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 Title Page
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 Introduction
 Relation between soil properties...
 Relation between site quality and...
 Results and discussion
 Summary and conclusions
 Literature cited
 Description of field sampling...














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 559
Title: Soil factors related to growth and yield of slash pine plantations
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027189/00001
 Material Information
Title: Soil factors related to growth and yield of slash pine plantations
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 23 p. : ill. ; 23 cm.
Language: English
Creator: Barnes, Robert L
Ralston, Charles W., 1921-
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1955
 Subjects
Subject: Pinus caribaea -- Growth   ( lcsh )
Pinus caribaea -- Soils   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 17.
Statement of Responsibility: by Robert L. Barnes and Charles W. Ralston.
General Note: Cover title.
General Note: "In cooperation with the School of Forestry"--T.p.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00027189
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000926756
oclc - 18277683
notis - AEN7456

Table of Contents
    Title Page
        Page 1
    Table of Contents
        Page 2
    Introduction
        Page 3
    Relation between soil properties and site quality
        Page 4
    Relation between site quality and volume yield
        Page 5
    Results and discussion
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
    Summary and conclusions
        Page 17
    Literature cited
        Page 17
    Description of field sampling procedures
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
Full Text



Bulletin 559


April 1955


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATIONS
WILLARD M. FIFIELD, Director
GAINESVILLE, FLORIDA
In cooperation with the School of Forestry

TECHNICAL BULLETIN


Soil Factors Related to Growth and

Yield of Slash Pine Plantations

BY ROBERT L. BARNES
and CHARLES W'. RALSTON


Fig. 1.-Number of soil-site quality sample plots by counties.


Single copies free to Florida residents upon request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA






















CONTENTS
PAGE


INTRODUCTION -...- ... ... ........- .. ........- --3


M ETHODS OF INVESTIGATION .....4........ ...... ..............--------..- ------- --- 4


RELATION BETWEEN SOIL PROPERTIES AND SITE QUALITY ..........-........ 4


RELATION BETWEEN SITE QUALITY AND VOLUME YIELD -...... --.-..- -.-...-- 5


RESULTS AND DISCUSSION .... ... ...... . -- -.- -----. 6


SUMMARY AND CONCLUSIONS..... ....... -... -- --------- .... 17


LITERATURE CITED .......- ....-- -------- -- --- ..--- ---------------... ............---.. 17


A PPENDIX ...................---------- -.-...... ...-------..----- -- -------- ---- ----- -- .- 18


Description of Field Sampling Procedures .... ...-.-. --.-------.---------..-- 18


Statistical Analysis ...-.... -- --.-- 19









Soil Factors Related to Growth and

Yield of Slash Pine Plantations
ROBERT L. BARNES 1 and CHARLES W. RALSTON 2

INTRODUCTION
The area of commercial forest land in Florida is 21.4 million
acres, or almost two-thirds of the area of the entire state (5).
However, more than 9.7 million acres, or 45 percent, of the
forest land is seriously understocked or denuded, having less
than 10 percent of the desirable number of trees. Although
some of this understocked area will restock naturally, over 60
percent of the land in the pine and upland hardwood types will
require planting if the full productive capacity of the soil is to
be realized. The latest state survey of forest resources indi-
cates that planting will be required on over seven million acres.
The Florida Forest Service produced 52 million slash pine
seedlings in 1953. With additional planting stock supplied by
industry and other sources, it is estimated that about 72 million
slash pine seedlings were planted, or about 100 thousand acres.
Planting is generally done without an accurate estimate of the
productive capacity of the planting site. Hence, plantations
do not always yield satisfactory returns on the investments.
Although there are seven million acres in Florida that will not
restock naturally in a reasonable length of time, it is certain that
only a part of this area can support commercially profitable plan-
tations of slash pine. Planting should be concentrated on the
more productive sites if the program of restocking is to be of
maximum effectiveness.
In forestry the quality of a given site for producing timber
crops is commonly expressed in terms of the average height of
the dominant trees produced on the area in a given period of
time. This conventional site index technique is usually not
applicable in the case of land in need of planting, because such
land does not ordinarily support an adequate stand of trees for
direct measurement. In Florida slash pine is being planted on
sites which have never supported natural stands of this species.
It is common practice, for example, to plant slash pine on cut-
Instructor in Forestry and Forest Research, School of Forestry, Uni-
versity of Florida.
Assistant Professor of Forest Soils, Duke University, formerly As-
sistant Professor of Silviculture. School of Forestry, University of Florida.






Florida Agricultural Experiment Stations


over longleaf pine land where, even if the site index for long-
leaf were known, an accurate estimate of the site index of the
same land for slash pine could not be made.
The present study was undertaken to provide a method of
rating land for producing planted slash pine irrespective of
present forest cover or land use. Other investigators in the
Southeast have shown that it is possible to correlate certain
features of the soil with the growth of forest trees (1, 3, 4, 6).
This publication presents results of such a study conducted in
slash pine plantations in Florida. The results provide a method
of estimating the future growth and yield of planted slash
pine based on easily recognized soil properties, making it possi-
ble to examine sites in advance of planting and select those
which should yield the most future returns.

METHODS OF INVESTIGATION
The study was carried out in two phases: (1) the establish-
ment of relationships between soil properties and the height
growth of slash pine plantations, thus providing a method of
estimating site quality; and (2) the establishment of relation-
ships between cordwood yields and site quality, age and spac-
ing of plantations.

RELATION BETWEEN SOIL PROPERTIES AND
SITE QUALITY

Field Procedure.-The field work consisted essentially of the
location of suitable plantations, collection of age and height data
to describe the stands, and observation and sampling of the
soil profiles. Adequate geographic coverage of the state was
provided by sampling a total of 269 plantations in 49 counties
(Fig. 1). The distribution of sample plots by height and
age classes is shown in Table 1.
Laboratory Analysis of Soils.-The only soil analysis per-
formed was a mechanical analysis of the heaviest horizon in
each soil profile sampled. The rapid hydrometer method devel-
oped by Bouyoucos (2) was used. One figure representing the
total oven-dry percentage content of silt plus clay was used as
an indication of the moisture-holding capacity of the horizon.
Statistical Analysis.-The data were analyzed by conventional
multiple regression techniques. Average height of the domi-







Soil Factors Related to Growith and Yield of Slash Pine 5

nant trees was considered as the dependent variable, and age
of the stand and various soil factors were tested as inde-
pendent variables. A more thorough presentation of the results
is given in the discussion section, and details of statistical
analyses are given in the appendix.

TABLE 1.-DISTRIBUTION OF SOIL-SITE QUALITY SAMPLE PLOTS BY HEIGHT
AND AGE CLASSES.

Height of Dominant Stand in Feet
Age 11-20 21-30 31-40 41-50 51-60 ;1-70 71-80 Total
Number of Plots

9 2 1 3
10 1 8 5 14
11 6 10 16
12 (6 15 4 25
13 3 17 1; 36
14 3 8 27 38
15 2 2 :2 3 29
16 4 14 1 21
17 1 7 8 16
18 2 2 10 3 17
19 2 8 1 11
20 1 1 3 4 3 12
21 1 3 3 7
22 1 5 6 12
23 1 5 2 8
24 1 1 1 3
25 1 1

Total 3 32 66 86 61 19 2 269


RELATION BETWEEN SITE QUALITY AND
VOLUME YIELD

A second series of 101 sample plots was established for cor-
relating cordwood yields with age, site quality and spacing. The
data were analyzed by multiple regression techniques, as was
the case with the data on height growth, with the difference
that soil factors were not tested as independent variables. In-
stead, a set of site index curves was constructed from the height
and age data in the soil study. These curves were used to
assign a site quality value, based on height and age as measured
in the field, to each volume plot. This site quality value was
based on height of the dominant stand at 25 years, and should
not be confused with the conventional 50-year base which is
used with natural stands in the Southeast.







Florida Agricultural Experiment Stations


RESULTS AND DISCUSSION

The soil factors found to be related significantly to height
growth of slash pine plantations were:
1. Depth to a recognizably fine-textured horizon.
2. Silt plus clay content of the heaviest horizon in the soil
profile.
3. Depth to a mottled horizon.
The influence of these factors on growth may be interpreted
largely through their effects on conditions of soil moisture and
aeration in that portion of the profile which is penetrated by
tree roots. A certain minimum amount of water is necessary if
trees are to survive and grow satisfactorily, but an excess of
water can reduce growth.








i o 0o 20 70 40 50 60 70 80 90 100
5 40 -4 -


50
1-2


5 0 10 20 30 40 50 60 70 80 90 100
DEPTH TO A FINE-TEXTURED HORIZON (INCHES)
Fig. 2.-Site quality for slash pine plantations as influenced by depth to
a fine-textured horizon (depth to mottling and silt plus clay content fixed at
mean values).

The sources of water available to tree roots are: (1) water
entering the soil as precipitation, and (2) water supplied from
the ground water table, both by direct contact with roots and
by upward capillary movement into the root zone. The three
soil variables listed above affect the growth of planted slash pine
by influencing the availability of water from these sources.
A fine-textured horizon in the soil is capable of retaining a
more favorable proportion of water against gravitational drain-
age than a coarse-textured, sandy horizon. (In general, tree
growth improves directly with the nearness to the surface of






Soil Factors Related to Growth and Yield of Slash Pine 7

the fine-textured layer because moisture is more readily avail-
able to the roots. An important exception occurs, only rarely
in Florida, in those soils with topsoil less than 10 inches thick.
Growth is reduced (Fig. 2) since under these conditions the
feeding roots of slash pine are almost entirely confined to the
surface soil, and can draw on only a limited volume of soil. The
deep sand ridge soils support poor growth, due to the fact that
no fine-textured horizon occurs within the depth attained by
tree roots.
The amount of water retained is closely correlated with the
silt and clay content of the soil. This explains the positive
correlation of growth with the percentage content of these fine
materials in the profile. The effect of silt plus clay content is
more pronounced in the sandier soils; apparently a content of
8 to 10 percent silt plus clay is adequate for growth of slash
pine (Fig. 3).


^64~-J-t-------------------------------
064










63 ---

59
0 5 10 15 20 25 30 35 40 45 50
SILT PLUS CLAY CONTENT (PERCENT)
Fig. 3.-Site quality for slash pine plantations as influenced by silt plus clay
content of the heaviest soil horizon (depth to a fine-textured horizon and
depth to mottling fixed at mean values).

In the more poorly-drained soils the depth of the ground water
table exerts an important effect on growth. This effect may be
detrimental or beneficial, depending on the location of the water
table in relation to the soil surface. Extremely wet situations
support poor growth due to deficient soil aeration. However,
the study indicates that if the water table is between 20 and
80 inches below the surface, aeration is not seriously reduced
and the water table apparently supplies beneficial moisture to
the upper soil horizons through capillary action. If the water






Florida Agricultural Experiment Stations


table is extremely deep (more than 80 inches), it does not serve
as a water supply for roots; consequently, growth is somewhat
poorer than if the water table is within the 20-to-80-inch depth.
In this investigation it was not possible to measure the depth
to the water table directly, because it varies throughout the
year, depending on the amount and distribution of precipitation.
It was found, however, that the depth to a mottled horizon in
the profile was related to growth of slash pine in a manner
which conforms closely to the effect of the ground water table
as outlined above. For purposes of statistical analyses, depth
to a hardpan layer, when such a horizon occurred, was consid-
ered as the depth to mottling. It is recognized that the depth
to mottling, or to a hardpan layer, mc.y not represent the depth
to the ground water table in all soils. LA mottled condition, how-
ever, usually indicates a zone of deficient aeration as well as
does the occurrence of the water table- In any case, depth to a
mottled horizon (including hardpan horizons) may be used in
conjunction with the other soil factors discussed above in the
determination of site quality. The relation between depth to a
mottled horizon and the height growth of planted slash pine is
shown in Figure 4.




470
I-

|e o -- y -- -- ----






I--

0 10 _-- -- -

0
S 10 20 30 40 50 60 70 80 90 100
DEPTH TO MOTTLING ( INCHES )
Fig. 4.-Site quality for slash pine plantations as influenced by depth to
mottling (depth to a fine-textured horizon and silt plus clay content fixed at
mean values).






Soil Factors Related to Groith and Iield of Slash Pin 9

Although the effect of silt plus clay content of the heaviest
horizon is significantly related to height growth, the inclusion
of this variable improves estimates of site quality by only a
few feet. Therefore, silt plus clay content has no practical
importance in field determination of site quality. Also, a labora-
tory analysis probably would be necessary to detect the small
differences in fine-textured materials which are associated with
growth responses in the sandier soils. For these reasons, silt
plus clay content is not included as a factor in making growth
estimates by means of Table 2.
Field estimates of site quality, therefore, can be made on the
basis of measurements of the depth of two easily-recognized soil
horizons, namely: (1) a recognizably fine-textured horizon, and
(2) a mottled horizon. In actual field practice the soil profile
could be examined, probably by means of a soil auger or post-
hole digger, and the depth, in inches, to each of these two
horizons determined. Site quality (height at 25 years) is then
estimated by means of Table 2. The predicted height at other
ages may be obtained from Table 3, based on site quality and
age.
If it is desired to estimate the future yield of a plantation
in cordwood volume it is necessary to consider spacing as a
variable. The actual number of trees per acre is required, rather
than spacing at the time of planting, since survival of the
planted trees must be considered in estimates of future yields.
A significant positive correlation exists between site quality
and survival percentage. In other words, the survival of planted
slash pines will be less on the poorer sites than on the better
sites. There is no relation between original spacing and sur-
vival percentage. Table 4 shows the relationship between
plantation survival and site quality, and also shows some origi-
nal spacing patterns converted into number of trees per acre
for estimates of pulpwood volume. The actual survival of a
given plantation will vary with such factors as protective
measures against fire and hogs, rainfall in the months after
planting, and the care taken in planting. Figure 5 indicates
average survival by site quality classes.
Future yields, in cords, of slash pine planted on a given site
may be estimated as follows:
(1) After an examination of the soil profile, and measure-
ments of the depth to: (a) a recognizably fine-textured horizon,
and (b) a mottled horizon, use Table 2 to obtain site quality.







Florida Agricultural Experiment Stations


(2) Having determined site quality and selected the spacing
at which the trees will be planted, use Table 4 to estimate sur-
vival in trees per acre.

80


70






50



0 40
I-





301 -
a '







30 ------------
20 30 40 50 60 70 80
SITE QUALITY (HEIGHT IN FEET AT 25 YEARS)
Fig. 5.-Plantation survival in relation to site quality.

(3) Having determined survival and site quality, use Table
5 to estimate volume yields for ages from 10 to 25 years. Some
interpolation in this table will probably be necessary. Extra-
polation beyond 25 years is not recommended, since growth in
both height and volume declines rapidly beyond this age.
The following example shows how the volume yield of slash
pine pulpwood from a given area could be estimated by using
Tables 2, 4 and 5.
Assume that a soil examination reveals a mottled, fine-tex-
tured horizon at a depth of 40 inches. Using Table 2, the esti-
mated site quality corresponding to a depth to mottling of 40
inches and a depth to a fine-textured horizon of 40 inches is
found to be 70. If the trees are planted at a spacing of 8 x 8
feet, the expected survival (using Table 4) on land of site qual-
ity 70 is 497 trees per acre. Next, the volume yield per acre,







Soil Factors Related to Growth and Yield of Slash Pine 11

TABLE 2.-SITE QUALITY (HEIGHT AT 25 YEARS) FOR SLASH PINE PLANTA-
TIONS IN FLORIDA AS INFLUENCED BY DEPTH TO MOTTLING AND DEPTH
TO A FINE-TEXTURED HORIZON.


Depth to
Mottling
(Inches I

5
10
20
40
(30
80
100


Depth to a Fine-Textured Horizon (Inches)
5 10 20 40 i 0 80
Height in Feet


Basis: 266 sample plots. Standard error of a single observation= = 11
percent of estimated height.


TABLE 3.-HEIGHT OF DOMINANT STAND BY AGE AND SITE QUALITY CLASSES.


Site Quality (Height at 25 Years)
20 30 40 0 oo60 0 80
Height in Feet


TABLE 4.--StRVIVAL (TREES PER ACRE) BY SITE QUALITY CLASSES AND
SPACING AT TIME OIr' PLANTING.


Original
Spacing
(Fe&et)

(3 x ;
8x5
1 x 10
10x 10
10 x 12
12 x 12
14 x 14
16 x 1;


Survival
Percentage


Site Quality (Height at 25 years)
30 40 i 50 0 70
Survival in Number of Trees per Acre


51.1 6(;0.7 6 .4 70.: 73.0 1 75.1







Florida Agricultural Experiment Stations


at an age of 20 years, for example, is found in Table 5. This
yield is found to be about 40 cords per acre, reading roughly
half-way between the values for 400 and 600 trees per acre in
the site quality 70 column opposite 20 years in the age column.


Fig. 6.-Planted slash pine 23 years old on land of site quality 40. Volume
per acre is seven cords. Dominant trees average 37 feet tall.

The economic significance of being able to estimate site quality
before selecting a planting area may be appreciated by a criti-
cal examination of Table 5. If the cordwood volumes at 20
years of age are multiplied by an approximate stumpage value
of $5.00 per cord, the relative values of some of these sites may
be obtained. For example, assuming a stand of 400 trees per
acre, the values per acre of the various site classes are shown
in Table 6.







Soil Factors Related to Gro'wthl and Yield of Slash Pine 13

TABLE 5.-VOLU, ME (CORL3 PER ACRE) BY AGE, SPACING, AND SITE QUALITY.

Trees Site Quality (Height at 25 Years)
Age per _30 40 5_0 6_ 0 __ 70_ 0
Acre Cords per Acre

200 .... .. 1.2 5.0 7.8
400 ....... 4 2. .3 11.6
10 600 ....8 3.9 8.5 14.5
800 .... ..1.2 4.9 10.0 16.5
1,000 ... 1.5 5." 11.1 17.9

200 .. 1. 5.7 10.2 10.4 24.4
400 .. 1.5 7.8 15.6 24.7 35.3
15 600 ... 1.4 .1 18.1 28.6 40.4
800 ... 1.4 i.8 19.5 30.6 43.1
1,000 1.4 10 2 20.4 32.0 44.8

200 3.2 2 11.4 18.1 20.3 36.1
400 3.0 6.0 15.1 25.7 37.7 51.1
20 600 2.8 5.9 1i.0 28.7 42.1 50.8
800 2.7 6.0 17.4 30.2 44.4 59.8
1,000 2.5 6.0 17.9 31.2 45.8 (1,7

200 5.6 9.6 16.2 24.3 33.9 44.9
400 5.5 9.6 20.6 32.8 46.7 61.7
25 600 5.5 .7 22.2 i 36.0 51.3 67.8
800 5.0 9.8 23.1 37.7 53.7 71.0
1,000 5.7 9.9 23.0 i 38.7 55.1 72.9
Basis: 101 sample plots. Standard error of a single observation -- I 3.9
cords.

A comparison of tree growth on land of site quality 40 as
compared with site quality 75 is shown in Figures 6 and 7.

TABLE 6.-VALUE OF PULPWOOD PRODUCED IN 20 YEARS, ON BASIS OF 400
TREES PER ACRE AND STUMPAGE PRICE OF FIVE DOLLARS A CORD, BY
SITE QUALITY CLASSES.

Site Quality
(Height at 25 Years) 30 40 50 60 70 80

Value of Pulpwood,
per Acre (Dollars) .... 15.00 30.00 75.50 128.50 188.50 255.50


It was not possible to use soil series or type names as data
in a statistical analysis of the type which was used in this study.
Quantitative measurements, such as depth and silt plus clay
content, were necessary to establish mathematical relationships
and tests of significance. For those persons who are familiar
with the conventional soil types as they are mapped in Florida,
the information in Table 7 may be useful. In this table soil
series of similar characteristics are grouped together and de-







Florida Agricultural Experiment Stations


scribed briefly. In using this table, one should remember that
depth to mottling or depth to a fine-textured horizon may vary
within a given soil series. For this reason the site quality esti-
mates in the last column of the table should be considered as
averages only. If a more precise estimate of site quality is
desired, the soil should be examined with an auger and the
depth measurements obtained as accurately as possible.


Fig. 7.-Planted slash pine 23 years old on land of site quality 75. Volume
per acre is 36 cords. Dominant trees average 71 feet tall.





TABLE 7-. GENmER CHARACTERISTICS AND Esn-o xvtix SI[T QUAtLITY (OI SoNE CO-AIlMON FLORIDA SOIL.S.


Soil Grioup or Series

Norfolk--liedl Hay Group1
Norlrolk
IAuston
iOran ebiur.

Ani ite

M:ailllblro-(dreeilville Gr'oupl


I' cev'ille
C(arle,'ie
Magnolia
(;ireenvilhl
Hlihkely

.\A redlndo-Kanapaha Group
Artcdondo
( inesvi ille
Fliort Mealde
Kanalp)ali
Fellowship
Alachlua

Lakeland-llhanton Group
Iakelainld
ilanton
Orlanildo

L;alke\wod-St. lucie Group
LSkewoo.
St. ILuio
Pomello


General Description

Well drained, occturrin' on nearly level to
rollin' relief. Friable andiy clay loam or
sandy, clay subsoils at 14 to 30 inches.



Well drainlled. occurrin oiln nearly level to
tundullLlalin'. relief. Sandy clay or sandy
cla l o 1111 subs ils at t 8 to 1 1 inches..





\\ell to moderately well drained. Sandy
suibsoils predominalte, altllhougL1'h sandy
c(lays are commonly found alt :3() + inches
helo\\ the surface.




Well drained, occurrinii on nearly level to
rolling' relief. Sandy subsoils predomi-
niate. Sandy clay subsoils are occasion-
ally found at 50 + inches.

xctessively to moderately well drained.
Subsoils aire salnds throughout. Soil
moisture is probably inadequate fori sat-
isf'actory growth of' slash pine.


Estimated Site Quality lor
Plaiited Slash P'ine

60 to 70, averaging' about ;5.





50 to 65. Int these soils, the clost'r the
sutlsoil 1t the 1 siace. the poorer is the
growth.





55 to. (i.5, occasionally as hip-h as 70 where
the sanny nlay subsoil is within :30 inches
ol the surface.




50 to (I. Deep Lakeland soils ale site
(lqality 50 or less. The better (Orlapdo
soils are about site quality I0.


Less than 50. No plantings were foundd
on soils of this group.








TABLE 7.-GENERAL CHARACTERISTICS AND ESTIMATED SITE QUALITY
(Continued)


OF SOME COMMON FLORIDA SOILS.


Soil Group or Series

Jonesville-Chiefland Group
Jonesville
Chiefland

Hernando-Archer Group
Hernando
Archer

Rex Soils



Scranton and Ona Soils



Leon-St. Johns Group
Leon
Immokalee
St. Johns

Plummer and Rutlege Soils



Bladen-Bayboro Group
Bladen
Bayboro


General Description

Well drained sands 30 inches or more in
depth overlying finer subsoils which rest
on limestone.

Well drained to moderately well drained.
Sandy clay or sandy clay loam subsoils at
less then 30 inches, resting on limestone.

Moderately well to somewhat poorly
drained on nearly level relief. Mottled
sandy clay to sandy clay loam subsoils
usually at 20 to 40 inches.

Imperfect to poor drainage on nearly level
relief. Subsoils usually sandy; fine-tex-
tured materials may be found below 40
or 50 inches.

Imperfectly to poorly drained, occurring,
on nearly level relief. Black or dark
brown organic hardpans at 14 to 42 in-
ches. Subsoils mostly sands.

Poor or very poor drainage, occurring on
flat or depressed areas. Subsoils are pre-
dominantly sands and are saturated with
water throughout much of the year.

Poor drainage, occurring on nearly flat
relief. Mottled sandy clay loam or sandy
clay subsoils at depths of about 10-30
inches.


Estimated Site Quality for
Planted Slash Pine

50-60, occasionally 65 where fine-textured
subsoil is within 30 inches of surface.


65. May be poorer where limestone is
close to surface (less than 15 inches).


60-70. Best growth is on soils which are
not too poorly drained.


55-70. Poorest growth on poorly drained
sands, best growth on soils with fine-tex-
tured subsoil at about 40 inches.

40-55. Occasionally as high as 60 where
hardpan is underlain by sandy clay. Poor
growth where hardpan is at shallow depths.

50-55. These soils have rarely been planted
to slash pine.


S60-65.
I







Soil Factors Related to Growth and Yield of Slash Pine 17

SUMMARY AND CONCLUSIONS
To study the correlation between the growth of planted slash
pine and soil productivity, sample plots were established in a
total of 269 plantations of slash pine throughout Florida. On
each plot, data were collected to obtain the rate of height growth
of the trees, and the soil profile was described and sampled. An
additional 101 sample plots were measured to obtain data on the
rate of cordwood volume growth as related to site quality and
spacing.
Statistical analysis of the data showed that the height growth
of slash pine plantations in Florida can be estimated from two
easily-measured properties of the soil profile:
1. Depth to a fine-textured horizon.
2. Depth to a mottled horizon.
These two variables accounted for 89 percent of the total varia-
tion in height at a given age, and thus provide a convenient
method of estimating the site quality of land for planted slash
pine.
Additional relationships were developed which show how esti-
mates of site quality can be used to predict future yields of cord-
wood for various ages and spacings.
Results of this study should be of value to all persons inter-
ested in establishing plantations of slash pine in Florida. A
relatively simple examination of the soil on a proposed planting
site will provide much valuable information on the growth and
yield to be expected from planted slash pine in future years.

LITERATURE CITED
1. BARNES, R. L., and C. W. RALSTON. Soil factors influencing the growth
of slash pine plantations in northeast Florida. University of Flor-
ida School of Forestry, Research Report No. 1. 11 pp. 1952.
2. BouYoucos, G. J. Directions for making mechanical analysis of soils
by the hydrometer method. Soil Sci. 42: 225-229. 1936.
3. DICKINSON, J. E. Height growth of planted slash pine (Pin)s elliottii
Englm.) as influenced by some physical properties of the soil. Thesis
(M.S. in Forestry). University of Florida. 36 pp. 1950.
4. GOGGANS, J. F. Slash and loblolly pine plantations in Alabama's Pied-
mont Region. Agri. Expt. Sta. of the Alabama Polytechnic Institute.
Circ. 99. 22 pp. 1951.
5. McCoRMACK, J. F. Forest statistics for Florida. Asheville, N. C.,
Southeastern Forest Expt. Sta. (Forest Survey Release No. 36)
73 pp. 1950.
6. RALSTON, C. W. Some factors related to the growth of longleaf pine in
the Atlantic Coastal Plain. Jour. Forestry 19: 408-412. 1951.







Soil Factors Related to Growth and Yield of Slash Pine 17

SUMMARY AND CONCLUSIONS
To study the correlation between the growth of planted slash
pine and soil productivity, sample plots were established in a
total of 269 plantations of slash pine throughout Florida. On
each plot, data were collected to obtain the rate of height growth
of the trees, and the soil profile was described and sampled. An
additional 101 sample plots were measured to obtain data on the
rate of cordwood volume growth as related to site quality and
spacing.
Statistical analysis of the data showed that the height growth
of slash pine plantations in Florida can be estimated from two
easily-measured properties of the soil profile:
1. Depth to a fine-textured horizon.
2. Depth to a mottled horizon.
These two variables accounted for 89 percent of the total varia-
tion in height at a given age, and thus provide a convenient
method of estimating the site quality of land for planted slash
pine.
Additional relationships were developed which show how esti-
mates of site quality can be used to predict future yields of cord-
wood for various ages and spacings.
Results of this study should be of value to all persons inter-
ested in establishing plantations of slash pine in Florida. A
relatively simple examination of the soil on a proposed planting
site will provide much valuable information on the growth and
yield to be expected from planted slash pine in future years.

LITERATURE CITED
1. BARNES, R. L., and C. W. RALSTON. Soil factors influencing the growth
of slash pine plantations in northeast Florida. University of Flor-
ida School of Forestry, Research Report No. 1. 11 pp. 1952.
2. BouYoucos, G. J. Directions for making mechanical analysis of soils
by the hydrometer method. Soil Sci. 42: 225-229. 1936.
3. DICKINSON, J. E. Height growth of planted slash pine (Pin)s elliottii
Englm.) as influenced by some physical properties of the soil. Thesis
(M.S. in Forestry). University of Florida. 36 pp. 1950.
4. GOGGANS, J. F. Slash and loblolly pine plantations in Alabama's Pied-
mont Region. Agri. Expt. Sta. of the Alabama Polytechnic Institute.
Circ. 99. 22 pp. 1951.
5. McCoRMACK, J. F. Forest statistics for Florida. Asheville, N. C.,
Southeastern Forest Expt. Sta. (Forest Survey Release No. 36)
73 pp. 1950.
6. RALSTON, C. W. Some factors related to the growth of longleaf pine in
the Atlantic Coastal Plain. Jour. Forestry 19: 408-412. 1951.






Florida, Agricultural Experiment Stations


APPENDIX

DESCRIPTION OF FIELD SAMPLING
PROCEDURES

SOIL-SITE QUALITY STUDY
The age of plantations sampled ranged from nine to 25 years.
Younger plantations were not sampled, since it was felt that the
development of the root systems of slash pines under nine years
of age was too limited to reflect responses of growth to the full
range of soil factors in a particular locality.
In each plantation a one-tenth acre square plot was estab-
lished where conditions of survival, stocking and soil were rela-
tively uniform. Data were collected for each plot as follows:
Stand data:
1. Age of the plantation-determined from increment borings
of six trees of the dominant stand one foot above the ground.
One year was added to the age thus obtained to allow for the
year in which the seedling was in the nursery.
2. Height-determined by measurements of total height, to
the nearest foot, of the six trees on which determinations of
age were made, and also of four trees in the intermediate crown
class.
3. Diameter-diameter at breast height, to the nearest tenth
inch, of the 10 trees measured for total height. Diameter
measurements were also made on all trees in the third row from
the initially established corner of the plot.
4. Radial growth-determined by measuring the annual
rings, in the three most recent three-year intervals, of the in-
crement borings made to determine age.
5. Original spacing.
6. Total number of trees present when sampled.
7. Percentage of dominant trees.
8. Percentage of survival.
9. Remarks (burning, grazing, number of trees thinned, etc.).
Soil data:
1. A complete description of the soil profile, to a maximum
depth of 100 inches; including a description of the texture, color,
internal drainage and plasticity of all horizons. This informa-
tion was obtained by digging two post holes at a distance of
eight paces, toward the plot center, from two diagonally op-
posite corners of the plot.






Soil Factors Related to Growth and Yield of Slash Pine 19

2. A composite soil sample for each horizon was collected
from the two post holes for later laboratory analysis.
3. Supplemental borings were made with a soil auger to de-
termine the average depth of the At horizon, average depth to
mottling and average depth to a recognizably fine-textured
horizon, if such horizons were found within 40 inches of the

4. Surface drainage.
5. Percentage of slope.

SITE QUALITY-SPACING-VOLUME STUDY
Due to the wide range in spacing encountered in the planta-
tions, it was necessary to vary the size of the sample plots used
to collect data for volume computations. For example, the
widest spacing found was 20 x 20 feet, or about 109 trees per
acre. In contrast, a 6 x 6 spacing represents 1,210 trees per
acre. Obviously a one-tenth acre sample plot would not be
satisfactory in plantations established at the wider spacings.
For this reason, plot size was varied so as to include at least
40 trees on each plot. A minimum plot size of one-tenth acre
was used; the maximum plot size required was almost one-half
acre in area.
The stand data which were collected on the 101 plots used
in this part of the study were essentially the same as the data
listed under the soil study. Additional data included:
1. A complete tally, by one-inch diameter classes, of all trees
on the sample plot.
2. Bark thickness, to the nearest .05 inch, of the 10 trees
which were measured for total height.
Soil data were not collected.

STATISTICAL ANALYSIS
SOIL-SITE QUALITY STUDY
The typical sigmoid curve for height growth as related to
age was transformed to a linear function, as proposed by Schu-
macher 2 and as shown in the equation:

For details of computational procedures see: Schumacher, F. X.. and
R. A. Chapman. Sampling methods in forestry and range management.
Duke Univ. School of Forestry Bull. 7. 222 pp. 1948.
SSchumacher, F. X. A new growth curve and its application to timber
yield studies. Jour. Forestry 37: 819-820. 1939.






Florida Agricultural Experiment Stations


1
Logarithm of height = b + bi -
Age

where b,, and b, are constants which are derived from a particu-
lar set of data by means of regression analysis. The effect of
soil factors on height growth was determined through their
addition as independent variables to this basic equation.
The complete list of variables used in the analysis was as
follows:

y = logarithm of average height of the dominant trees
in the plantation (the dependent variable).
x, = reciprocal of age of the plantation.
x2 = depth to mottling.
x3 == depth to a fine-textured horizon.
x, = reciprocal of depth to mottling (hence 1/x.).
x. = reciprocal of depth to a fine-textured horizon
(hence 1/x,).
x,; = reciprocal of the silt plus clay content of the heavi-
est horizon in the profile.
x7 = interaction of x, and x,.
x, = interaction of x, and x,.
x, = interaction of x, and x,.
x,, = interaction of x, and x.,.
xj = interaction of x, and x,;.
X12= (X,)2.

The initial analysis showed that the independent variables
XI, x-, X:, x4, x., and x,; were significantly related to height growth.
By means of the regression equation based on these six inde-
pendent variables, the estimated height of each of the 269 sam-
ple plots was calculated by substitution of observed plot data in
the equation. The differences between observed heights, as ac-
tually measured in the field, and estimated heights, as calculated
from this first regression equation, were computed for each plot.
For three plots, the deviation between observed and estimated
values was more than four times the standard error of estimate.
Consequently, the data from these plots were deleted and the
final analysis was completed on 266 plots. The growth of each
of the three discarded plots was definitely inferior to the aver-
age of other plots growing on similar sites, -ii.L'-tlir that







Soil Factors Related to Growth and Yield of Slash Pine 21

some unmeasured factor had probably resulted in such ex-
tremely poor growth.
The final regression equation, which was used in computing
the site quality values listed in Table 2 of the bulletin, was:

y = 2.3058 5.8369 (xl) .001345 (x,)
.001807 (x,) 2.4939 (x,) 1.1874 (x,)
.05137 (x,;)

Since the coefficient for x,, (reciprocal of silt plus clay content)
is so small, this variable adds very little to the accuracy of
estimates of site quality. The mean value of silt plus clay con-
tent for all 266 plots (about 10 percent) was therefore substi-
tuted for x, in the final equation for the purpose of construction
of Table 2.
The analysis of variance appropriate to the final regression
equation is shown in Appendix Table 1.

APPENDIX TABLE 1.-FINAL ANALYSIS OF VARIANCE, SOIL-SITE QUALITY
STUDY; 266 PLOTS (ALL VARIABLES CODED).

Source D.F. S.S. ?.S.

X, (1/Age) ...................... 1 117,018 117,018
X, (depth to mottling) ... 1 4,819 4,819
Xa (depth to fine-texture) 1 14,999 14,999
X, (1/X ) ................. 1 4,562 4,562
X; (1/X ) ........ ..... .. 1 11,013 11,013
X, ...... 1 6,646 6,646
Residuals ............... 259 33,619 130

TOTAL ............... 265 192,676

*All variables significant at 1 percent level.

SITE OUALITY-SPACING-VOLUME STUDY
The form class volume tables derived by Minor I were used to
calculate tree volumes in rough cords. As a preliminary part of
the study, the form classes of 100 plantation-grown slash pine
trees selected to cover the expected range of height, diameter
and age were measured by using a ladder. The analysis of these
data showed that form class of standing trees could be estimated
satisfactorily from an equation based on total height and diam-

SMinor, C. O. Form class volume tables for use in southern pine pulp-
wood timber estimating. Baton Rouge, La. Agr. Expt. Sta. Bull. 445.
39 pp. 1950.







Florida Agricultural Experiment Stations


eter and bark thickness at breast height.4 For this reason, bark
thickness measurements were included for the 10 sample trees
measured on each of the 101 volume plots.

APPENDIX TABLE 2.-DISTRIBUTION OF VOLUME PLOTS BY AGE
AND VOLUME.

Volume Age
(Cords per 9-11 12-14 15-17 18-20 21-23 24-25 Total
Acre) Number of Plots

0-10 8 14 6 4 2 34
11-20 14 7 5 26
21-30 5 9 3 3 20
31-40 2 5 6 2 15
41-50 2 1 3
51-60 1 1
61-70 2 2

Total 8 33 24 19 13 4 101


The procedure in calculating plot volumes was based on curves
of height over diameter and of bark thickness over diameter
for the 10 sample trees. Curved values for height and bark
thickness were then assigned to each diameter class of the com-
plete plot tally. Form class for each diameter class was also
computed by means of the equation mentioned above. Finally,
the volume in rough cords for the trees of each diameter class
was obtained from the appropriate section of Minor's tables and
multiplied by the number of trees in that class. Cordwood
values were then summed over all diameter classes, and the
total multiplied by the appropriate correction factor, based on
plot area, to convert volumes to values per acre. Trees under
four and one-half inches in diameter were considered as having
no merchantable volume.
The site quality of each plot was determined from a set of
site index curves based on the height growth data obtained
in the soil-site quality study. The regression analysis was then
completed using cordwood volume as the dependent variable,

'The equation used to estimate form class (F.C.) from diameter (D),
total height (H), and bark thickness (B) was:
106.1 892.2 8.3
F.C. = 88.0 --
D H B
Diameter and bark thickness are expressed in inches and total height is
expressed in feet.







Soil Factors Related to Growth and Yield of Slash Pine 23

and various functions of age, site quality and spacing (ex-
pressed as number of trees per acre) as independent variables.
The resulting equation was used to compute values for Table 5
in the bulletin.

APPENDIX TABLE 3.-DISTRIBUTION OF VOLUME PLOTS BY SITE
QUALITY AND VOLUME.

Volume Site Quality (Height at 25 Years)
(Cords per 21-30 31-40 4150 51-60 61-70 71-80 Total
Acre Number of Plots

0-10 1 6 5 13 9 34
11-20 5 19 2 26
21-30 2 8 10 20
31-40 3 8 4 15
41-50 2 1 3
51-60 1 1
61-70 2 2

Total 1 5 23 47 19 101




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