgor pressure of ambient woody tissue surrounding the resin ducts (Lorio and

Hodges, 1968; Vite, 1961). Water is transported in the xylem under negative

pressures exerted by evapotranspiration (ET) in the canopy, with diurnal and

seasonal variation in
U) 20
oleoresin system )
pressures accompanying E

changes in xylem water
) 10 -
potentials (Zimmerman, L
1983). Interruption of the a
U) 5 -

transpiration stream by
0 I I I I I 1
borehole treatments is a 200 400oo 500 00o 1000 2oo 1400 oo 100 200ooo
Resin Yield (gm)
likely to cause cavitation
Figure 3,5. Gas pressure in sealed 2-liter borehole
in tissues above holes, containers as a function of resin yield.

but could result in increased pressures below holes due to separation from the

negative potential source.

Xylem water potentials are normally lower in the interior portions of the

stem due to general senescence processes, reflected by deposition of extractives

and heartwood formation (Hillis, 1987). It is hypothesized that reduced oleoresin

exudation pressure potentials will result in lower resin yields from boreholes which

penetrate this region, and the incipient heartwood tissue may act as a sink for

deposition of oleoresin (Figure 3.1).

A hypothesized model of resin flow over time is shown in Equation 4, where

parameter B, represents capacitance and potential factors determining the

cumulative final yield of resin, and parameter B2, the time constant, represents resin

flow conductance.

yT =B,(1 -ea'4) (4)

This model was fitted to data for resin yields over time. The negative exponential

form of this flow rate function implies a fixed capacity flow source system (France


and Thornley, 1984), and is consistent with resin flow rates observed in

conventional gum resin tapping (Harper and Wyman, 1934; McReynolds and

Kossuth, 1984, 1985). It is also hypothesized that the sensitivity of the borehole

resin system to environmental perturbations follows this same functional

relationship, as was shown for the effect of weather conditions on conventional

open-face resin production (Harper and Wyman, 1936).

A Basal Area Representation of Oleoresin Storage and Flow

As a consequence of the arrangement of radial resin ducts, the effective

region of tissue tapped by borehole wounds is bounded by a pie-shaped sector of

the tree stem subtended by the horizontal extent of the hole, as shown in Figure


This sector is indirectly

drained above and below

the hole due to the dense

interconnection of radial

and longitudinal resin


An area-based

representation of tree
Figure 3,6. Resin flow in the borehole production system
resin store capacity was from radial sector area.

chosen because of its generality for tree growth processes, and the availability of

forest yield models developed in terms of tree basal area per unit land area (e.g.

Bailey et al., 1982, Pienaar et al., 1990). A volume-based representation was not

possible because the length of longitudinal resin ducts is not known precisely.


The stem cross-sectional area was divided into three compartments as

depicted schematically in Figure 3.7 for three types of borehole configurations.

Offset Hole

Key to CoResin system compartment Areas for borehole tapping.
Hoe area of the boreholee Areasitself is the "hole" compartment. An "outer" compartment

area of the stem is a sector extending from the radius projected from the tip of the
Inner Areas between radial lines projected to extreme corners of the hole

Non-Tapped Areastimation of their relative contribution to the total flow. For all three

Angled Hole AWH, 2/95

Figure 3,7. Resin system compartment areas for borehole tapping.

The area of the borehole itself is the "hole" compartment. An "outer" compartment

area of the stem is a sector extending from the radius projected from the tip of the

hole, to the lateral face of the hole, while an "inner" compartment occupies the

residual sector area between radial lines projected to extreme corners of the hole

profile. Comparison of yields per unit area of the respective compartments will

allow a gross estimation of their relative contribution to the total flow. For all three

hole configurations, the sector angle subtended is sensitive to the depth of the

hole, especially as holes approach the center of the stem.

Resin flows centripetally from the outer compartment, and centrifugally from

the inner compartment. This pattern differs fundamentally from that occurring in

nature and in the conventional open-face production system where resin flows only


from the radial ducts in a centrifugal direction. The fact that resin flow in the

centripetal direction occurs along a decreasing water potential gradient in the tree's

stem is probably a key factor for productivity of the borehole tapping system.

Management Related System Factors and Experimental Treatments

To validate, calibrate, and apply the conceptual model of the borehole

oleoresin production system to the operating management of a borehole tapping

enterprise, a series of experiments were conducted that manipulated the

fundamental system factors. Experimental factors available to test the conceptual

model of the borehole resin production system are summarized in Table 3.1.

Hole dimensions and orientations are matters for both system design and

day-to-day management of borehole tapping, and generally, these treatment factors

affect both capacitance and pressure potential system factors, but in opposing

directions. The cross sectional area of longitudinal resin ducts directly tapped is

proportional to the depth, diameter, and number of boreholes, while orientation of

the hole axis, both horizontally and vertically, affects the number of radial ducts

sectioned. Horizontal and vertical separation of adjacent holes affects the number

of second-order pathways tapped. Spacing among holes affects the local tissue

pressure potentials, but effects may not be directly additive due to overlapping

zones of influence. Following from economic principles, it is predicted that there

exists an optimum level of borehole extent where the rate of increased yield due to

greater capacity is equal to the rate of decrease due to reduced pressure potential.


Table 3.1. Summary of resin system management domains, model factors and
experimental variables.

Management Domain Experimental Variables System Model Factors

Hole extent and Hole diameter Capacitance, Potential
placement treatment Hole depth
factors Hole depth
Hole vertical orientation
Hole horizontal orientation
Number of holes per tree
Hole vertical separation
Hole horizontal separation
Chemical/biological CEPA level Potential, capacitance
treatment factors
Sulfuric acid (H2SO4) level Conductance,
Fungal culture extract Potential, capacitance
Borehole technology Borehole machining quality Conductance
Sprayer type Capacitance
Collection container Potential
Resource selection Species, variety Conductance,
factors Capacitance, Potential
Tree size Capacitance
Physiographic region Capacitance, potential
Site quality Capacitance, potential
Production Seasonality of treatment Conductance, Potential
scheduling ___

Chemical and biological treatments of borehole wounds affect capacity,

conductance, and pressure potential factors. Chemical treatment with CEPA

stimulates resin synthesis, which simultaneously increases production capacity and

maintains pressure potentials in the resin duct system. Sulfuric acid treatment acts

to increase conductance by destroying cells which surround the openings of

severed resin ducts, and delay the onset of duct occlusion (Ostrum et al., 1958).


Biological treatments with extracts of fungal cultures have been shown to increase

the flow of oleoresin from wounds within 2 days of wounding (Popp et al., 1991),

and decrease sapwood conductance after colonized by the fungi (Parmeter et al.,

1992), so it could conceivably enhance or reduce borehole resin yields.

The borehole treatments can be understood in terms of the intensity of their

effects on the fundamental system factors. In general, larger hole extent and higher

chemical treatment concentrations or molar volumes are expected to inflict higher

intensity effects on the resin system.

Other factors pertinent to management of the borehole resin production

system which are reflected in the system model are technological, resource quality,

and seasonal factors. The borehole container type affects pressure potentials, and

is a discriminating factor between capacitance and potential. Tree size determines

the overall capacity of the system. Site quality may have complex effects on

system capacitance and potential due to alterations in the balance between growth

and differentiation. Time of year for borehole treatment is expected to similarly

affect system behavior through capacitance and potential, with seasonal variation in

oleoresin exudation pressure, and additionally through the effect of temperature on

resin conductance.


Research Sites and Plots

Borehole-tapping studies with Slash pine were conducted between 1991 and

1994 at eight sites in Florida and Georgia (USA), which are summarized in Table

4.1. Resin yields were measured for 668 trees and 1575 boreholes, including 1337

individual borehole measurements in 528 trees. Trees were 25 to 40 years old, with

diameters at breast height (dbh) ranging from 18 to 41 cm (7 to 16 inches). Site

quality indices for slash pine ranged from 24.4 to 28.0 m height at 25 yrs.

Table 4.1. Sites and plots for borehole tapping experiments, slash pine, 1991-94.

Site Location

Site Index Average Date Began Period Number Number
(meters Tree DBH (Days) Trees Holes

Gainesville, FL

Waldo, FL
Hosford, FL

Homerville, GA
McRae, GA

Soperton, GA
Eastman, GA
Waycross, GA

ht. at 25






na 1-Jul-93


140 240

668 1,575



Resin production was measured for periods of 99 to 199 days between April and

December. A small number of Longleaf pines (Pinus palustrus) were incidentally

tested for borehole resin production during these experiments, and small numbers

of tropical pines (P. caribean, P. oocarpa) were tested in Venezuela. A factorial

experiment with Maritime pine (Pinus pinaster) was conducted in the Landes region

of southwestern France during September 1994, in a 50 year-old stand with 110

trees and 297 total boreholes.

Borehole Treatment Procedures

Borehole tapping experiments followed three operational steps: boring holes

in the tree at the prescribed position, depth, and orientation; applying a chemical

spray treatment; installing the resin collection apparatus. Each of these steps

involved technology innovations, for development and testing of a mechanized

tapping system, as described in the final section.

Hole boring was done with a double-spur, double twist self-feeding drill bit

2.54 cm in diameter (1.0 inch) at approximately 1000 rpm. This type of drill bit has

a very clean cutting action to avoid tearing wood fibers, and a self-feeding screw

point that controls the drill feed rate. The drill was powered by a 2.2 kw chainsaw

engine and drilling attachment (Atom Industries, Sydney, Australia). Holes were

drilled to a depth of 5.1 to 17.8 cm, measured from the bark-xylem interface.

Chemical spray treatment was done immediately after boring holes to get

good spray contact and uptake before the quickly-exuding resin covered and sealed

the wood surface. Spraying was done with either a naval stores spray bottle, a

11.4 liter pressurized sprayer, or hand-held pump sprayer. The naval stores spray

bottle (Evans) is a finely atomizing aspirated sprayer, which is used throughout the

world in gum resin operations. The pressurized sprayer (2.8 kg/cm2) was a garden-


type spray tank which produced a similarly fine spray particle size. The common

household-type hand pump sprayer produced a somewhat coarser cone-shaped

spray pattern, but delivered a constant dose by virtue of its fixed volume

displacement. Chemical solutions were mixed in volumetric concentrations of 0

percent to 15 percent (ai) of 2-chloroethyl-phosphonic acid (CEPA, Rhone-Poulenc

Co.) and 0 to 25 percent sulfuric acid (H2SO4). Chemical volumes of 1 to 2 ml

were applied to each hole, resulting in dosages of 0 to .28 ml a.i. of CEPA.

Sterilized extracts of the Blue Stain fungus (Ophiostoma spp) were applied

as an additional biological treatment in experiments at Gainesville FL in 1994. The

extract was prepared from a laboratory strain of Ophiostoma cultured on an agar

medium, by homogenizing, then autoclaving to kill the microorganisms, and filtering

through cheesecloth to remove large particles of mycelia. The sterilized extract was

mixed with a stock solution of CEPA and H2SO4 to give a concentration of 2.1 x

10' spores ml1, in order to apply a target population of spores 1.05 x 106 cm-2 hole

cross sectional area, following from Popp et al. (1991).

Containers used for resin collection from boreholes were either 2-liter PET

bottles or a spout-bag apparatus. For the first three-year's experiments (1991-93),

recycled 2-liter PET beverage bottles were attached for resin collection by screwing

into the borehole with the bottle's existing cap threads and left in place for the

duration of the season. A spout-bag collection device was a key technological

innovation introduced in the last year of the project (1994), which enabled

measurement of resin flow rates over time. Two types of spouts used were a

general purpose hose adapter (PVC 3/4" NPT), and a specially manufactured

injection-molded HDPE device (patent-pending, Navstoc, Inc., Boca Raton, FL). Both

types of spouts were installed by gently hammering with a small mallet or pushing

with the palm of the hand to achieve a compression fitting in the hole. Individual

plastic bags made of HDPE or LDPE were attached to spouts on each borehole, and

were repeatedly replaced to collect resin flow for periods of 1 to 2 months. The

spout-bag and PET bottle collection devices are shown in Figures 4.1 and 4.2.

The different treatments and their levels used in all experiments are

summarized in Table 4.2. A total of 11 different experimental variables were

manipulated with 2 to 7 discrete levels of each treatment variable, however, only 2

or 3 levels of treatment variables were manipulated simultaneously in a given


Table 4.2. Treatment variables and levels used for borehole tapping experiments,
Variable 3 Treatment Levels

Hole depth 8.9, 10.2, 11.4, 14.0, 15.2, 17.8 cm

Hole vertical orientation 0 or 45 deg. from transverse horizontal
Hole horizontal orientation 0 to 25, 30 or 45 deg. from radial plane

Clustered hole horizontal 4.8, 7.6, 9.7, 10.2, 15.2 cm
Clustered hole vertical separation 0, 4.78 cm
Number of holes per tree 1, 2, 3, 4, or 5 holes
CEPA dose (ml/hole) 0.0, 0.02, 0.04, 0.08, 0.12, 0.15, 0.18,
0.28 ml/hole
Sulfuric acid (H2SO4) dose 0.0, 0.2, 0.3 ml/hole
Fungal culture extract of yes, no

Collection container 2 liter PET bottle,
PE spout/bag apparatus
Month of treatment/installation April, May, June, July, August, September








c) 0






















Yield Measurements and Tree Observations

Net resin yields were measured by weighing resin containers for each

borehole with a spring scale to the nearest 5 g or 25 g. Cumulative seasonal yields

were taken for all trees at 99 to 199 days since drilling. Intermediate yields were

measured for 79 trees at Gainesville FL in 1994, at 7, 25, 50 and 84 to 112 days

following borehole treatment.

Tapped trees were observed for signs of physiological stress, including

discoloration or loss of leaves, attacks by Black Turpentine beetles (Dendroctonus

terebrans), presence of other wood and bark boring beetles (Ips spp.), and

mortality. Loss and discoloration (browning) of the leaves, which occurred in some

trees as a result of CEPA treatment, was estimated as a percentage of the canopy

affected. Attacks by Black Turpentine Beetles (BTB) were noted on a weekly basis

by counting the number of fresh and old pitch tubes present on the lower tree bole.

During periods of massive BTB attacks, trees were sprayed with Lindane. A

composite index of tree stress was developed by combining the measures for

individual stressors of canopy defoliation, and incidence of beetle attacks.

Weather data for the period of 1994 experiments in Gainesville FL were

obtained from the nearby National Weather Service station, by retrieval from the

AWARDS database maintained at the University of Florida. Daily records were

compiled for photosynthetically active radiation (PAR), average, maximum and

minimum temperatures, rainfall, and humidity. Effects of daily and cumulative

weather fluxes on resin flow rates in the four seasonal plots were tested by

statistical analysis.

Design of Borehole Tapping Experiments

Borehole tapping experiments included simple yield tests with no treatment

variation, controlled studies of a single treatment variable, and intensive studies in

which multiple treatment factors were systematically varied. The simple field tests

at the Soperton (1991), McRae (1991), and Waycross (1993) sites involved 2 to 5

uniformly treated boreholes installed in each tree at evenly spaced circumferential

positions. Controlled experiments with paired treatments in each tree were done at

McRae site (1994) to measure the effect of collection container types (2-liter PET

bottles vs. spout-bags), and at the Hosford, McRae and Eastman sites (1993) to

test large vs. regular diameter boreholes. Intensive studies with factorial

experimental designs were conducted at Gainesville FL in 1994, at McRae GA and

Waldo FL in 1992, and at Hosford FL in 1992-93.

Investigations at Austin Cary Forest near Gainesville (1994) were designed

as a replicated series of plots with fractional factorial experimental arrays and

within-subject experimental controls. Treatment levels were blocked to obtain the

greatest possible number of within-subject (tree) experimental contrasts, and were

roughly balanced in numbers. These procedures were taken in order to increase

statistical power to detect relatively small treatment effects against the large

background variability between trees. A total of 318 boreholes were made in 99

trees, with 3 or 4 boreholes each. Four separate experimental plots were

established in April, June, August, and September, with 15 to 44 trees each, to

measure seasonal effects on borehole tapping yields (Table 4.1). In the April, June,

and September plots, the fractional factorial experimental design tested the effect

of hole number, depth, vertical orientation, horizontal spacing, and CEPA chemical

spray treatments. Groups of 2 or 3 clustered holes were installed in various


combinations of spacing and depth as shown in Figure 4.3. Trees in these plots also

included a within-subject control in the form of a single borehole receiving uniform

treatment on the opposite side of the tree. Hole number, depth, orientation and

spacing treatments were administered at two levels representing "high" and "low"

values, while CEPA spray treatments were made at three levels representing "high",

"low" and "medium" values. These five factors were arrayed by cyclical

permutation in a total of 36 different combinations, as shown in Table 4.3.

Experimental treatments at Gainesville (1994) were also stratified for

balanced random assignment within three tree size classes as a control for resource

quality (tree size) effects. This form of experimental design was used to develop

process settings that maintain robust control of yield responses in the face of

environmental variation.

2 holes clustered
Narrow Spacing Wide Spacing
Deep Sha I Iow Sha I Iow Deep

3 holes clustered

Al I holes 1" diameter 2

Figure 4,3. Hole treatment patterns for clustered experimental holes at narrow and
wide spacings, and deep (17.8 cm) or shallow (8.9 cm) depths, with a single
control hole (8.9 cm deep) on opposite side.

Table 4.3. Design matrix for fractional factorial borehole tapping experiment,
Gainesville FL, 1994, June plot. Numbers indicate treatment levels.

Tree Tree

Number Horizontal
of Holes Separation
between Holes

2 1
3 1
2 2
3 2
2 1

Angle of

CEPA Depth of
level Hole

Compartment Model Area Calculations

The cross-sectional areas of the tree stem affected by borehole-tapping

treatments were calculated for the three-compartment model illustrated in Figure

3.7, using the parameters shown in Figure 4.4.

Offset Hole -A---
4 Tree circLumference
Inside bark
Outer Area

SAWH, 12/94
Figure 4,4. Area calculations for compartment model.

Formulae for calculating areas (cm2) were developed for the three basic hole types--

radial, angled, and offset--based upon a Cartesian coordinate system for the corner

points of each hole, with the center of the tree as the origin (0) and a radial axis

through or parallel to the hole (line ab). The tree radius inside bark at a height of 6

inches (R) was estimated from DBH measurements using a formula from Bailey

(1994) which described stem taper and bark thickness as a function of height

above ground. Sector areas subtended by rays projected to the extreme corner

points of holes were calculated from trigonometric formulae (areas 0-3-5-0, 0-8-

11-0, 0-16-14-0), using the interior angle of the sector (B). The cross sectional

area of the hole itself was approximated as a polygon (areas 1-2-3-4, 6-7-9-10-6,


12-13-15-14-12). The inner compartment areas were calculated either as a triangle

(areas 0-6-7-0, 0-12-14-0) or a concave polygon (area 0-1-2-3-0). The outer

compartments (areas 1-4-5-1, 13-15-16-13, 6-8-9-6 and 7-10-11-7) were derived

as the residual of the total sector area. Compartment areas for each hole were

divided into the hole yield to derive intensive measures of yields per unit area.

Areas and yields were also summed for each tree to analyze area-specific yields on

a whole tree basis. In the case of downward-oriented holes, the horizontal profile

projected by the hole was used to calculate its compartment areas, and for cases in

which the hole reached the center of the tree stem, sector angles and areas were

not calculated.

Increment Core Analyses for Borehole-Tapped Trees

To test the effect of borehole resin production on tree growth, increment

cores were taken and measured in the field for groups of 41 tapped trees and 25

neighboring untapped trees on two different sites, at McRae GA, in February, 1994.

The tapped trees had been tapped for 120 days from June to October in 1992.

Tapped and untapped trees selected for core sampling were matched with respect

to tree size on both sites (avg. DBH 24.6 vs. 25.4 cm). Increment cores were taken

at breast height. The width of rings on each core was measured (to nearest mm) for

the last 2 years and 5 years, providing a measure of radial growth during the 3 year

period before tapping and the 1.8 year period since tapping began. In particular, the

increment cores were read from the outermost latewood layer (cambium-xylem

interface), to the second and fifth latewood-earlywood margin. These

measurements feature a within-subject experimental control, by comparison of

growth rates before and after the tapping treatment in each tree.


Increment cores were taken from all trees at the Gainesville FL, 1994 site for

measurement of radial growth rates, sapwood thickness, and inside bark radii at

stump height. Wood cores (0.51 x 20 cm) were sampled from positions above and

between opposing borehole clusters (Figure 4.5), at a level slightly above the

boreholes, approximately 15 cm above ground.

Core samples taken with 0.51 x 25 cm increment borer.


core sample
Inner' ",i. ,-


--. I-I -ii -1"1"-'- "

"Above" / Alan Hodges, 2/95
core sample taken 3.8 cm above hole

Figure 4,5. Increment core sampling plan, Gainesville FL, 1994.

Cores taken from the "between" position (Figure 4.5) were examined and

measured with the aid of a dissecting microscope and 0.5 mm ruler. Tree growth

was measured by width of the last 5 year's radial increment on the cores. Resin-

saturated wood noted on the inner part of many cores was taken as evidence of

premature heartwood formation, or tapping-induced resinosis. In other cores, a zone

of incipient heartwood was identified by its characteristic discoloration (Hillis,

1987). The thickness of sapwood was measured from the xylem-bark interface to

this zone of discolored or resin-saturated wood (if any), and tree stem sapwood

areas at borehole level were calculated.

Wood densities in inner and outer portions of radial increment cores were

measured for 18 trees in the April plot, by dividing cores into an outer 114 mm

section, representing wood directly above boreholes (11.4 cm deep), and an inner

section of the remaining length. Cores were weighed (mg) before and after drying in

a forced air oven for 24 h, and green and dry densities were then calculated on the

basis of the original core section volumes.

Extractive analysis of increment core wood samples was done for a small

group of trees (n = 4), to measure monoterpene densities after borehole tapping.

Increment cores were kept frozen to prevent loss of volatile terpenes, then were

extracted in 15 ml pentane, and a 1 ml sample with a 160 ppm para-cymene

internal standard were injected into a Hewlett-Packard gas chromatograph

(HP5890) and integrator (HP3394A). The original volume and dry weights of the

cores were used to calculate monoterpene densities on a whole-tissue basis.

Physico-Chemical Analysis of Oleoresin Produced by Borehole Tapping

Resin from borehole tapping was analyzed for characterization of physical

and chemical properties possibly affecting system behavior. Composite samples

from the McRae (1993) plot were prepared and separately analyzed for 7 groups of

9 to 10 trees receiving each chemical treatment combination of H2SO4 (0, 25%)

and CEPA (0, 5, 10, 15% relative concentration). Physical properties analyzed

included monoterpene and resin acid composition, crystallization, and boiling and

softening points. A rosin crystallization test was done with solid rosin dissolved in

acetone, and timed for appearance of crystals. Analysis of resin acid composition

was done by capillary-gas chromatography, with flame ionization and a methyl ester

internal standard (ASTM standard D 3008). Samples from 67 trees in the


Gainesville FL (1994) experiments were subjected to laboratory analysis to measure

viscosity (#2 rotary viscometer @ 50 deg C) and softening points.

Data Analysis Procedures

Resin yield data for all borehole tapping experiments were combined to

provide increased statistical power for analysis of treatment and resource effects,

and support of systems analysis and modeling. Data were recorded, checked,

compiled, summarized and plotted in Lotus 1-2-3 worksheets (ver. 3.4, Lotus Dev.

Corp, Boston, MA). Simple statistical tests were performed with @STA T, an add-in

software package for Lotus 1-2-3. Freelance Graphics (Lotus Dev.Corp) and

StatMost (DataMost Corp.) software packages were used for plotting data.

Data were further analyzed with statistical model testing and fitting

procedures available from the SAS System (SAS Institute, 1988). The General

Linear Models (GLM) procedure was used to test all main and interactive treatment

effects, and for performing both univariate and multivariate analysis of variance for

within-subjects, repeated-measures experimental designs. The GLM procedure is

convenient for handling both continuous and discrete (class) independent variables.

Differences between treatment means were evaluated with Tukey's test, a

conservative multiple comparison procedure that controls the mean experimentwise

error rate. Dependent variables specified in GLM analyses represented cumulative

hole yields (gm) or tree yields (gm), and derived yield measures expressed on the

basis of time or cross-sectional area tapped (gm/day or gm/cm2).

Response surface analysis (SAS RSREG procedure) was used to determine

the optimal treatment conditions for maximizing yields (SAS Institute, 1988; Box et

al., 1978). The RSREG procedure finds the best-fitting linear model with an

algorithm that rotates the model vector through the experimental design matrix. A

related "ridge analysis" procedure was used to find the set of treatment level values

corresponding to the point of predicted maximum yield on the response surface

(Draper, 1963). Inspection of the matrix of eigenvalues indicated whether the

stationary point was a local maximum or a saddle point.

A least-squares fitting procedure for non-linear models (SAS NLIN procedure)

was used to estimate the parameters for negative exponential models of cumulative

resin flow over time, and area-specific resin yields as a function of tapping

intensity. The procedure required specification of a model regression equation, initial

parameter values, and derivatives of the model with respect to each parameter. An

iterative algorithm (Marquardt method) was used to find the best-fitting model

parameters by regressing the residual sum-of-squares (error) onto the partial

derivatives of the model with respect to the parameters until the estimates

converged, typically within 5 to 10 steps.


Effects of Resource Quality


Borehole resin yields were highly species-dependent. Seasonal yields per

borehole for slash pine (P. elliotth) averaged 657 g (SE = 11 g). Yields were an order

of magnitude lower for most other species tested, including longleaf pine (P.

palustrus) in the southeastern US, Maritime pine (P. pinaster) in Southwestern

France, and Caribean pine (P. caribea var hondurensis) in Venezuela, in spite of

similarly intensive tapping treatments (Table 5.1). Only Pinus oocarpa, a Central

American species showed any promise for borehole production, with yields

averaging 200 g (P. deLarosiere, pers. com).

Table 5.1. Borehole resin yields by species, 1991-1994.
Species Country Average Number
Borehole Boreholes
Yield (gm)
Slash pine (P. elliotti) USA 657 1557
Longleaf pine (P. palustrus) USA 86 20
Caribean pine (P. caribea) Venezuela 40 20
P. oocarpa Venezuela 200 20
Maritime pine (P. pinaster) France 28 297

Resin yields were available for 528 slash pine trees with 1337 individual

boreholes. A plot of the frequency and cumulative distribution of borehole resin

yields is shown in Figure 5.1.


140 -
140 \ Frequency

12 / Percenti le
120 -/ 80%
th \ --

O 100 /- C
0 /
m 80 -/

60 / 4Q0 4%

40 E

20% U

S 0 4 0 8 1 2 1.6 2 0 2.4
Borehole Yield Ckg)

Figure 5,1. Distribution of borehole resin yields, slash pine, 1991-94. Represents
1337 boreholes.

Individual borehole yields ranged as high as 2100 g, with 20 percent producing

more than 1 kg, and approximately 7 percent of boreholes produced less than 100

g. Seasonal yields per tree averaged 1,663 g (SE =46 g), and ranged from zero to

over 8 kg.


Yields for slash pine varied dramatically among the eight sites in Florida and

Georgia, from over 1200 g to less than 500 g per borehole (Table 5.2). The very

high yields at the McRae and Eastman GA sites represented a combination of good

site quality, large trees, and high chemical treatment levels. Yields in the 1994 plot

at McRae GA averaged nearly 2 kg per hole. Yields at the two sites in peninsular

Florida (Gainesville and Waldo) were generally lower than for most other sites in

Florida and Georgia. Yields per hole were lowest of all at the Soperton GA site (443

g), where the very high site quality (SI= 92) and the genetically improved (high


gum-yielding) slash pine stock resulted in rapid timber growth at the expense of

resin production.

Table 5.2. Summary of borehole resin-tapping seasonal yields by site, slash pine,
southeast US. 1991-1994. Means with different letter superscripts were
significantly different (p<.05, Tukey's test)
Site Number of Seasonal Yield (gm)
mean SE CV
Gainesville FL 318 497bc 20 72
Waldo FL 102 552b 32 58
Hosford FL 247 643* 23 56
McRae GA 603 759" 17 55
Eastman GA 20 1233 129 47
Soperton GA 24 443c 66 73
Homerville GA 23 542 87 77
Waycross GA 240 903 na na

Variability in borehole yields was comparable across sites, with coefficients

of variation ranging from 44 to 77. Higher levels of variation were mostly

associated with experimental manipulations rather than inherent site differences.

Tree Size

Tree stem volume was the most important single variable influencing

borehole resin-tapping yields, both in terms of individual holes and whole trees.

Yields for large and very large trees (greater than 27.9 cm) were significantly

greater than small and medium trees, and average yields per hole for very large

trees (over 33.0 cm DBH) were two thirds greater than for small trees (less than

22.9 cm), as shown in Table 5.3. On a whole tree basis, overall yields for larger

trees were of course greater due to a higher number of holes. Tree yields on a unit

hole area basis were greater for large and very large trees. Tree size also interacted

with other treatment effects which significantly affected resin yields.


Table 5.3. Borehole resin-tapping seasonal yields by tree size, slash pine, 1991-

Tree Size (cm DBH) Number
of Bore-

small (less than 22.9) 125
medium (22.9 to 27.9) 376
large (27.9 to 33.0) 454
very large (greater than 33.0) 319
Means with different letter superscripts
Tukey's test).

Seasonal Tree Yield
Yield (gm) Per Unit Hole
mean SE Area (gm/in2)

527" 39 22.8"
551" 18 21.7"
681b 18 25.4b
779c 25 25.9b
were significantly different (p<.05,

Results for 1994 experiments at Gainesville FL, where numbers of holes

were balanced across tree size classes, confirmed the strong effect of tree size and

resin system capacity on resin yields. Large and very large trees produced yields

nearly twice as great as small trees, on both individual borehole and whole tree

bases (Table 5.3). Yields of larger trees were consistently greater across time, with

significant differences appearing at one month after borehole treatment, as shown

in Figure 5.2

Borehole Tapping Treatment Effects

Borehole Diameter and Depth

In general, significantly higher resin yields were obtained for large and deep

holes, and holes drilled at angles displaced from the radial axis. The effect of hole

diameter on yields was investigated with paired 3.49 cm (1.375 inch) and 2.54 cm

(1.00 inch) holes on a total of 35 trees at the Hosford FL, McRae and Eastman GA

sites in 1993. Yields for large diameter holes averaged 996 g compared to 822 g

for the standard 2.5 cm hole (Table 5.4), a statistically significant difference

(p<0.05) by a paired t-test. However, the 21 percent greater yields for larger holes



small (<23 cm)

medium C23 to 28 cm .
r- 600
E large (28 to 33 cm)

>-j 400-----------------
(1) _
>- 400 -,, ... ..- .

ED 200 -

0 20 40 60 90 100 120 140
Days Since Treatment

Figure 5,2. Resin yields over time by tree size, Gainesville, 1994.

were not proportional to their 38 percent greater cross-sectional area. On a

borehole area basis, the yield intensity for the standard borehole diameter (31.9

g/cm2) was 13 percent greater than for the large hole (28.1 g/cm2) (Table 5.4).

Table 5.4. Within-subjects comparison of resin yields for large and regular diameter
boreholes at Hosford FL, Eastman and McRae GA sites, 1993.

Borehole Yield Per Yield Per Unit Hole
Diameter (cm) Hole (g) Area (g/cm2)

Large (3.49 cm) 996 28.1

Regular (2.54 cm) 822 31.9
n = 30 trees

The effect of hole depth on yields was examined with standard 2.54 cm

diameter holes drilled 8.9 to 17.8 cm (3.5 to 7.0 inches) deep. Across all

experimental data, holes greater than 11.4 cm deep produced higher yields (726,

673 g) than shallower holes (456 g). In 1992 experiments with systematic


manipulation and within-subjects controls at the Waldo and Hosford FL, and McRae

GA sites, hole depths were examined at levels of 10.2, 14.0, and 17.8 cm. Again,

yields for the two deeper hole groups (726, 776 g) were significantly greater than

the shallowest hole (640 g), as summarized in Table 5.5. However, yields on a unit

area basis were highest for the shallow holes (24.8 gm/cm2), and lower for the

medium and deep holes (20.3 and 17.2 gm/cm2).

Table 5.5. Borehole yields by depth, Waldo and Hosford FL, and McRae GA sites,
Borehole Depth Avg. Yield Yield Per Unit
(cm) (gm) Hole Area
Shallow (10.2 cm) 640b 24.9
Medium (14.0 cm) 726a 20.3
Deep (17.8 cm) 776" 17.2
Different superscripts indicate significantly different mean
yields (p<.05).

Results in Gainesville (1994) experiments with hole drilling depths

manipulated at very wide levels (8.9 vs. 17.8 cm) showed that yields for deep

holes were substantially greater than shallow holes (Table 5.6). Moreover, within

each treatment group, yields of shallow experimental holes were 109 g less than

their control holes (406 vs. 515) compared to a difference of only 23 g between

deep experimental holes and their respective controls. Yields for control holes were

greater in trees with deep experimental holes, possibly due to the closer proximity

between opposing holes in this case.


Table 5.6. Within-subjects comparison of borehole yields by hole depth, Gainesville
FL, 1994.
Experimental Average Seasonal Yield per Difference
Borehole Depth Number Borehole (gm) Control -
(cm) of Trees Experimental Control Holes Exp (gm)
Holes (8.9 cm)
Shallow (8.9) 44 406 515 -109*
Deep (17.8) 24 580 603 -23
Significant by paired t-test (p<0.05).

In summary, variation in both dimensions of hole areal extent (diameter and

depth), were associated with higher yields, indicative of the greater capacity of

resinous wood tapped, but the higher yields were not proportional to their greater

area, as reflected by the diminution in yields per unit area. These findings are

consistent with observations of yields as a function of wound size in conventional

gum resin production operations (Snow, 1954), and support the hypothesis that

pressure potential for resin exudation is reduced for larger boreholes.

Hole Orientation

Borehole yields by horizontal orientation with respect to the radial axis of the

tree, are shown in Table 5.7. Yields for holes drilled at an angle of 45 degrees (735

g) were significantly higher than for radial holes (640 g; p<.05, Tukey's test).

Moreover, yields for angled holes were increasingly greater at larger hole depths,

and at depths of 17.8 cm, yields for tangential holes were over twice as great

(Table 5.7). This pattern of results reflects the different compartment areas of the

tree stem that are tapped by radial and tangentially oriented holes, and is consistent

with the predicted sink effect of incipient heartwood in the core region of the tree.

Table 5.7. Borehole yields by horizontal orientation, Waldo and Hosford FL, and
McRae GA sites, 1992.
Hole Orientation with Number Average Borehole Yield (gm)
respect to radial axis of Holes All Hole 10.2 14.0 17.8
All Hole 10.2 14.0 17.8
Depths cm cm cm
depth depth depth
Radial (0 deg) 267 640 635 680 363
Angled (45 deg) 426 735 653 743 807

In 1994 experiments at Gainesville FL, hole orientation in the vertical plane

was examined by boring at a downward angle of approximately 45 degrees from

the horizontal plane. Average yields for downward holes were significantly greater

than horizontal holes (544 vs. 439 g), according to a univariate statistical test

(p<.05). A within-subjects analysis comparing yields against the control hole

revealed a difference of only 6 g (-42 vs. -48 g, Table 5.8), suggesting that

downward holes enhanced yields for the opposing control hole.

Table 5.8. Borehole yields by vertical orientation, within-subjects comparison,
Gainesville FL, 1994.
Experimental Hole Average Yield per Yield
Vertical Orientation Number Borehole (gm) Difference
(degrees from of Trees Control -
horizontal plane) Experimental Control Exp (g)
Holes Holes Exp (gm)
Downward (45 deg) 21 544 586 -42
Horizontal (0 deg) 59 439 488 -48

Spacing Among Clustered Boreholes

Clustered borehole spacing patterns were studied for their effects on yields

in two different experiments. At the Hosford site in 1993, holes were installed in

three different patterns, illustrated in Figure 5.3: two new holes paired together

approximately 10.2 cm apart ("paired"), holes evenly spaced around the tree's


circumference and midway between previously drilled holes ("evenly spaced"), and

holes offset approximately 10.2 cm from a previous season's hole ("offset").

Paired Evenly spaced Offset

... ... 10 2 cm

New Hole (2nd year Old hole (1st year)

Figure 5,3. Borehole spacing patterns investigated, Hosford FL (1992-1993).
Trees received same number of holes (10.2 cm deep) and same chemical
treatment in two consecutive years.

As shown in Table 5.9, average yields for the "evenly spaced" and "offset"

conditions did not differ (582 vs. 595 grams per hole), while the "paired" holes

produced substantially less (430 grams). Although these differences were not

statistically significant because of high variability, the direction of the results

suggested that spacing between holes did affect resin yields.

Table 5.9. Resin yields by hole spacing pattern, Hosford FL site, 1993.
Hole Spacing Number Yield Per Yield Per Hole
Pattern* of Holes Borehole Per Day
(grams) (grams)
Paired 24 430 2.16
Evenly-spaced 41 582 2.93
Offset 30 595 2.99
Refer to Figure 5.3 for definitions of spacing patterns.


Experiments at Gainesville (1994) were designed with more levels of spacing

treatments, with clusters of 2 or 3 holes made at "narrow" and "wide" horizontal

separations between outer drill centers, resulting in four different combinations of

hole numbers and spacings between adjacent holes, as previously described in

Figure 4.2. These spacings were specifically selected to correspond to the extreme

settings of the multi-spindle drill head adopted for mechanization of drilling

operation, discussed in the final section. Results of this experiment are presented in

Table 5.10. The effect of the treatment in each case is gauged by a within-subjects

comparison of yields between the experimental and the single control boreholes. In

general, yields for each hole varied consistently as a function of distance from other

holes. In all cases, the control hole ("back position") produced a significantly higher

yield than the average of the set of 2 or 3 holes on the opposite side of the tree

("left", "right", or "center" positions). Groups of two holes spaced 6 inches apart

had essentially the same yields as control holes (465 vs 470 g), while groups of

two holes spaced 9.53 cm had somewhat lower yields compared to controls (560

vs 616 g, Table 5.10).

Table 5.10. Resin yields for different numbers and spacings of clustered boreholes,
Gainesville FL, 1994.
Experimental Condition" Number Total Average Seasonal Yield Per Hole (gm)
of Trees Hole
Group Control Experimental Holes (2 or 3)
Yield Hole
Number of Vertical Horiz. (gm) All Outer Center
Clustered Spacing Spacing Holes Holes Hole
Holes (in) (cm)
3 0 4.78 11 1163 525 387 445 314
3 0 7.62 11 1181 534 394 405 371
2 0 9.53 21 1121 616 560 na
2 0 15.20 41 929 470 465 na
3 1.88 4.78 15 1827 na 612 591 645
All Conditions 99 1289 522 502 493 460


Groups of three holes at both the 7.62 and 4.78 cm spacings had

substantially lower yields compared to their control holes. Also, within groups of 3

holes, the hole in the "center" position produced lower yields than the outer holes

("left" or "right" positions), except for trees with 4.78 cm vertical spacing (Aug

plot), where center hole yields were the highest at this site (645 g). Trees in this

plot (Aug) were drilled by the mechanized drilling system with vertically offset

boreholes, in the pattern shown in Figure 7.1. Total yields for groups of 2 or 3

experimental holes varied from 900 to over 1800 g, and differed significantly only

on the basis vertical spacing, not on horizontal spacing or number of holes.

The general yield depression effect as a function of hole number and spacing is

evidence of mutual competitive interference between closely spaced holes,

consistent with the hypothesis of a localized common source of resin in the tree,

and the existence of a pressure potential effect as a function of tapping intensity.

The higher yield of the center hole when there was a vertical separation may be

attributed to increased xylem water potential, chemical stimulation, or reduced

capacity interference in the zone around these holes, below the two outer holes.

Vertical separation of boreholes is an opportunity to overcome the yield depressing

effects of hole clustering envisioned for mechanized systems.

Chemical/Biological Treatment Effects

Treatments with 2-chloroethyl phosphonic acid (CEPA) affected borehole

resin yields consistently and significantly across all experiments during 1991-94.

CEPA levels greater than .05 ml a.i. per hole produced yields averaging 643 to 722

g compared to 352 to 360 g for the lowest treatment level or no CEPA (Table

5.11). CEPA treatments also significantly affected yields on a whole-tree basis,

with yields for the trees receiving any CEPA treatment 3 to 4 times greater than for


trees with no CEPA treatment. Thus, CEPA appeared to have both localized and

systemic effects, and to have a threshold level for enhancing yields.

Table 5.11. Borehole resin yields by CEPA treatment level, 1991-1994.
CEPA Dose (ml/hole) Number Cumulative Final
of Yield (gm)
Mean SE

none 97 352b 27
low (<.05) 20 360b 50
medium (.05-. 10) 458 643" 17
high (.10-.15) 461 7068 20
very high (>.15) 301 722a 25

Different superscripts indicate significantly different means
(p<.05, Tukey's test).

To resolve whether higher levels of CEPA treatment resulted in

proportionately higher yields, data were separately analyzed for 1994 experiments

where CEPA dosages were more widely varied, the chemical treatment was applied

more precisely with a fixed-displacement type sprayer, and a within-subjects

contrast was available from the control hole. Results of 1994 experiments by

CEPA treatment are summarized in Table 5.12. Experimental holes with equal or

higher CEPA levels than control holes (.05 to .07 ml a.i.) had yields comparable to

the controls, while those with lower CEPA levels had significantly depressed yields.

Thus, these results confirm that a threshold dosage of about 0.05 ml CEPA per hole

was sufficient to produce good yields, but there was marginally less effect at higher



Table 5.12. Borehole resin yields by CEPA treatment level, within-subjects
comparison, Gainesville FL, 1994.
CEPA Dose Experimental Number Cumulative Final Yield (gm)
Hole compared to control of Trees
hole dose of 0.07 ml) Experimental Control Difference
Holes Hole
lower (0.035) 8 363 690 -327
equal (0.070) 51 472 479 -7
higher (.14 to .16) 21 455 525 -70
very much higher (.28) 4 718 725 -7

Sulfuric acid had widely variable and mixed effects on borehole tapping

yields, which were confounded with site, year, and plot effects. Average yields for

high dosages of sulfuric acid did not significantly differ from average yields for no

acid, but acid treatments strongly interacted with CEPA treatments. Since both

CEPA and sulfuric acid are strong acids, it is reasonable that their effects were

complimentary in altering the chemistry of the borehole wound environment for

breakdown of CEPA into ethylene.

Experimental boreholes which received treatment with a sterilized culture

extract of the Blue stain fungus (Ophiostoma) had lower average yields than those

without (372 vs 479 g, n= 30), but according to a within-subjects analysis, there

was no effect of extract treatment. The positive effect of this treatment on resin

flow reported by Popp et al. (1991) was over a short time period of 2 days.

Effects of Collection Container Type

To measure the effect of reduced container pressure on yields, a controlled

study was performed in 1994 at McRae GA, from August 2 to November 9 (99

days), with each of 21 trees receiving 2 boreholes treated uniformly (10.2 cm

depth, radial orientation, 7.5% CEPA) except that one borehole was fitted with a 2-


liter PET bottle while the other had a spout-bag device installed. The average yield

for boreholes with a spout-bag device (1173 g) was 19 percent greater than yields

for holes with bottles (983 g) (Table 5.13).

Table 5.13. Borehole yields collected in 2-liter PET bottles and spout-bag apparatus,
McRae GA, 1994.
Container Seasonal Yield (gm)
Mean SE
2-liter PET bottle 983 57
spout-bag apparatus 1173 77

This difference was highly significant according to a paired t-test (p<.01). The

magnitude of this effect may have been emphasized by the generally very high yield

levels of these trees, which resulted in many of the 2-liter bottles becoming nearly

filled, so that a high pressure was developed in the bottles.

This experiment showed that pressure potential can affect yields from

borehole tapping, since this was the only variable that differed for the two

container types. The average volume of resin collected in bottles was calculated at

923 cc (at a resin density of 1.065 gm/cc), leaving a gas headspace of 1077 cc in

the 2 liter bottles. This represented a 1.86 compression ratio of the headspace gas

in the bottle (2000/1077 cc), or a pressure of 1.86 atmospheres, assuming no

leakage occurred. The relative system sensitivity, in terms of rate of change in yield

(190/1173 gm) with respect to the change in pressure (.86/1.00 atm), was 19


Effects of Time of Year

Cumulative final yields for separate plots established at the Gainesville site in

1994 are plotted in Figure 5.4. Yields generally followed the annual heating cycle,

and peaked in the August

plot. Table 5.14 600 -

summarizes seasonal -
k-) Ao. 21
effects of borehole wo -

tapping. Borehole yields 300 -
in the plot established in b 2oo

August were significantly 100

higher than for the other 100 150200 250
Jul ian Day of Treatment
three phases, which did
Figure 5,4. Resin yields by Julian date of treatment,
not differ. This result is Gainesville, 1994.

consistent with observations of conventional resin production, with peak yields

obtained during July and August (Clements, 1961; Harper and Wyman, 1936).

Higher yields for the August plot were also associated with the yield-enhancing

effect of the 4.8 cm vertical offset between the center and outside holes, as

discussed previously.

Table 5.14. Borehole resin yields by time of year installed, Gainesville FL, 1994.

Borehole Yield Tree Yield
Time of Year Installed Num (gm) Num (gm)
(experimental plot) Holes Mean SE Trees Mean SE
Mean SE Mean SE

April 21 to Oct. 15 60 464b 38 20 1393 161

June 23-25 to Nov. 27 144 474b 33 44 1552 152

August 21-25 to Dec. 31 44 608" 54 15 1827 232

September 8 to Dec. 31 70 502b 34 20 1758 188
Different superscripts indicate significantly different mean yields (p<.05,
Tukey's test).

Weather patterns during the period of this experiment did not account for

the differences in yields between plots in a predictable fashion. Average daily


temperatures during the first month following borehole treatment were higher for

the June plot (27.0 deg C) than the August and September plots (25.7, 24.4 deg

C), while rainfall was higher for the September plot (0.43 cm/day) than the June or

August plots (0.18, 0.28 cm/day). This suggests that differences in inherent

seasonal resin productivity and treatment effects were responsible for the yield

differences observed among plots.

Yields for A Second Year of Production

Trees tapped for two consecutive seasons at the Hosford site (1992-93)

with identical treatments and numbers of holes resulted in slightly lower average

yields in the second year. As shown in Table 5.15, average yield per tree declined

13 percent, and average yield per hole declined 17 percent. These differences were

statistically significant with a paired t-test (p<.05). These results are evidence of

alteration in the capacity for resin production by borehole tapping, and suggest that

long-term borehole tapping with a series of treatments may suffer from reduced

yields in latter years.

Table 5.15. Yields for borehole tapping trees in two consecutive seasons, Hosford
FL, 1992-1993.
Year Yield Per Yield Per Yield Per Hole
Tree Hole Per Day
(grams) (grams) (grams)
1992 1614 642 5.49
1993 1407 535 2.69

n = 37 trees


Resin Flow Rates Over Time Since Treatment

Cumulative resin yields over time in 3 plots at Gainesville FL (1994), at 7

days, 23 to 28, 50 to 51, and 99 to 147 days following borehole treatment, are

summarized in Figure 5.5.
The higher average yields 23-25
600 -<
Aug 22-25
for the August plot -

(Table 5.14), were ,--4 .
400 -

evident within 28 days 300 -

after borehole treatment, 200 -
m /
and were maintained for 1oo -

the rest of the 0 20 4o ED so 100 120 140
Days Since Treatment
experiment. The duration
Figure 5,5. Cumulative resin yields over time for
of resin flow observed experimental plots at Gainesville FL (1994).

for borehole tapping was several-fold longer than typically occurs for conventional

open-face production methods, and is a key to the higher productivity of this

system, just as prolongation of flow was a key innovation for acid paste treatments

in conventional gum resin production.

All data for resin yields over time are plotted in Figure 5.6, expressed as a

percentage of the final cumulative yield. The exponential function plotted in Figure

5.6 was fitted to the data by least-squares regression (SAS Inst., 1988) using the

model shown in Equation 5, where Yt(days) is the cumulative yield measured at time

t=days, YF was the cumulative final yield, and -0.0189 was the fitted parameter.


100% 2 0%

Cumulative Flow

80 Flow Rate
80% \

LL 60% -

1.0% --

S40% \ 4J

u p
20% -

0% I 1 I J I I I ...- ...- -- 4- 0. 0%
0 20 40 60 80 100 120 140 160 180 200 220 240
Days Since Treatment

Figure 5,6. Plot of cumulative resin flow and flow rate over time since treatment
(days), expressed as a fraction of final cumulative flow, Gainesville FL, 1994.

Yt= Yx(1 ---.018'" (5)

This regression model explained 92 percent of variation in cumulative resin

flow over time as a share of total flow (r2=.922, n= 914), given that the total flow

was known. The time constant for this function, the point at which two-thirds of

the final flow had been reached, calculated as the inverse of the exponential

parameter, was 53 days. The equation predicts that 90 percent of total flow was

reached at approximately 120 days, and 95 percent at about 180 days. The high

reliability of this flow rate function, is noteworthy, and is confirmation of the

capacitance and pressure potential source-limited nature of the borehole resin


production system. The rate of daily resin flow over time is shown in Figure 5.6 as

a percentage of final flow.

An expression for the instantaneous rate of flow is represented by the first

derivative of the fitted equation for cumulative flow as a function of days is shown

in equation 6, with terms the same as defined previously (equation 5).

--.0189x YFx(1 -e -.o9xDa) (6)

This flow rate 0 025

function represents the 0 0
S 0 .0 20 .. .... .. . . . ... .. .
marginal value of resin

production over time. A 0o 015

marginal value function L
0 0
over time is plotted in a
0 005... .- ........... ...
Figure 5.7 for an

expected tree yield of 0 1
0 20 40 60 80 100 120 140 160 180 200 220 240
2.0 kg and a product Days Since Treatment
Figure 5,7. Marginal value function for resin flow over
value of $.60 per kg. time.

This example shows that for a daily cost of $.005 for use of the tree, the optimal

production period is about 80 days. A higher yield level or product price would shift

the curve to the right, resulting in a longer optimal production period.

All experimental treatment and resource quality effects previously noted for

seasonal resin yield results were also present in the intermediate time yield results.

A repeated measures analysis of variance on cumulative resin yields at each period

showed significant effects for hole vertical orientation, tree size and tapping

intensity (F test, p<.05).


The exponential-decay time function for resin yields was separately analyzed

and fitted by non-linear least-squares regression for subgroups of data. Results for

the three experimental plots in which time-course measurements were made, are

presented in Table 5.16. Plots established later in the season (August and

September) had relatively more rapid initial flow and rapid decay, indicated by

higher estimated values for the exponential function coefficient, and

correspondingly lower values for the number of days to achieve two-thirds of total


Table 5.16. Parameters and statistics obtained for non-linear least squares analysis
of cumulative resin flow over time, Gainesville FL, 1994.
Experimental Exponential Days to Number of Model
Plot function achieve Observations Coefficient of
(Date) Parameter 67% of Determination
Estimate (eq.5) total flow (r2)
June 21 0.0176 56.9 572 .920
August 24 0.0200 50.0 132 .915
September 8 0.0207 48.3 210 .936
All 0.0189 52.9 914 .922

High initial flow rates and rapid decay were associated with shallow rather

than deep hole depths and horizontal rather than downward-oriented holes. The

slower flow response of downward holes is partly attributed to the necessary hole-

filling volume required before external flow occurs. Chemical treatment levels

affected flow rates, with higher CEPA levels bringing about a prolonged flow, as

well as increased total yield.

Yields by Compartment Area

Yields per unit tree cross sectional area were analyzed separately for "hole",

"outer", and total "sector" compartment areas. Over all data from 1991-94,


borehole yields averaged 8.5 g cm-2 of tapped sector area, 22.9 g cm-2 hole area,

33.9 g cm-2 outside area, and 42.3 g cm-2 inner area. Results for resin yields

expressed on a unit area basis generally showed the same pattern of treatment

effects as did the raw data for borehole yields, but a somewhat different pattern for

experimental sites, due to corrections for tree size as a confounding variable across

sites. Yield per unit sector area and outer area were significantly higher for the

Hosford site, while yields for the Gainesville and McRae sites were not significantly

different, as shown in Table 5.17.

Table 5.17. Borehole resin yields per unit compartment area, by site, 1991-94.
Experimental Site Num Yields Per Unit Area (gm/cm2)
Sector Area Hole Area Outer Area

Mean SE Mean SE Mean SE

Gainesville FL 318 7.3b 0.3 19.8ab 0.8 28.2bc 1.7
Waldo FL 102 5.0O 0.5 17.1b 1.1 20.2c 1.9
Hosford FL 247 11.9a 0.5 24.1" 0.8 49.48 2.0
McRae GA 603 8.2b 0.3 24.6" 0.6 33.3b 1.9
Soperton GA 24 8.8b 1.2 18.4b 2.6 27.4bc 4.5
All sites 1337 8.5 0.2 22.9 0.5 33.9 1.1

Superscripts indicate significantly different means (p<.05, Tukey's test).

Analysis of Tree Tapping Intensity

Borehole yields per unit compartment area were analyzed in relation to tree

tapping intensity, calculated as the ratio of borehole sector area to tree basal area.

Area-specific yields generally declined with increasing tapping intensity, as shown

in Table 5.18. Yields for low and medium tapping intensities (less than 30%) were

significantly higher than yields for high or very high tapping intensities (greater than


30%). These results support the conclusion that resin flow pressure potentials are

inversely related to the extent of borehole tapping treatments.

Table 5.18. Borehole resin yields per unit compartment area, by tree tapping
intensity, slash pines, 1991-94.
Tree Tapping Intensity Num Yields Per Unit Area (gm/cm2)
(sector area tapped/tree Holes
basal area, cm2/cm2) Sector Area Hole Area Outer Area

low (less than 15%) 367
medium (15 to 30%) 277
high (30 to 45%) 375
very high (over 45%) 255

Superscripts indicate significantly
(p<.05, Tukey's test).

Mean SE Mean SE Mean SE

13.6" 0.5 27.9" 1.0 58.98 2.8
9.1b 0.3 24.3" 1.0 33.9b 1.7
5.7C 0.2 20.5b 0.6 21.4c 1.0
4.5C 0.2 17.1b 0.6 16.4c 1.0

different means within experimental condition

Yields per unit area were analyzed as non-linear functions of unit area, using

the model shown in equation 7, where YA is the cumulative yield per unit area

(gm/cm2), and the parameters Bo and B, were fitted by least squares regression.

YA=BO (-BxA)e

The function for expected hole yields per unit sector area tapped as a

function of sector area tapped, is plotted in Figure 5.8 along with upper and lower

95 percent confidence intervals. This model had a coefficient of determination of

71 percent (r2=.710).

Borehole yields were predicted from this relationship as the product-moment

of the extensive variable (sector area tapped) and the intensive variable (expected

hole yield per unit sector area), resulting in a bitonic function with a peak borehole

yield of about 775 g at about tapping extent of 110 cm2 of tapped sector area. This

implies that tapping an area too large results in reduced yields.


E Expected value

E Upper 95% C -I
20 .

Lower 95% CI


0) \ .
S10 -

0 0


S o I0 I I I I I
6.45 38.7 70.95 103.2 135.45 167.7
Sector Area Tapped Ccm^2)
Figure 5,8. Borehole resin yield intensity per unit sector area (gm/in2), and
predicted hole yield (gm) as a function of sector area tapped (in2), 1991-94.

Expected hole yields per unit area of "hole" and "outer" compartments

showed similar exponentially declining trends as a function of unit areas. Model

parameters and statistics for all yield per unit area analyses are summarized in Table

5.19. Predicted hole yields as a function of hole area tapped were monotonically

increasing over the range of experimental data, peaking at 45 cm2, corresponding to

hole depths of 17.8 cm.

Table 5.19. Model parameters and statistics for borehole yields per unit area
(g/cm2) as a non-linear function of unit area (cm2), slash pines, 1991-94.

Compartment Parameter Value Coefficient of
Area (eq. 7) Determination

Bo B1 (r2)

Sector Area 19.4 0.0093 .710

Hole Area 36.1 0.0155 .716

Outer Area 138.7 0.0713 .639


Borehole yields per unit area were also analyzed as a declining exponential

function of tapping intensity, defined as the fraction of tree cross-sectional area

tapped. These analyses generally resulted in narrower confidence intervals, and

slightly larger coefficients of determination (Table 5.20). The model based on sector

area predicts a maximum borehole yield of about 0.74 gm/cm2 of tree area tapped

at a tapping intensity of about 11 percent of the tree cross-sectional area.

Table 5.20. Borehole yield intensity per unit area (g/cm2) as a function of tapping
intensity index (cm2/cm2), non-linear model parameters and statistics, 1991-94.
Compartment Area Parameter Value Coefficient of
Bo B1 (r2)

Sector Area 19.8 1.502 .719
Hole Area 30.1 0.439 .728
Outer Area 116.4 2.528 .600

Resin yields were analyzed in similar fashion on a whole-tree basis,

representing the sum of all borehole yields and tapped compartment areas, with

results similar to those obtained on an individual borehole basis. Tree resin yields

per unit sector area tapped are plotted as a function of tree tapping intensity in

Figure 5.9. A declining exponential function fitted to these data had a coefficient of

determination of nearly 75 percent (r2= 0.749). The fitted curve for yield per unit

sector area as a function of tapping intensity is shown in Figure 5.10. The predicted

borehole yield per unit tree area (gm/cm2) plotted in Figure 5.10 (right axis) was

calculated as the product moment of tapping intensity (horiz. axis) and expected

yield per unit sector area (left axis). This function for tree yield per unit sector area

tapped predicts a yield of about 7.0 gm/cm2 at an optimal tapping intensity of about

30 percent of tree stem area.


I I 4 14

0% 10% 20% 30% 40% 50% 60% 70%
Sector Area Tapped / Tree Area Ccm^2/cm"2)

Figure 5,9. Tree resin yields per unit sector area tapped as a function of tree tapping

intensity, borehole-tapped slash pines, 1991-94, plotted with numbers representing

tree sizes (1, 2, 3, 4), from small to large, respectively.

20 \


10 -

0.01 0.11 0 21 0 31 0 41
Tree Sector Area Tapped/Tree Stem Area

2 5





o o

Mean Tree Yield/Sector Area Upper 95% Cl Lower 95% Cl Tree Yield/Tree Area

Figure 5,10. Tree resin yields per unit sector area borehole-tapped (expected value

+/- 95% confidence interval), and predicted total tree yield as a function of

tapping intensity.


3 4

4 13

80% 90%


Response Surface Analysis and Treatment Optimization

Response surface analysis of borehole resin yields on a whole-tree basis with

respect to tapping intensity and CEPA dosage (combined for all holes) resulted in a

model with a moderately high coefficient of determination (r2 =0.425, df =483).

Linear, quadratic, and crossproduct terms in the model were all statistically

significant (F test, P<.05).

Ridge analysis of the response surface with respect to tree sizes showed

that treatments which produced maximum yields differed only slightly, as shown in

Table 5.21, indicating a relative insensitivity of yields to treatment levels near the

optimum. CEPA treatment levels were somewhat more sensitive, with the optimal

dosage ranging from 0.36 to 0.48 ml (a.i.) for small to large trees, 23 to 36 cm dbh

(9 to 14 inches). Because expected tree yields were not very sensitive to deviations

from the optimal tapping intensity, a uniform tapping treatment for the range of tree

sizes likely to be encountered in a forest stand will probably result in tapping

intensities that robustly produce near-optimal yields.

The predicted tree yields for the optimal tapping treatments are generally

higher than predicted by the non-linear model shown in Figure 5.10, due to the

global optimization performed by the ridge analysis procedure, but are within the

range of experimental data.

Table 5.21. Predicted treatment levels for maximizing tree yields as a function of
tree diameter, from ridge analysis of response surface, slash pines, 1991-94.
Tree Diameter (DBH) Optimal Treatment Level Estimated
Tree Yield
inches cm CEPA Tapping intensity (gm)
dosage (sector area
(ml/tree a.i.) tapped/tree area)
9.0 22.9 0.360 0.420 1520
9.6 24.4 0.359 0.424 1670
10.1 25.7 0.362 0.426 1817
10.7 27.2 0.369 0.425 1963
11.3 28.7 0.380 0.422 2112
11.8 30.0 0.393 0.419 2263
12.3 31.2 0.408 0.416 2419
12.9 32.8 0.424 0.409 2579
13.4 34.0 0.441 0.404 2745
13.9 35.3 0.459 0.398 2916
14.4 36.6 0.477 0.392 3093

Productivity Comparisons With Traditional Systems

Because borehole tapping is a fundamentally new method of gum resin

production, it is appropriate to compare its productivity with traditional systems.

Table 5.22 summarizes typical yields, treatment frequencies and yields per

treatment reported for various production systems with slash pine in the Southeast

US. For a typical tree (25 cm dbh), yields from wood chipping and bark chipping

methods ranged from 3.7 to 7.3 kg annually, for 8 to 33 treatments. The predicted

yield from a single borehole tapping under optimal treatment conditions (1.8 kg),

represents a yield per treatment nearly twice as great as the bark chipping method

with acid-CEPA paste treatment (1800 vs 918 g, Table 5.22). Thus, the borehole

resin production system offers significantly greater labor productivity than

traditional systems, but sacrifices overall tree productivity for extended production


Table 5.22. Average yields, number of treatments, and yield per treatment for
different resin collection systems with Slash Pine in the Southeast US.


Treatment method

Tree Yield

Number of
per year


Yield per

Wood 1.27 x 1.27 cm streaks 3.68 33 7 111
chipping1 1/3 circumference
Bark 50% H2SO4 spray, 1.9 cm 5.33 17 14 314
chipping2 streaks 1/3 circumference

Bark 50% H2SO4 and 15% 7.34 8 28 918
chipping3 CEPA paste, 3.8 cm
streaks 1/3 circumference
Borehole 3-2.5 x 10 cm holes, .36 1.80 1 na 1800
tapping ml CEPA

Yields represent 25 cm DBH trees.
' Harper and Wyman, 1936; Schopmeyer and Larson, 1955
2 Bengston and Schopmeyer, 1959
3 McReynolds and Kossuth, 1984


Effects on Tree Growth

Average annual radial growth rates of borehole-tapped trees and matched

untapped controls (McRae 1992 plot) did not substantially differ during a 2-year

period since tapping (Table 6.1). Tapped trees had slightly higher overall growth

rates both before and since tapping, and both groups had greater growth during the

latter 2 year period than the prior 3 year period, but the acceleration in growth

since tapping was equal (30%) for both groups. These trees were tapped from July

to October, a period when growth effects of resin production have been reported

most marked (Schopmeyer and Larson, 1954). These results indicate that borehole

tapping on this above-average quality site (Sl = 84) did not adversely affect tree

growth rates during this particular period when growth rates were relatively good. It

is possible that a growth reduction due to tapping could be observed at times of

less favorable growing conditions, or on extreme sites.

Table 6.1. Annual radial growth rates of borehole tapped and non-tapped slash
pines, before and since tapping, McRae GA, 1989-1993.
Average Annual Radial Increment (mm)

Growth Period Tapped Trees Control Trees
(n=41) (n=25)
Mean SE Mean SE
Before Tapping (3 yrs, 1989-91) 2.73 0.16 2.49 0.18
Since Tapping (1.7 yrs, 1992-93) 3.55 0.17 3.25 0.20
Change 0.82 0.10 0.76 0.05


Tree radial growth was inconsistently correlated with borehole yields. For

the trees tapped in the McRae (1992) experiment, 5 year growth was negatively

correlated with borehole yields (r = -22%). In Gainesville (1994) experiments,

growth was moderately positively correlated with resin yields (r = 32%), but this

relationship was confounded by the correlation between tree size and growth rates.

Tree Stress Effects

Minor browning and leaf loss occurred in approximately 5 percent of

borehole tapped trees during experiments from 1991 to 1993, generally associated

with high levels of CEPA treatment. Some defoliation of the canopy was observed

in 85 percent of trees in the April plot at Gainesville (1994). Three trees (15%)

were completely defoliated and two later died, while most others that suffered less

than 50 percent defoliation generally recovered. Trees in this plot were the earliest

that had ever been tapped in the springtime, and received a rather high dose of

CEPA (.45 ml), though not greater than many other trees in later plots. The

seasonal effect of CEPA-induced tree stress is probably a function of more rapid

uptake and translocation of the chemical to the tree's canopy during the period of

rapid growth between March and May in the southern US. CEPA chemical levels for

borehole treatments during this period should be reduced to minimize excessive

stress effects. Defoliation was more severe for smaller trees, presumably because

they have less buffering capacity against chemical treatments.

Attacks by Black Turpentine beetles (Dendroctonus terebrans) were also

much more severe during 1994 than at any previous time. As many as 15 separate

beetle attacks (pitch tubes) were counted on individual trees. BTB attacks were not

clearly associated with CEPA-induced stress levels, but were most intense near the

edges of plots, where beetles were intercepted as they moved into the stand. Some


attacks by Ips beetles were also observed, and in all cases resulted in tree death. It

is possible that the unprecedented level of insect attacks observed in 1994 were

related to greater emissions of attractant terpenes from the spout-bag collection

devices than from the PET bottles.

Observations of defoliation and beetle attacks were summarized as a

composite rating of tree stress, with 3 levels: "severe" for trees with over 30

percent defoliation, more than 5 BTB attacks, or Ips beetle attack; "moderate" for

trees with 1 or 2 BTB attacks or up to 30 percent defoliation; and "none". Resin

yields were significantly different for these tree stress categories as shown in Table

6.2. Yields for ostensibly unstressed trees were nearly 3 times greater than for

severely stressed trees.

Table 6.2. Summary of borehole resin yields by tree stress level, Gainesville (1994).
Tree Stress Category Number Avg. Borehole Avg. Tree
of Trees Resin Yield Yield (gm)
None: no BTB attacks, no defoliation, 41 592" 1878"
no Ips attacks
Moderate: up to 5 BTB attacks or up 50 474b 1514b
to 30% defoliation, no Ips attacks
Severe: 5 or more BTB attacks or 8 216c 664c
over 30% defoliation, or Ips attack.
Superscripts indicate significantly different means (p<.05, Tukey's test).

It was observed that BTB attacks often resulted in a rapid reduction in resin

flow rates. A within-subjects, repeated measures analysis of variance (SAS GLM)

indicated that incidence of BTB attack was a highly significant factor affecting resin

yields over time (p<.001). Figure 6.1 shows that resin yields for severely stressed

trees were nearly equal to less stressed trees during the first month after treatment,

but flow rates were reduced during the second and third months. This result is

consistent with other reports of reduced oleoresin flow and oleoresin exudation

pressure in trees under
severe stress from
500 moderate
drought or insect attack.
40 --------- .. ----
There was no evidence, _
>- 300 -
however, that moderate _-
200 -
levels of stress, indicated L o

by some defoliation or 100

beetle attack, resulted in o0 1 1 0 -
Days Since Treatment
greater yields as
Figure 6,1. Borehole resin yields over time, by tree stress
predicted. level, Gainesville, 1994.

Tree mortality due to borehole tapping has generally been very low, with less

than 1 percent dying for any reason during 1991-93 studies. At the Gainesville site

in 1994, 3 of 20 trees (15%) in the April plot eventually died as a result of severe

defoliation due to CEPA treatment, and subsequent attack by Black Turpentine

Beetles and Ips beetles. This was the highest mortality observed to-date, and is

probably representative of extreme environmental conditions. The Gainesville area

suffered an unprecedented epidemic of the Southern Pine Beetle that killed a

substantial part of the urban pine forest in 1994.

Deposition of Extractives

Deposition of extractives in the tree stem due to borehole tapping not only

provides insight to the mechanisms of borehole resin flow, but is important for

subsequent utilization of the wood. A small sample of trees were sacrificed and

sectioned at regular intervals to examine and photographically document the pattern

of resin deposition around boreholes. Figure 6.2 shows the extent of resin

deposition around boreholes in a tree which had been tapped with two boreholes.

Resin soaking occurred

approximately 0.5 to 1.0 Transverse view

cm around the margins of

holes in a horizontal
.angled hole
plane. For the hole drilled radial ho I.

at an oblique angle with

respect to the tree's

radial axis, resin soaking

also extended
Figure 6,2. Illustration of resin deposition around radial
horizontally from the hole and angled tapholes. Cross section at hole level.

to the tree's center in a pie-shaped sector and extended vertically about 75 cm

above the hole, but not below. This demonstrates that borehole tapping can cause

extensive resin deposition in the tree, although the incidence of this phenomenon is

unknown. The yield from the hole with extensive resin deposition was significantly

less than for the opposing hole, suggesting that resin in this part of tree was

diverted into a low pressure sink. The greater vertical extent of resin deposition is

consistent with the patterns described by Shigo (1979), and suggests that

cavitation of the water conducting pathways occurred above the taphole. The time-

course of resin deposition is not known, or whether significant resin flow occurs

after deposition.

Green and dry wood densities for inner and outer portions of radial increment

cores measured for 18 trees are summarized in Table 6.3. The outer section of

cores from above boreholes had a significantly higher density than their

corresponding inner sections (p<.05, t-test). Densities of the core sections from

the "middle position" on the tree did not differ from each other or from the inner

section of the core above the borehole. So, the wood above boreholes had some


resin deposition due to the tapping treatment, but this effect did not extend laterally

or centripetally to the inner section of the core.

Table 6.3. Tree increment core densities, Gainesville FL, 1994
Avg. Density (gm/cc)
Core Core
Position Section Fresh Dry (48 h)
Above Inner 0.927 0.6438
Outer 1.061 0.832b

All 0.772
Between Inner 0.928 0.6960
sides Outer 0.933 0.659"

All 0.674

n = 18 trees

Analysis of monoterpenes in increment core wood samples for 3 trees are

summarized in Table 6.4. Total monoterpene concentrations on a whole-tissue basis

averaged 0.058 mg per g dry weight. These results indicate a very low level of

monoterpenes compared to other published figures (eg. Lewinshohn et al. 1991),

and suggest that the chemical defensive status of the tree was not in a strongly

activated induced response state.

Table 6.4. Monoterpene concentrations in woody tissue of increment core samples
from 3 borehole-tapped trees, 1994.
Monoterpene Concentration
(mg/g d.w.)
alpha pinene 0.034
camphene 0.001
beta pinene 0.016
myrcene 0.001
limonene 0.001
beta phellandrene 0.006
total identified 0.058

Physico-Chemical Properties of Oleoresin

Resin from borehole tapping was naturally found to be very clean and free of

gross contaminants, with less than 1 percent losses (Table 6.5). It was also

extremely clear (X grade), and ranged from a light amber color to nearly colorless.

The turpentine fraction of borehole samples (21.8%) was somewhat higher than for

regular crude oleoresin (15%), which can probably be accounted for by the capture

of volatiles that are normally lost with the open-face production system (Wyman,

1932). Virgin xylem oleoresin from untapped slash pines has been widely reported

to contain 20 to 30 percent monoterpenes, so there was no evidence of heightened

monoterpene levels in borehole-tapped trees. There was no significant difference in

the turpentine fraction among resin sample groups from trees receiving different

levels of CEPA and H2SO4 treatments, as was found for CEPA treatments in

conventional resin production (Kossuth and McReynolds, 1987). High levels of

monoterpenes facilitate resin flow by lowering viscosity (Runckel and Knapp,

1946), but are not a sufficient condition for borehole resin production, since

samples of borehole-produced resin from the low-yielding Maritime pine (P. pinaster)

in France contained very high levels of turpentine (27 to 35%).

Table 6.5. Gross composition of borehole-produced oleoresin, slash pine.
Fraction Percentage
Rosin (diterpenes) 77.2
Turpentine (monoterpenes) 21.8
Other (loss) 0.9

An acetone crystallization test showed that borehole-produced rosin from

slash pine and Pinus oocarpa were free of crystallization, as is the regular rosin


from these species. Tests of resin from other species (P. palustrus, P. pinaster, P.

caribea) showed rapid crystallization. Since slash pine and P. oocarpa were the only

two species which produced high borehole yields, the inherent tendency of resin

acids to crystallize is probably in part responsible for species differences in borehole

resin yields.

Analysis of the resin acid composition of borehole-produced resin by liquid-

gas chromatography showed a higher percentage of pimaric, levopimaric and

palustric, isopimaric, and dehydroabietic resin acids compared to regular WW

American rosin (Figure 6.3). The bottle-collected rosin had a lower percentage of

abietic and other resin acids than regular WW rosin. It was reported by industrial

users that borehole-produced rosin was highly reactive, which is a valuable property

for manufacturing modified resins, since less material is needed as a reactant (Jim

Feltham, Akzo Coatings, Baxley, GA).

Pimaric 6

S Sandaracopimaric

0D Isopimaric

Levopim. & Palustric

U Dehydroabietic

C Abietic

Neo Abietic
All Other 2%

Borehole Rosin
Regu I ar Ros in




0% 5% 10% 15% 20% 25% 30%
Compos ition

Figure 6,3. Resin acid composition of borehole-produced rosin vs. conventionally
produced American rosin (WW grade).




Mechanization of borehole tapping operations was pursued during 1994 to

implement the findings from experimental analysis of the borehole tapping system,

for successful commercialization of the technology.

Need for Mechanization of Borehole Tapping

The concept of a mechanized borehole tapping system was motivated by

results of field trials with non-mechanized borehole tapping operations conducted in

1993. Time and motion studies of borehole treatment and container installation

using a chainsaw-powered drill attachment and 2-liter PET collection bottle, showed

that this system had rather low productivity. Production rates averaged 30 to 35

trees per man-hour, depending upon the type of equipment used and the

organization of labor in two-man or three-man crews. Operating cycle times

measured in field trials averaged 94 seconds per tree for the 3-man crew to drill 3

holes and install bottles (Table 7.1). Unit operation times for drilling, spraying,

installing bottles and moving to the next tree represented 31, 14, 48, and 6 percent

of total cycle time, respectively. The imbalance in operating times is a source of

inefficiency in this system when organized as a 3-man crew: the sprayer operator

was underutilized while the bottle installer was overutilized, and his speed was

limiting to the entire crew. The two-man crew suffered from fatigue for one person

to perform both drilling and spraying. Sustained work on a full day basis is


probably not possible for any of the crew-equipment combinations observed in this

operation. These results showed that both the drilling and bottle installation unit

operations were relatively slow, and have a large potential for increased


Table 7.1. Unit operation times for non-mechanized borehole installation by 3-man
crew, field trials at Waycross GA, July 1993.
Unit Operation Average Time Percentage of
Per Tree (sec) Total Cycle Time
Drill 3 holes with chainsaw powerhead 29.4 31%
and drill attachment
Spray chemical with 3 gallon sprayer 13.2 14%
Install 3, 2-liter PET bottles 45.0 48%
Move to next tree (1 man) 6.0 6%
Total cycle time 93.6 100%
Total man-time 105.6

Mechanized System Design Concepts

Development of equipment for improving productivity of the drilling

operation in borehole tapping logically began with the drilling tool itself and

considerations of hole size and hole quality. The fundamental objective of borehole

tapping is to sever the resin ducts in a cross-sectional area of the tree's sapwood,

and provide a pathway for their drainage. Longtime experience in gum resin

production by conventional open-face bark-chipping methods had demonstrated that

maintaining sharp cutting tools was important for realizing good yields (Clements,

1974). In order to obtain good resin yields, boreholes must be drilled with a clean

cutting action to avoid tearing the wood fibers. A USDA-Forest Service study

which evaluated different cutting tool designs for drilling in southern pine wood

showed that the best holes were obtained with a machine-type double spur, double


twist drill bit (Koch, 1972). This type of drill has cutting edges (spurs) along the

outer radius of the bit which cut in a plane tangential to the wall of the hole,

thereby severing wood fibers and resin ducts at a favorable angle of attack. The

drill bit selected for use in borehole tapping (Irwin 45316) is a machine spur auger

bit that features a 15.2 cm double twist with high pitch to facilitate chip removal, a

heavy duty shank (1.27 cm dia), and a self-feeding screw point which controls the

feed rate and minimizes the thrust force required to advance the drill.

Borehole tapping experiments showed that producing good yields requires

sectioning a sufficiently large basal area of the tree to achieve a near-optimal

tapping intensity. Large diameter boreholes (3.18 cm) and deep boreholes (> 15.2

cm) did not produce greater yields proportionate to their increased area, because of

the diminution in yields per unit area as a function of tapping extent. This

suggested that a strategy of drilling multiple relatively small (2.54 cm dia.)

boreholes was required for a mechanized system. Drilling larger boreholes to attain

the needed hole area was also ruled-out on the grounds of excessive power

required, which would have increased the weight and expense of the drilling

machine, and increased height of holes in the tree, potentially damaging its value

for wood products.

Drilling multiple parallel holes simultaneously by means of a multiple-spindle

drill head was the approach adopted for a mechanized tapping system. Multi-spindle

drill heads have been widely used in the wood and metal fabrication industries for

high production drilling in a variety of patterns, at either fixed or adjustable centers.

This approach was preferred to the alternative of multiple independent drilling units,

due to lower costs and technological complexity.

Drilling holes individually at a significantly faster rate was ruled out as an

option for increasing productivity because of compromised hole quality. The USFS


study (Koch, 1972) showed that better quality holes were obtained when the chip

cutting thickness (the drill "bite") was kept small (0.0254 to 0.0508 cm). This

implies a bounding relationship between the drill feed rate and drill rotational speed

of approximately 10.2 cm per minute per 100 rpm (for a two edged cutting bit). It

was observed experimentally that very high drilling speeds (> 3000 rpm) can cause

excessive heating of the drill bit and "burning" of the hole.

Power required for drilling is a linear function of drill speed and torque, as

given in equation 8, where P is power (kw), n is spindle speed (rpm), and T is

torque (cm-kg).

P=1.587x1 OxnT (8)

Torque for drilling (cm-kg) is related to drill feed rate (f, cm/min), spindle

speed (n, rpm), the number of cutting lips on the drill tool (N =2), and a constant

(C) that is specific to the drilled material, as shown in equation 9.

T=Cx (9)

Torque and thrust forces reported by Koch (1972) were used to calculate power

required for drilling 2.54 cm diameter boreholes with a spur machine-type bit (2

cutting lips), radially in green, high-density, southern yellow pine, for a range of

drilling speeds (Table 7.2). The estimated power required for drilling ranged from

0.24 to .92 kw for drilling speeds ranging from 0.84 to 5.08 cm per second. So, a

conservative design power for the drilling system is 1.12 kw per drill spindle, or 3.4

kw for a 3 drill system, to allow for losses in power transmission. The power

required for thrust is relatively small, and can be ignored.

Table 7.2. Torque, thrust and power required for drilling 2.54 cm diameter holes in
pine wood, at different drilling speeds.
Spindle Chip Feed Torque Thrust Power
Speed Thickness Rate (cm-kg) (kg) Required
(rpm) (cm) (cm/sec) (kw)
1000 .025 0.84 17.4 40 0.24
1000 .076 2.54 33.6 60 0.45
2000 .025 1.70 17.4 40 0.48
2000 .076 5.08 33.6 60 0.92

Mechanized Drilling System Construction

The multi-spindle drill head chosen for the mechanized drilling system (RMT-

Commander 600, Melrose Park, IL) features three adjustable spindle assemblies

which produces a triangular pattern of boreholes with overall widths of 9.5 to 15.2

cm between outer drill centers, and vertical offset of 4.8 to 7.9 cm between the

center and outer holes, as shown in Figure 7.1.

The vertically offset pattern was I 12 1 cm I
9 5 cm
"-:: ------9.5 cm--O--

desirable to reduce interference 7 0 cm
---- ---- ---------- -
between clustered holes, and 5
-2. 54 cm
was shown to increase yields in 7 3 cm 4 8 cm

tapping experiments

(Gainesville, 1994). ----4 8 cm--.

The drill head was Figure 7,1. Hole pattern produced by multi-spindle
drill head.
attached to a drill press

(Hypneumat SP-312, 30.5 cm stroke, Franklin, WI), that is driven from a double V-

belt sheave (12.7 cm dia, type A) on a shaft that runs within the quill feed

mechanism. A custom-fabricated steel frame supports the spindle drive motor and

precision guide rods for the drill head.


The drilling system was powered hydraulically for both its functions of drill

spindle power and drill thrust action. The open-center hydraulic system is provided

with independent pressure and flow control for the two circuits through a flow

divider (Prince RD-1975-16) and dual directional control spool valves (Husco 5001)

with hi and low pressure-relief cartridges. The hydraulic motor (Sunstrand

SNM2/25CI06AHH) delivers 152 cm-kg of torque at 1000 rpm when supplied with

flow of 38 liters/minute at 14900 kg/cm2. Shaft power is transmitted from the

hydraulic motor to the Hypneumat unit by a V-belt drive with double type-A

sheaves in a 4/5 reduction ratio. The Hypneumat drill press provides a thrust force

of 544 kg at 2.54 cm/sec when supplied with flow of 3.8 liters/min at 2980

kg/cm2. A hydraulic gear pump (Sunstrand SNP2/14SCI06) delivers 45 liters/minute

at 3300 rpm.

The complete prototype tapping machine as built is shown in Figure 7.2. The

drilling system is carried on a two wheel, walk-behind tractor (Gravely Pro model).

The Gravely tractor is expected to have a working life of 4000 hours, with proper

maintenance and replacement of the engine (Kohler, 6 kw, cast iron) at midlife.

Extra large tires (56 cm dia x 25 cm) were provided for the tractor to enable good

performance in rough woods conditions. Forward and reverse motion of the tractor

is controlled by a single lever mounted on the handlebars that actuates a cone-type

clutch. The tractor is equipped with a rotary mower (76 cm dia) that functions to

clear a path for the operator and trim vegetation near the base of trees. This heavy-

duty mower is gear-driven through a front PTO from the tractor's transmission. The

tractor also features drum brakes in each wheel hub, which allow brake-steering of

the tractor with a tiller handle, and stabilization of the tractor during drilling with a

parking brake.









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0 0


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The drilling machine was mounted on the front of the tractor to allow a

direct approach to the tree for drilling. A V-shaped guide fashioned from 1.6 cm

steel rod serves to position the drilling head at the center of the tree. At the rear of

the tractor, the hydraulic pump, reservoir and control valves were mounted on a

bracket attached to the tractor's modified drawbar, to counterbalance the added

weight of the drilling machine. The pump is driven through a flexible coupling

(Woods 5J) attached to a driveshaft on the engine flywheel. A 38 liter hydraulic

fluid reservoir was provided for radiative cooling. Hydraulic control valves were

positioned on a mast within easy reach of the operator.

The entire machine system was designed to support a one-pass operation for

complete borehole installation by a single operator. Liquid stimulant is applied to

boreholes with a precision spray gun (Spraying Systems MeterJet) that delivers a

dose of 1 to 16 ml per shot at 596 kg/cm2. Spray solution is fed from a 11.4 liter

garden type pressurized sprayer tank carried in a bracket on the front of the

machine. A large wire basket was mounted on rails atop the tractor's hood to carry

a supply of spout-bag collection devices within reach of the operator. An important

safety and ergonomic design feature is that all three functions for the complete

tapping operation--drilling, spraying, and installing spouts-bags--can be

accomplished by the operator from his station behind the machine if the

recommended operating procedure is followed.

Spout-Baa Collection System

The concept for an improved collection apparatus for borehole tapping began

with the observation that installing 2-liter PET bottles was the single largest unit

operation time, representing nearly half of total time per tree (Table 7.1). In

addition, the extremely bulky bottles were difficult to transport in the field. A more

compact and easily handled container system was clearly needed.

In 1994, work began with an industry cooperator (Navstoc, Inc., Boca Raton

FL), to develop a spout-bag collection apparatus. Plastic bags had been successfully

used for collection of gum resin produced by conventional bark-streaking

operations. High density polyethylene (HDPE) film bags were proven as strong,

durable and leak resistant containers for both the solid and liquid fractions of fresh

pine resin. These bags can be manufactured at low cost by a continuous process of

extruding a thin film of HDPE material (<0.00254 cm) as a tubular sleeve, then

cutting and contact welding to form any size and shape needed. The size of the bag

can be easily adjusted to accommodate the maximum expected resin yield, resulting

in a highly compact and efficient container system in which the amount of plastic

resin used is typically less than one thousandth the volume of the product that it


In conjunction with the plastic bag container, an injection-molded HDPE

spout was designed to channel resin from boreholes into the collecting bag.

Navstoc Inc. has applied for an international patent on this device. The spout has

an overall length of approximately 12 cm, including a tubular outer section that is

slightly tapered and sized to fit tightly in a 2.54 cm diameter borehole, and an open

lattice-frame inner portion which helps to guide spout insertion and insure adequate

hole depth. The outer portion features a flange that seats the spout in the hole, and

threads for attachment to the bag at openings between the weldments that form

the top of the bag. The spout-bag system was designed to be pre-assembled in the

factory with 3 spouts attached to a single bag, and bundled compactly for ready

use in the field. To install the spout-bag device, the three spouts are simply inserted


into their prepared holes and firmly pushed with the hand or hammered with a small


Tests of the Mechanized Borehole Tapping System

The three-hole hydraulic-powered drilling system was first tested in the shop

with log sections. Timed high-speed videotape recordings were made of 30 drilling

trials to assist in measuring drilling rates and identifying problems through slow-

motion replay. A digital photo-tachometer was used to measure and adjust spindle

speeds through changes in the belt drive sheave ratios. Further fine-tuning was

accomplished through adjustment of hydraulic flow rates with the flow divider valve

setting. Pressure settings for the hydraulic circuits were made with permanent in-

line gauges. Drilling speeds of 1000 to 1200 rpm were found to work best with the

self-feeding auger drill bits.

Cycle times for drilling three 2.54 cm diameter holes to a depth of 15.2 cm

in shop tests averaged 13 seconds, including 2 seconds for advancing the bits to

contact the log, 7 seconds drilling under load to the full depth, and 4 seconds to

retract the drill head. Field tests of the drilling machine on live trees (Gainesville FL,

August 1994 experimental plot), resulted in essentially the same unit operating

times. Tests with various types of drill bits showed that non self-feeding (screw-

pointed) bits required such a large thrust force to advance 3 drills into the wood

stock that it was difficult to adequately stabilize the tractor.

The complete borehole tapping machine and spout-bag system was field-

tested at a plantation site near Waycross GA (Waycross State Forest) on three

occasions in July and November 1994 and February 1995. Continuous timed

videotape recordings totaling over 6 hours were made for analysis of the complete

borehole tapping installation cycle. The tapping process was broken-down into 4

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