• TABLE OF CONTENTS
HIDE
 Title Page
 Credits
 Introduction
 General discussion of the humus...
 Description of field conditions...
 Typical humus layer of longleaf...
 Maximum depth of forest floor
 Rate of accumulation of forest...
 Chemical composition of the humus...
 Summary
 Literature cited
 Historic note






Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; 302
Title: Field characteristics and partial chemical analyses of the humus layer of longleaf pine forest soils
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027428/00001
 Material Information
Title: Field characteristics and partial chemical analyses of the humus layer of longleaf pine forest soils
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 27 p. : ill. ; 23 cm.
Language: English
Creator: Heyward, Frank
Barnette, R. M
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1936
 Subjects
Subject: Longleaf pine -- Soils   ( lcsh )
Humus   ( lcsh )
Forest soils   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 25-27.
Statement of Responsibility: by Frank Heyward and R.M. Barnette.
General Note: Cover title.
 Record Information
Bibliographic ID: UF00027428
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924380
oclc - 18212701
notis - AEN5000

Table of Contents
    Title Page
        Page 1
    Credits
        Page 2
    Introduction
        Page 3
    General discussion of the humus layer
        Page 4
        Page 5
    Description of field conditions in the longleaf pine region
        Page 6
        Page 7
        Page 8
    Typical humus layer of longleaf pine forests
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Maximum depth of forest floor
        Page 14
        Page 15
    Rate of accumulation of forest floor
        Page 16
        Page 17
        Page 18
    Chemical composition of the humus layer
        Page 19
        Page 20
        Page 21
        Page 22
    Summary
        Page 23
        Page 24
    Literature cited
        Page 25
        Page 26
        Page 27
    Historic note
        Page 28
Full Text




UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA
WILMON NEWELL, Director


FIELD CHARACTERISTICS AND

PARTIAL CHEMICAL ANALYSES OF
THE HUMUS LAYER OF

LONGLEAF PINE FOREST SOILS
By FRANK HEYWARD
Assistant Silviculturist, Southern Forest Experiment Station
U. S. Forest Service
and
R. M. BARNETTE
Chemist, Florida Agricultural Experiment Station


















Fig. 1.-Forest floor under longleaf pine unburned for 15 years. A
12-inch scale is shown in this and following illustrations. U. S. Forest
Service photo.

TECHNICAL BULLETIN

Bulletins will be sent free to Florida residents upon application to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


September, 1936


Bulletin 302








EXECUTIVE STAFF
John J. Tigert, M.A., LL.D., President of
the University
Wilmon Newell, D.Sc., Director
H. Harold Hume, M.S., Asst. Dir., Research
Harold Mowry, M.S.A., Asst. Dir., Adm.
J. Francis Cooper, M.S.A., Editor
Jefferson Thomas, Assistant Editor
Clyde Beale, A.B.J., Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager
K. H. Graham, Business Manager
Rachel McQuarrie, Accountant

MAIN STATION, GAINESVILLE
AGRONOMY
W. E. Stokes, M.S., Agronomist**
W. A. Leukel, Ph.D., Agronomist
G. E. Ritchey, M.S.A., Associate*
Fred H. Hull, Ph.D., Associate
W. A. Carver, Ph.D., Associate
John P. Camp, M.S., Assistant
ANIMAL HUSBANDRY
A. L. Shealy, D.V.M., Animal Husbandman**
R. B. Becker, Ph.D., Dairy Husbandman
L. M. Thurston, Ph.D., Dairy Technician
W. M. Neal, Ph.D., Asso. in An. Nutrition
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Veterinarian
N. R. Mehrhof, M.Agr., Poultry Husbandman
W. W. Henley, B.S.A., Asst. An. Husb.*
W. G. Kirk, Ph.D., Asst. An. Husbandman
R. M. Crown, B.S.A., Asst. An. Husbandman
P. T. Dix Arnold, B.S.A., Assistant Dairy
Husbandman
L. L. Rusoff, M.S., Laboratory Assistant
Jeanette Shaw, M.S., Laboratory Technician

CHEMISTRY AND SOILS
R. W. Ruprecht, Ph.D., Chemist**
R. M. Barnette, Ph.D., Chemist
C. E. Bell, Ph.D., Associate
R. B. French, Ph.D., Associate
H. W. Winsor, B.S.A., Assistant
ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agricultural Economist**
Bruce McKinley, A.B., B.S.A., Associate
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Assistant

ECONOMICS, HOME
Ouida Davis Abbott, Ph.D., Specialist**
C. F. Ahmann, Ph.D., Physiologist
ENTOMOLOGY
J. R. Watson, A.M., Entomologist**
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant

HORTICULTURE
G. H. Blackmon, M.S.A., Horticulturist and
Acting Head of Department
A. L. Stahl, Ph.D., Associate
F. S. Jamison, Ph.D., Truck Horticulturist
R. J. Wilmot, M.S.A., Specialist, Fumigation
Research
R. D. Dickey, B.S.A., Assistant Horticulturist
PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist**
George F. Weber, Ph.D., Plant Pathologist
R. K. Voorhees, M.S., Assistant
Stacy O. Hawkins, M.A., Assistant
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Assistant Botanist
SPECTROGRAPHIC LABORATORY
L. W. Gaddum, Ph.D., Biochemist
L. H. Rogers, M.A., Spectroscopic Analyst


BOARD OF CONTROL
Geo. H. Baldwin, Chairman, Jacksonville
Oliver J. Semmes, Pensacola
Harry C. Duncan, Tavares
Thomas W. Bryant, Lakeland
R. P. Terry, Miami
J. T. Diamond, Secretary, Tallahassee


BRANCH STATIONS
NORTH FLORIDA STATION, QUINCY
L. O. Gratz, Ph.D., Plant Pathologist in
Charge
R. R. Kincaid, Ph.D., Asso. Plant Pathologist
J. D. Warner, M.S., Agronomist
Jesse Reeves, Farm Superintendent
CITRUS STATION, LAKE ALFRED
A. F. Camp, Ph.D., Horticulturist in Charge
John H. Jefferies, Superintendent
Michael Peech, Ph.D., Soil Chemist
W. A. Kuntz, A.M., Assoc. Plant Pathologist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Asst. Entomologist
EVERGLADES STATION, BELLE GLADE
A. Daane, Ph.D., Agronomist in Charge
R. N. Lobdell, M.S., Entomologist
F. D. Stevens, B.S., Sugarcane Agronomist
Thomas Bregger, Ph.D., Sugarcane Physiologist
G. R. Townsend, Ph.D., Assistant Plant
Pathologist
J. R. Neller, Ph.D., Biochemist
R. W. Kidder, BS., Assistant Animal
Husbandman*
Ross E. Robertson, B.S., Assistant Chemist
B. S. Clayton, B.S.C.E., Drainage Engineer*
SUB-TROPICAL STATION, HOMESTEAD
H. S. Wolfe, Ph.D., Horticulturist in Charge
W. M. Fifield, M.S., Asst. Horticulturist
Geo. D. Ruehle, Ph.D., Associate Plant
Pathologist
W. CENTRAL FLA. STA., BROOKSVILLE
W. F. Ward, M.S., Asst. An. Husbandman
in charge*

FIELD STATIONS
Leesburg
M. N. Walker, Ph.D., Plant Pathologist in
Charge
W. B. Shippy, Ph.D., Asso. Plant Pathologist
K. W. Loucks, M.S., Asst. Plant Pathologist
J. W. Wilson, Ph.D., Associate Entomologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
Cocoa
A. S. Rhoads, Ph.D., Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Plant Pathologist
Monticello
Asst. Entomologist
Bradenton
Dsvid G. Kelbert, Asst. Plant Pathologist
C. C. Goff, M.S., Assistant Entomologist
Sanford
E. R. Purvis, Ph.D., Assistant Chemist,
Celery Investigations
Lakeland
E. S. Ellison, Ph.D., Meteorologist*
B. H. Moore, A.B., Asst. Meteorologist*
In cooperation with U.S.D.A.
** Head of Department.









FIELD CHARACTERISTICS AND PARTIAL CHEMICAL
ANALYSES OF THE HUMUS LAYER OF
LONGLEAF PINE FOREST SOILS

By FRANK HEYWARD and R. M. BARNETTE1

CONTENTS
Page
Introduction ............... .......... ........ ........ .......................... .......... ........................... 3
General Discussion of the Humus Layer .................. ..................................... ... .................. 4
Description of Field Conditions in the Longleaf Pine Region ............................................ 6
Typical Humus Layer of Longleaf Pine Forests ................................... ............................ 9
Maximum Depth of Forest Floor .............................. .................... ............................. 14
Rate of Accumulation of Forest Floor ......................................... ........... ...... .................... 16
Chemical Composition of the Humus Layer .................................. ............................... 19
Summary ....................................................................... 23
Literature Cited .................... .... .............. ........ ....................... ........ .................... .......... 25

During recent years the importance of an understanding of
the humus layer of forest soils has been widely recognized, both
in this country and abroad. Much attention has been given
the effect of forest on soil and also the effect of soil on forest
(5, 6, 8, 11, 14, 27, 32).2
The humus layer is frequently the origin of important in-
fluences of the soil on forest growth. Powers and Bollen (21)
concluded that the nutrient supplying power of forest soils is
centered in the F and H-layers, especially as to bases and
nitrates. Waksman (29) states, the humus layer gives
to forest soil some of its most important characteristics, and
contributes materially, if not largely, to the development of
the individuality of the soil." Moreover, it has been found
that the silvicultural treatment of the stand may profoundly
alter the characteristics of this horizon (5, 6, 9, 11, 33). Un-
favorable conditions of the humus layer may frequently be
bettered by silvicultural methods, such as change of stand
composition, methods of cutting, and thinning, or by use of
controlled fire, or by draining. Moreover, favorable humus
conditions may be altered to less favorable conditions through
unwise silvicultural practices. Hence, it is logical for the silvi-
culturist to include in his fundamental studies of forest manage-

1The authors acknowledge the assistance of H. W. Jones and N. A.
Murray in performing the chemical analyses reported in this study.
2Italic figures in parentheses refer to "Literature Cited" in the back
of this bulletin.






Florida Agricultural Experiment Station


ment the nature and properties of the humus layer in order
that its true value may be intelligently appraised and therefore
considered in management plans of the forest.

GENERAL DISCUSSION OF THE HUMUS LAYER
The humus layer is the soil horizon or horizons in which
occurs the breakdown of organic matter. It is within the
humus layer that litter breaks down with the resultant forma-
tion of true humus.3 The humus layer is, according to Romell
(22) "the horizon of humus formation, the seat of briskest
activity of the soil life".
As long ago as 1887, P. E. Miiller (19), one of the pioneers
of forest soil science, recognized two definite conditions of
humus in forest soils. These he called "mull" and "mor". Be-
cause of variations within these types, much confusion has
arisen as a result of the use of countless descriptive terms
applied to each. Nevertheless, it seems highly probable, as
shown by Romell's researches in this country and in Europe,
and as pointed out by Waksman (29), that all humus types likely
to be encountered may be classed as some form of mull or mor.
A typical mull humus layer is characterized by an intimate
mixture of organic materials and mineral soil. The resulting
horizon, called the "mull horizon", is well flocculated, loose, and
friable. Only one to two years' accumulation of litter is gen-
erally present, the rapid breakdown of litter and its resultant
incorporation into the mineral soil being one of the distinguish-
ing characteristics of mull. Large earthworms are typically
present in mull; indeed, these soil animals are regarded as being
a potent factor in mull formation, although myriapods (23)
and probably other organisms may also be of importance in
this connection. Mull soils are highly desirable from a fertility
standpoint, particularly with respect to available nitrogen. That
they represent a humus condition highly desirable for forest
growth is a fact of long standing in European silviculture. Al-
though there are many exceptions, mull soils are generally asso-
ciated with hardwood forests. As Heimburger (10) mentions,
a mull may be too fertile for optimum growth of conifers.
The mor humus type differs from mull in having a layer of
organic matter, usually distinctly matted, on top of the mineral

sin this paper the term "humus" denotes the dark colored, partly de-
composed soil organic residues whose constituent parts are no longer macro-
scopically distinguishable.







Humus Layer of Longleaf Pine Forest Soils


soil and sharply delimited from it. This layer consists of sev-
eral to many years' accumulation of organic materials. Three
distinct subdivisions of the forest floor of mor humus types
are now accepted.4 These are (1) the L-layer or litter, the F
or fermentation layer, and the H or humification layer (11).
However, in many mors the H-layer may be very inconspicu-
ous or entirely absent.
Pedologists, not specialists in forest soils, frequently object
to the term "humus layer" being used to designate the F and
H-layers of mor. They contend that the H or humification layer
alone is the layer of true humus. If the humus layer be re-
garded as the combined several horizons of organic detritus in
varying degrees of decay between the litter stage and the stage
of well mineralized material of the H-layer, and the H-layer
alone thought of as true humus, then apparent ambiguity of
terms will be avoided. It is worthy of note that Waksman, in
the latest of his classical publications on humus, refers to
the humus of forest soils as "all the plant and animal residues
brought upon or into the soil and undergoing decomposition"
(29, page 214). This definition clearly includes the F-layer
as part of the humus layer. Visible decomposition to the un-
aided eye is reasonably understood, since, although freshly fallen
litter is generally regarded as not beginning decomposition for
some time, depending on various factors, Griffith, et al. (8)
point out that ash leaves are often attacked by fungi while
yellowing on the tree.
An active soil microfauna may be present in either mull or
mor, but Bornebusch (4) states that a small number of individ-
ually large animals, the most important of which are earth-
worms, characterize mull, whereas a large number of small
animals characterize mor. For detailed discussions of humus
layers the reader is referred to recent papers by Romell (22,
23, 24, 25).

4Unincorporated organic matter overlying mineral soil is sometimes
referred to ap. "cover humus", but is preferably designated as "forest
floor" (16). The forest floor of mor under conditions unfavorable to de-
composition is called raw-humus. Raw-humus may accumulate to depths
of one to two feet or more.
Throughout this paper the term "Ao horizon" to denote unincorporated
organic matter is avoided. Romell, in a personal communication, pointed
out that the Scandinavian conception of "humus layer" and the Russian
classification, employing use of the letters "Ao" and "Ai", do not always
harmonize. The mull horizon is the H-layer of mull humus types, whereas
it would be A, according to the Russian designation.






Florida Agricultural Experiment Station


DESCRIPTION OF FIELD CONDITIONS
IN THE LONGLEAF PINE REGION

The longleaf pine region is a belt from 75 to 200 miles wide,
immediately adjacent to the Atlantic and Gulf Coasts from
North Carolina to Texas. This vast area is one of the most
important forest regions of the United States. The soils are
largely derived from fine sands and fine sandy clays of marine
origin. In texture, they vary from medium sand to silt loam;
but by far the greater percentage of the pine forests grows on
soils ranging in texture from fine sand to sandy loam. These
soils are deficient in lime (pH values range from approximately
4.0 to 5.5) and are also low in nitrogen and organic matter.
Mean annual
rainfall varies
from 40 to 60
inches or more.
Mean summer
temperatures
are between 70
and 90 degrees
and mean win-
t e r tempera-
tures between
40 and 60 de-
grees.
Within the
longleaf p in e
region, during
p as t genera-
tions, it has
been custom-
ary for the
inhabitants to
intentionally
spread fire
through the
woods during
the winter.
Fires may
largely be at-
Fig. 2.-Virgin stand of longleaf pine in the vicinity
tribute to cat- of Nashville, Ga. U. S. Forest Service photo.






Humus Layer of Longleaf Pine Forest Soils


tie owners who burn the woods for the purpose' of improving
the early spring range, and also to naval stores operators. The
latter rake all combustible material from the base of each tree
being worked for gum, and then intentionally burn the forest
in order to safeguard against accidental fires which would cause
great damage to naval stores equipment. Throughout the region
the greater percentage of well drained forest soils supports
stands of longleaf pine (Pinus palustris Mill.). This pine is
recognized as being remarkably resistant to fire. Typically, it
grows in open stands with no high underbrush (Fig. 2). Because
of these characteristics, longleaf pine forests occur even on
lands subjected to annual or biennial fires. Under such condi-
tions, it is obvious that development of a humus layer from
forest detritus would be interrupted in its incipiency. The
only organic material on the soil surface, other than living
plants, would, therefore, consist of from one to possibly three
years' accumulation of pine litter and dead portions of plants,
mainly perennial grasses, comprising the ground cover (Fig. 3).



















Fig. 3.-Ground cover, chiefly perennial grasses, typical of frequently
burned longleaf pine forests. Urania, La. U. S. Forest Service photo.

Under conditions of repeated fires, such as those which have
existed for scores of years in the longleaf pine region, a humus
layer difficult to classify has developed. This humus layer is
characteristic of grassland rather than of forest land. It con-






Florida Agricultural Experiment Station


sists of a compact horizon of mineral soil in which decayed roots,
chiefly those of perennial grasses, constitute the only source of
organic matter. This horizon, called "Ai" by soil surveyors, is
from 2 to 31/ inches thick, varying in color from a light gray,
only slightly darker than the underlying soil, to almost black,
depending on moisture conditions. Litter and F-layers are
absent. No evidence of an active soil fauna is visible. This
humus layer may be considered as a "fire climax", since it was
brought into existence and maintained as a result of recurrent
fires.
During the past 10 years, however, certain social policies
have changed in the region. The public has become forestry
minded, and has, for the first time, assumed a critical attitude
towards forest fires. This is particularly true now that it has
been established as a fact that the highly desirable slash pine
(P. caribaea More.) reproduces only on areas protected from
fire. With increasing interest in forestry, timber lands all over
the South are being afforded protection from fire. It is now
possible to find tracts thousands of acres in extent, which have
been protected from fire for periods ranging from five to 10
years. As would be expected, the abrupt change from repeated
burning to complete protection from fire has caused manifest
changes in the properties of the soil (12, 13).6 Among such
changes, those associated with the humus layer are noteworthy.
These changes are largely due to replacement, following exclu-
sion of fire, of the luxuriant ground cover, typical of frequently
burned areas, by a well developed forest floor (Fig. 4). For
the first time, for generations at least,6 a humus layer typical
of forest conditions and not of grassland is developing in the
longleaf pine region.
Although an understanding of the salient properties of the
humus layer is of value to silviculture in the region, no studies
on this subject have been published. The present bulletin de-
scribes some of the most important characteristics of the humus
layer of pine forest soils in the longleaf pine region protected
from fire for at least 10 years. The data and observations here

5A paper on "Some changes in the soil fauna associated with forest
fires in the longleaf pine region", by Frank Heyward and A. N. Tissot, is
to be published in Ecology 18:1. 1937.
6Numerous historical records show conclusively that forest fires were
of common occurrence during the earliest colonial days and that they
probably had been frequently started by Indians during hunting expedi-
tions prior to arrival of the white man.






Humus Layer of Longleaf Pine Forest Soils


presented are based on a study of 42 areas widely distributed
over the region.




















Fig. 4.-Forest floor under closed stand of longleaf pine following
protection from fire. The ground cover has been completely smothered
out by litter. Note persistence of the grass vegetation in the opening
of the stand in the background. Adrian, Ga. U. S. Forest Service photo.

TYPICAL HUMUS LAYER OF LONGLEAF PINE FORESTS
Owing to the comparatively uniform conditions of site and
timber stands in the longleaf pine type, it seems unlikely that
a large variety of humus layers will develop, even though a
general policy of complete protection from fire be adopted.
Romell and Heiberg (25) described 12 varieties of humus layers,
4 mull and 8 mor forms, for northeastern United States. This
large number may be attributed to a diversified topography and
to forest types typical of mountainous country. However, ex-
amination of soil conditions in the 42 areas forming the basis
of the present study revealed a surprisingly constant type of
humus layer under longleaf, as well as slash pine, on well to
moderately well drained sites. These stands were distributed
from South Carolina to Louisiana. Although all of the areas
selected for study had been protected from fire for at least 10
years, it is almost a certainty that many of these had been
burned over at least once during the life of the present stand.7

7See footnotes 6 and 10.






Florida Agricultural Experiment Station


Some of the characteristic physical and chemical properties of
the typical humus layer under long unburned pine stands follow.
The prevailing humus layer under pine in the longleaf region
possesses characteristics intermediate between those of mull
and mor. It consists of an F-layer and a discontinuous, indis-
tinctly developed H-layer (Figs. 5 and 6). The F-layer gen-
erally rests directly on mineral soil and is sharply delimited
from it, especially on sandy soils (Fig. 7). No definite separa-



















Fig. 5.-Forest floor under longleaf pine unburned for at least 30 years.
Glen Saint Mary, Fla. U. S. Forest Service photo. (Cf. Fig. 6.)

tion of litter from F-layer is possible, since one grades gradually
into the other. However, a fairly constant field characteristic
offers a convenient means of separating what may arbitrarily
be called litter from the F-layer. In general, pine needles in
this region retain their original form for 21/2 to 3 years. Dur-
ing the third or fourth year decomposition and disintegration
processes progress to such an extent that the needles begin to
break up. Because of this condition, it is possible to lift the
litter of the current year and the past two years from the under-
lying F-layer, as shown in Fig. 6. The litter is usually from
%3 to 11/ inches in depth.
The F-layer varies in thickness from 1/2 to 11/ inches. It
consists of partly decomposed or disintegrated organic matter







Humus Layer of Longleaf Pine Forest Soils


Fig. 6.-Detailed view of forest floor shown in Fig. 5, clearly showing
litter and F-layer. Note the small animal tunnels in the underlying mineral
soil. Glen Saint Mary, Fla. U. S. Forest Service photo.


Fig. 7.-Profile of humus layer under longleaf pine. The F-layer rests
directly on mineral soil. The tunnels were probably made by pine mice.
Practically every square foot of this area examined was crossed by at
least one tunnel. Glen Saint Mary, Fla. U. S. Forest Service photo.






Florida Agricultural Experiment Station


whose constituent parts are still macroscopically distinguishable.
This layer is generally loosely arranged. It is penetrated by
numerous feeding roots of pine on which mycorrhiza abound,
iand is interwoven with fungus mycelia. Microscopic examina-
tion revealed that fungal tissue was omnipresent in this layer.
No continuous H-layer is present. In small depressions, not
more than one foot in diameter, a thin H-layer less than 1/8-inch
may be distinguished. Immediately overlying the mineral soil
occurs a thin layer of frass and excrement from the lesser mem-
bers of the soil fauna. The large, shot-like pellets, approximately
1/8 inch in diameter, of millipedes are extremely abundant on
dry sandy soils and may be gathered, in localized spots, by the
tablespoonful. Even where this layer of excrement is very pro-
nounced, there is no indication of a mixing of such material
and mineral soil.



















Fig. 8.-Small animal tunnel, probably made by mice, under forest
floor of longleaf pine forest protected from fire for 14 years. McNeill,
Miss. U. S. Forest Service photo.

The upper portion of the A horizon, the A1, is the location
of intense animal activity. This horizon, sometimes to a depth
of 3 inches, is a labyrinth of small animal burrows (Figs. 7
and 8). Many holes occur, which lead vertically downward to
undetermined depths, or downward for less than one inch where
they connect with horizontal tunnels. On several of the areas
visited this particular type of activity was judged to be the






Humus Layer of Longleaf Pine Forest Soils


most important single factor influencing the physical properties
of the soil.8
The A1 horizon of soils heavier in texture than fine sand was
definitely mull-like in character. Earthworm casts were abun-
dant, and the soil was frequently of fairly good crumb structure
to a depth of 2 inches. Again, however, the transition from
organic matter to mineral soil was too abrupt to be typical of
a good mull.9
Because of the active soil fauna and also the protective layer
constituting the forest floor, the AI horizon of both sandy and
heavier soil types is frequently so porous that it resembles a
sponge in structure. Small portions 4 inches or less in diameter
commonly have a volume weight of less than one.
From the foregoing description it might seem that the A1
horizon of pine forest soils would be high in organic matter.
Such is not the case, however. Heyward and Barnette (13)
presented figures on ignition loss for the AI horizon of eight
pine forest soils distributed from Georgia to Louisiana. In
spite of possible high values due to presence of charcoal0o, their
data for long unburned soils ranged from 1.67 to 4.91 percent.
Soils having less than 3 or 4 percent organic matter may be
considered as being low in this constituent. The low organic
matter content of well drained soils of this region is further
attested by their consistently light color. The A, horizon, even

SHeyward and Tissot, working in the longleaf pine region, found one
hole or tunnel % to 1 inch in diameter per 4 square feet of soil under
longleaf pine forests. This tally was of holes and tunnels in present or
recent use. Many additional such burrows partially or completely filled
in from disuse were found.
9No study area having a soil heavier in texture than fine sand and pro-
tected from fire for over 20 years was located. In view of this short
period of time for development of the humus layer, it is entirely possible
that definite changes toward a more typical mull will be observed in later
years for the heavier textured soils of the region. In this event, the
horizon now designated "Ai" would probably become the H-layer or mull
horizon. Three areas on fine sandy soil, each protected from fire for at
least 40 years, were studied. The abrupt line of demarcation between the
forest floor and mineral soil failed to indicate a tendency toward typical
mull formation.
However, although the areas forming the basis of this study varied
in length of time protected from fire from 10 to over 50 years, it was
noteworthy that no major differences in the humus layers were recorded.
This indicates early establishment of an' equilibrium between factors
influencing development of the humus layer following protection from fire.
lOThe universal presence of charcoal in all pine forest soils: of the
region is a good indication of the widespread occurrence of fires during
past years. Because of charcoal contamination, ignition loss figures may
be considerably too high.






Florida Agricultural Experiment Station


when constantly worked over by the fauna, remains a light brown
or gray in color. Well drained soils in southern United States
are general low in organic matter because of high temperatures
and heavy rainfall which promote the rapid breakdown of or-
ganic matter.
The loose, penetrable A1 horizon, low in volume weight, which
underlies the typical forest floor under longleaf pine, owes these
properties, therefore, not to organic matter but to the constant
working of an active soil fauna, of which small mammals are
probably the most important members.

MAXIMUM DEPTH OF FOREST FLOOR

Under pure coniferous stands in certain climates the organic
layers may attain great depths. Hesselman (11) mentions raw
humus to a depth of 15 inches under spruce in Sweden. Romell
and Heiberg (25) state that a greasy duff type of humus layer
one foot or more in depth frequently occurs under hemlock or
spruce-balsam in the mountains of northeastern United States.
Such excessive development of the organic layers is usually
highly unfavorable, frequently being accompanied by soil de-
gradation. That this condition does not occur in the longleaf
pine region may be seen from Table 1, in which maximum depths
of the organic layers are given for 14 areas widely spaced over
the region. Data are presented for only 14 of the 42 areas
studied, as complete stand histories and weights of the forest
floor were not available for the remaining areas. No measure-
ments of depth of forest floor, falling outside the range of those
listed, were obtained for the 28 areas omitted from Table 1.
Measurements were made as follows: At four or more spots
selected at random on a given study area, one square foot of the
forest floor was removed by cutting around the edges of a rigid
pattern, one foot square, with a sharp knife. A one-foot metal
ruler was then placed along one edge of the square space left
after removal of the forest floor. The ruler lightly compressed
the loose ends of pine needles and thus afforded a definite mark
from which to measure. The distance from the top of the
mineral soil to the bottom edge of the ruler was recorded as
the thickness of the forest floor.
Although several of the areas visited had been protected from
fire for at least 30 years, it is noteworthy that the greatest






TABLE 1.-MEASUREMENTS OF FOREST FLOOR UNDER CLOSED STANDS OF PINE PROTECTED FROM FIRE.

Approxi- Mean'
mate oven- Age
Area Location years Mean dry Type of of Soil designation
No. protected depth weight pine forest stand
from fire per acre


Summerville, S. C ....................

Waycross, Ga. ............................

Racepond, Ga. ............................

Hazlehurst, Ga. .....................

Cumberland Island, Ga. ..........

Trenton, Fla ..............................

Bartow, Fla. ...........................

Stapleton, Ala. ........................

Flomaton, Ala. ..........................

Wiggins, Miss. ........................

Wiggins, Miss. ..........................

Howison, Miss ..........................

State Line, Miss. ...................


La .............................


Inches

2

2

2Y

21/4

2

2

1%/

22

3/2


Number

14

16

38

30

50-75

15

44

11

15

9

15

20

14

17


Pounds

34475

41677

54833

32074

22375

19878


20070



17189

31306

30057

19590


Longleaf

Slash

Slash-longleaf

Slash

Longleaf-slash

Longleaf

Longleaf

Longleaf

Longleaf

Slash

Longleaf

Longleaf

Slash

Longleaf


Years

25

21

40

30

250

25

250

25

45

9

25

60

9

18


iThese values are doubtless somewhat high due to presence of sand which contaminated the F-layer.


Norfolk fine sandy loam

Leon fine sand

Leon sand

Coxville fine sandy loam

Norfolk fine sand

Blanton fine sand

Eustis fine sand

Norfolk fine sandy loam

Orangeburg fine sandy
loam

Coxville fine sandy loam

Orangeburg fine sandy
loam

Ruston fine sandy loam

Plummer sandy loam

Montrose silt loam


Urania,


,


, ,


.


,






Florida Agricultural Experiment Station


thickness recorded for the forest floor was 31/2 inches." This
area, Flomaton, Alabama (Fig. 1), had not burned for 15 years.
For the Cumberland Island area, unburned for 50 to 75 years
or possibly longer, the forest floor was only 2 inches thick. For
the majority of the 42 study areas the depth was 2 to 21/2 inches.
It is evident that present site factors are of such a nature that
an excessive accumulation of organic materials does not take
place. A comparative balance exists between breakdown and
accumulation of the organic materials comprising the forest
floor. Although this balance is for all practical purposes es-
sentially stable, it is interesting to note that Plice12 mentions
definite cycles of two to three years' duration within which time
accumulation may be noticeably greater than decomposition and
disintegration, and vice versa. These brief periods of unbalance
return to normal because, as pointed out by Romell (22), an
increased supply of organic matter causes an increase in num-
ber of organisms taking part in its breakdown.

RATE OF ACCUMULATION OF FOREST FLOOR
By far the greatest percentage of material comprising the
organic horizons of forest soils consists of leaves or needles.
The following measurements of annual needlefall are, therefore,
of especial value in considering rate of development of the for-
est floor under longleaf pine.
The data in Table 2 are based on monthly collections from 30
individual milacre plots for each density of timber. From this
table it is seen that an annual needlefall of approximately 2,400
to 3,500 pounds per acre, oven-dry weight, may be expected
from second growth longleaf and slash pine. Although these
data were obtained in Florida, there appears to be no reason
why they should not apply to similar stands of timber elsewhere
in the region.
Accumulation of pine litter in stands protected from fire is
rapid. Within three years a loose layer of pine needles and
"Depth of the forest floor on long unburned areas was found to be
very deceiving if gauged only by ocular estimation. During this study
many unburned stands of timber were located through the help of various
foresters. These men invariably far overestimated the thickness of the
forest floor. Four areas, reported as having a forest floor 6 inches in
thickness, were visited. Actual measurements showed no depth to be
greater than 3 inches. Such impressions were doubtless formed while
the observer was walking casually through the forest and examined the
humus layer by means of the toe of his shoe.
12Plice, M. J. Progress report on soil profile studies on forest and
wild land in the Southern Appalachian Mountain region. U. S. Forest Serv.
Rept. 1935. (Unpublished.)







Humus Layer of Longleaf Pine Forest Soils


scattered twigs and bits of bark may accumulate to a depth of
1 to 11/2 inches. Under closed stands, where shade and needle-
fall have combined to smother out herbaceous ground cover,
the litter forms a continuous, even layer. After three years of
protection, depth of litter increases more slowly as the successive
additions of fresh material become more firmly compressed.
During the third year decomposition and disintegration progress
to a stage at which the bottommost needles begin to break down.
Twigs and small limbs up to two inches in diameter are well
rotted by this time, except for the bark, which is more resistant
to decay. By the end of the fifth year the organic horizon is
very pronounced, although at this stage the litter is much more
conspicuous than the incipient F-layer; by this time, however,
five year old needles have been reduced to fragments measuring
between 1/, and 1/4 inch or less in length.
STABLE 2.-ANNUAL NEEDLEFALL IN SLASH AND LONGLEAF PINE
IN NORTHERN FLORIDA.1
Trees Total dry weight of needles
Plot Forest Type per per acre
Number acre I 1932 to 1933 1 1933 to 1934 I 1934 to 1935
Number Pounds Pounds Pounds
0-40 Longleaf pine
second growth 470 2,931 2,970 3,168
0-41 Longleaf pine
second growth 788 2,437........
0-42 Longleaf pine
second growth 972 2,957 ...........
0-58 Slash pine
second growth 517 ....... 3,494 3,540
0-59 Longleaf pine
second growth 360 ...... 2,307 2,513

]These data apply to the 12-month period August to August.

It is at present difficult to state with certainty how long a
time is necessary for the establishment of a balance between
accumulation and decomposition of litter. As already men-
tioned, it is reasonable to believe that decomposition and dis-
integration processes vary in intensity from year to year accord-
ing to climatological factors, particularly conditions of moisture
and temperature. Over periods of 10 years or more, however,
it is probable that such a balance does exist. From the pre-
Sceding data a few generalizations seem warranted. It should






Florida Agricultural Experiment Station


be possible to obtain a fair estimate of the time necessary for
the establishment of a balance between decomposition and ac-
cumulation by dividing total weight of litter and F-layer per
acre (Table 1) by mean annual litterfall per acre (Table 2).
Provided such an approximation is applied to areas on which
this balance already exists, no serious error should result. From
repeated observations and field measurements of depth of the
forest floor it appeared that Area 3 of Table 1 may be justifiably
so treated. Dividing the 54,833 pounds by 3,500 pounds, the
approximate mean value in pounds per year for slash pine in
Table 2, gives a quotient of 16 years. Area 3 was a moist site
and the F-layer was much heavier than average. A similar
computation for Area 5, using Plot 0-41 as a base, since both
are open grown stands, gives 9 years. Since the weights in
Table 1 are doubtless slightly high due to contamination with
sand as already mentioned, these estimates of time of maturity
of the forest floor are likewise somewhat high. Further com-
putations reveal that the time for maturity of the forest floor
of all remaining areas, except numbers 10 and 13, falls between
8 and 12 years; the young age of the stand on both of these
areas accounts for this deviation. It should be pointed out that,
for young stands such as those on areas 10 and 13, actual time
of protection from fire is apt to be misleading in judging re-
quired time for the balance between decomposition and accumu-
lation of litter. On many sites in the region slash pine repro-
duction becomes established from one to three years following
protection from fire; on others time for establishment may be
longer. However, even under the dense stands typical of slash
pine the quantity of litter added to the soil is inappreciable
until the stand is six to eight feet high, a height attained at
an age of about 5 years on most sites. For this reason the
litter alone, the F-layer being in its incipiency, on areas 10 and
13 represented only about 5 years' accumulation.
Summarizing the foregoing remarks it may be stated that
an approximate balance between accumulation and decomposi-
tion of litter under longleaf and slash pines occurred during
the period 8 to 16 years, and in most stands probably between
8 and 10 years. The most important conditions determining
this time are probably stand density, age of stand, and condi-
tions of moisture and temperature.
It should be pointed out that, although there are no further
marked changes in the development of the forest floor after it
attains maturity, changes in the humus layer and in the under-






Humus Layer of Longleaf Pine Forest Soils


lying mineral soil due to the soil fauna doubtless continue for
a longer period. In other words, the fauna may continue to
increase soil penetrability and porosity and to decrease volume
weight in the direction of constants for these values. There
is no reason to believe that these constant values would be
attained simultaneously with maturity of the forest floor. Pos-
sibility of such activity, with resultant modifications in the
humus layer, has already been intimated (footnote 8). It is
recognized, of course, that, in the soil, conditions of balance or
equilibria are always dynamic, and minor deviations in one
direction or another may occur frequently. However, under
the same general site conditions a change in one direction is
sooner or later followed by a counterchange, thus tending to
preserve the original balance.

CHEMICAL COMPOSITION OF THE HUMUS LAYER

Of much importance to forest growth are the chemical char-
acteristics of the humus layer. This is true because it is only
through the decomposition of the organic matter on the soil
surface that the majority of the nutrient materials taken up
by plant roots are returned to the soil. The carbon-nitrogen ratio
and the percentage of mineral constituents are known to in-
fluence the rate of decomposition of organic matter and nitrogen
transformation (26, 28, 31). Partial chemical analyses of litter,
F-layer, and At horizon from areas widely spaced over the long-
leaf pine region are presented in Table 3.13 These data are based
on analyses of one composite sample, each composite consisting
of six individual samples distributed at random over the area
being studied. No pH values are given; however, numerous
pH determinations made on the F-layer at other times have
shown pH values from 3.39 to 5.00. These values range con-
sistently from 0.25 to 1.00 pH unit lower than those of the A1
horizon of the corresponding soil.
The wide C:N ratio characteristic of forest floors in general
and of the underlying A1 horizon is again brought out by the
present data. Lunt (15) points out that the conventional factor
1.724 for converting carbon to organic matter is too low for
materials having a high content of carbohydrates, such as the
organic horizons of forest soils. This investigator found that
1iAll chemical analyses were run according to standard methods as
given in "Methods of Analysis of the Association of Official Agricultural
Chemists", Washington, 1930, third edition.








TABLE 3.-PARTIAL CHEMICAL ANALYSES OF LITTER, F-LAYER, AND Ai HORIZON OF LONGLEAF PINE FOREST SOILS.

Calculated organic
matter
Total Total Loss on Mag- Phos- Lunt's
Description of Study Area Carbon Nitrogen C:N Ignition Calcium nesium Potassium phorus Factor factors
S1.724 (1.89 and
1.85)


Longleaf pine Litter
Summerville, S. C. F-layer
Norfolk fine sandy loam Ai

Slash pine Litter
Suwannee Lake, Ga. F-layer
Leon fine sand A,

Longleaf pine Litter
Cowhouse Island, Ga. F-layer
Leon sand Al

Slash pine Litter
Starke, Fla. F-layer
Leon fine sand A.

Slash-Loblolly Litter
o aiford, Fla. F-layer
Blanton fine sand At

Longleaf pine Litter
Glen St. Mary, Fla. F-layer
Coxville loamy fine sand Ax

Longleaf-Hardwoods Litter
Madison, Fla. F-layer
Orangeburg fine sandy loam At

Slash pine Litter
Lake Butler, Fla. F-layer
Portsmouth loamy fine sand A.

Longleaf pine Litter
Bartow, Fla. F-layer
Eustis fine sand A,

Longleaf pine Litter
Newberry, Fla. F-layer
Norfolk fine sand Al

Longleaf pine Litter
Mt. Dora, Fla. F-layer
Norfolk fine sand A.


Percent

51.07
31.64
4.73

52.57
33.62
4.49

51.51
35.91
1.62

49.96
23.68
2.08

50.02
16.73
1.23

49.76
21.75
2.02

49.82
15.97
3.45

53.28
31.61
4.02

51.00
21.82
2.95

51.26
13.32
1.14

50.87
20.77
1.74


Percent

.360
.530
.137

.475
.645
.109

.467
.561
.033

.555
.590
.078

.535
.452
.052

.543
.481
.041

.883
.492
.143

.465
.808
.181

.730
.578
.103

.535
.413
.057

.652
.661
.065


141.9
59.7
34.6

110.7
52.1
41.2

110.3
64.0
49.1

90.0
40.1
26.7

93.0
37.0
23.6

91.6
45.2
49.3

56.4
32.4
24.1

114.6
39.1
22.2

69.9
37.8
28.6

95.8
32.2
20.0

78.0
31.4
26.8


Percent

97.49
55.46
8.36

97.30
60.51
7.50

98.25
59.74
2.52

97.70
44.70

97.09
29.40

96.74
36.31

92.26
31.30

97.88
59.67

95.57
45.19


96.97
30.25

97.39
42.19


Percent











.365
.300

.343
.263

.490
.410


.854
.452

.406
.241

.533
.520

.545
.325

.427
.391


Percent j Percent


Percent











.110
.085

.130
.066

.151
.087

.166
.087

.142
.057

.147
.081

.121
.061

.139
.090


88.04
54.55

90.63
57.96

88.80
61.91

86.13
40.82

86.23
28.84


85.79
37.50

85.89
27.53

91.85
54.50

87.92
37.62

88.37
22.96

87.70
35.81


96.52
58.53

99.36
62.20

97.35
66.43

94.42
43.81

94.54
30.95

94.05
40.24

94.16
29.54

100.70
58.48

96.39
40.37

96.88
24.64

:96.14
'38.42


.055
.038

.083
.033

.041
.027


.099
.135

.045
.048


.086
.296


.046
.049

.063
.039


1 ------ ------ ____ ___________






TABLE 3.-PARTIAL CHEMICAL ANALYSES OF LITTER, F-LAYER, AND A. HORIZON OF LONGLEAF PINE FOREST SOILS.-Continued.


------Ii

Total Total
Description of Study Area Carbon Nitrogen C:N


Percent Percent

Longleaf pine Litter 48.32 .434 111.3
Mobile, Ala. F-layer 24.13 .541 44.6
Norfolk fine sandy loam A. 2.80 .061 45.9
Longleaf pine Litter 48.13 .425 113.2
Stapleton, Ala. F-layer 23.07 .436 54.3
Norfolk fine sandy loam At 2.30 .076 30.3

Longleaf pine Litter 46.76 .492 95.0
Van Cleave, Miss. F-layer 27.41 .561 48.8
Norfolk sandy loam At 2.86 .098 29.2
Slash pine Litter 48.91 .558 87.6
Van Cleave, Miss. F-layer 24.56 .380 64.6
Coxville fine sandy loam A. 3.47 .103 33.7
S Slash pine Litter 49.89 .453 111.0
. Van Cleave, Miss. F-layer 28.40 .583 48.7
Coxville fine sandy loam Al 2.43 .076 32.0
Longleaf pine Litter 48.45 .450 107.7
Biloxi, Miss. F-layer 29.36 .557 52.7
Orangeburg fine sandy loam A. 3.38 .077 43.9
Longleaf pine Litter 47.91 .445 107.7
McNeill, Miss. F-layer 16.53 .440 37.6
Orangeburg fine sandy loam Ai 2.04 .067 30.4

Loblolly Litter 55.53 .427 130.0
Wiggins, Miss. F-layer 36.27 .590 61.5
Orangeburg fine sandy loam At 1.99 .060 33.2

Slash pine Litter 55.66 .565 98.5
State Line, Miss. F-layer 25.44 .455 55.9
Plummer loamy sand Ai 1.84 .066 27.9


Means Litter: 50.53+ .54 .522+.027 100.7+4.39
Means F-layer: 25.13+1.49 .538+.022 47.0-2.43
Means A,: 2.63- .23 .084--.008 32.6+1.98


d organic
hitter


i


SCalculate
I ma
Loss on Mag- Phos-
Ignition Calcium nes:um |Potassium phorus Factor
S1.724

Percent Percent Percent Percent Percent

95.72 .421 .099 .049 .028 83.30
50.18 .539 .107 .038 .027 41.60

96.83 .291 .079 .045 .026 82.98
42.72 .434 .102" .029 .020 40.81

93.69 .419 .086 .042 .031 80.61
55.88 .642 .147 .043 .030 47.25

95.26 .430 .105 .037 .025 84.32
40.49 .343 .087 .041 .015 42.34

96.79 .318 .100 .039 .021 86.01
53.50 .386 .078 .027 .025 48.96

95.21 .412 .090 .046 .028 83.53
58.11 .573 .095 .029 .031 50.62

95.98 .413 .092 .050 .031 82.60
33.98 .470 .078 .048 .020 28.50

96.70 ...... ...... .... 95.73
64.43 ...... .......... ...... 62.53
3.17 ...... ... ........

95.66 ...... .. ...... .... 95.96
41.20 ...... .... ..... ...... 42.86
2.93 ...... ...... ......


96.32-+ .356 .444--.034 .117--.007 .056+.004 I.047-.006
46.76,2.506 .419--.030 1.087.006 .035.007 .056---.018
4.90- 1 .246 ...... ...... I ...... ...... ...... .... ...... ...


SLunt's
factors
(1.89 and
1.85)


91.32
44.64

90.96
43.79

88.38
50.71

92.44
45.44

94.29
52.54

91.57
54.32

90.55
30.58

104.95
67.10

105.20
47.06


~






Florida Agricultural Experiment Station


the factors 1.8914 and 1.85 are more nearly correct for litter
and F-layer, respectively. In the F-layer, consisting of organic
materials in an active state of decomposition, materials high
in carbohydrates decompose readily with a conservation of nitro-
gen within the materials high in proteins. Waksman (29) states
that, although Lunt's criticism is justified that the factor 1.724
is too low for use in organic horizons of forest soils, the conven-
tional factor should be used in preference to Lunt's figures.
Waksman infers that, whereas Lunt's figures are more ac-
curate than the conventional factor for the particular forests
in which Lunt worked, the conventional factor had best be used
for other areas, unless a new factor is calculated for each dis-
tinct forest. It is noteworthy, therefore, that factors for litter
and F-layer calculated for the longleaf pine region were prac-
tically identical with Lunt's factors. A factor of 1.909+0.019215
for 20 samples, compared with Lunt's factor of 1.8920.0084
for 12 samples, was obtained for litter. Similarly, a factor pf
1.8820.0394 for 20 samples, as compared with Lunt's factor
of 1.8540.0056 for 55 samples, was obtained for the F-layer.
The differences between the two factors for litter, when com-
pared with their errors, were not statistically significant; like-
wise there was no statistical difference between factors for the
F-layer. However, a difference of 0.1850.0192 was found be-
tween the litter factor computed from the present data and the
conventional 1.724 and a difference of 0.1580.0394 between the
F-layer factor and 1.724. This comparison shows that beyond
a doubt the differences were real. The small error of the mean
for Lunt's data, as compared with that for the present data,
can no doubt be attributed to the fact that Lunt worked in a
much more restricted territory than that included in the present
study.
The C:N ratios of litter and of F-layer, 100.74.39 and
47.02.43, respectively, are much wider than similar values for
northeastern forest soils reported by Morgan and Lunt (18).
Their values for litter range from 45.0 for a strongly podsolized
type to 81.8 for a mull type, with a general mean for all values
of 61.4. Similarly, their values for F-layer ranged from 22.2
for a strong podsol type to 64.7 for a raw humus type, with a
general mean of 37.9. Waksman and Hutchings (30) present
the following C:N ratios for a raw humus podsol under white
14Calculated by dividing values for loss on ignition by carbon.
15Standard error of difference. Lunt's probable error changed to stan-
dard error by dividing by 0.6745.






Humus Layer of Longleaf Pine Forest Soils


pine and hemlock: 59.5 for litter and 24.7 for F-layer. The
much wider C:N ratio of the litter and F-layer of longleaf forest
soils as compared with northern soils appears to be due to the
low nitrogen content of the longleaf soils. Analyses of litter
and F-layer showed 0.522-0.027 percent and 0.5380.022 per-
cent nitrogen, respectively.
In addition to being low in nitrogen the organic horizons of
longleaf pine soils are also somewhat low in calcium when com-
pared with soils of more northern regions. Morgan and Lunt
(18), in Connecticut, reported between 0.76 and 1.28 percent
total calcium for forest litter and from 0.60 to 1.07 percent for
F-layer. However, Gartska (7), working in the same region,
reported from 0.35 to 0.73 percent calcium in litter from pitch
and white pine, respectively. The variation between Gartska's
data and that of Morgan and Lunt is not surprising, as it is
well known that there is considerable variation in the chemical
composition of litter from the same forest species. This fact
is further brought out by Plice (20), who, in addition, reported
the following analyses for calcium in coniferous litter from New
York: 1.1 percent for jack pine, 0.5 to 0.8 percent for pitch
pine, and 0.3 to 0.4 for red pine. Alway et al. (2), working in
Minnesota, reported from 1.04 to 1.41 percent calcium in pine
litter and from 1.16 to 1.41 percent in the duff or F-layer. Alway
and Zon (3), working in jack and Norway pine in Minnesota,
found an approximate average of 0.9 percent calcium for litter
from five plots. These investigators presented the following
analyses of pine litter taken from Ebermayer's studies in Europe:
Ash 1.46 percent, K20 0.15 percent, CaO 0.59 percent, P205 0.12
percent. Corresponding analyses for longleaf and slash pine
litter calculated from Table 3 are: Ash 3.68 percent, K20 0.07
percent, CaO 0.62 percent, and P205 0.11 percent.

SUMMARY
Where longleaf pine forests are subjected to recurrent fires,
a type of humus layer more typical of grassland than of forest
occurs. The humus layer consists of a compact horizon from 2
to 4 inches thick, frequently but slightly darker than the under-
lying soil. The main source of organic matter is from roots
of herbaceous plants, chiefly perennial grasses. The forest stand
itself exerts little or no influence on the humus type, since all
litter is soon consumed by fire. This type of humus layer is
essentially a "fire climax" in that it has developed under the






Florida Agricultural Experiment Station


influence of repeated fires; and, although it has probably been
constant in character for past generations, it is very susceptible
to changes following exclusion of fire.
When protected from fire for 10 years or longer, well stocked
pine forests of the region develop a distinctly different humus
layer. This humus layer exhibits characteristics intermediate
between those of mull and mor.
The humus layer under fire protection typically consists of
an F-layer from /2 to 11/ inches in thickness resting directly
on mineral soil. No continuous H-layer occurs, although local
pockets less than one foot in diameter and mull-like in char-
acter are found. The transition from F-layer to mineral soil
is abrupt. A layer of litter from %4, to 11/ inches thick over-
lies the humus layer.
Intense animal activity occurs in the underlying mineral soil
to a depth of 2 to 3 inches. As a result the soil is extremely
porous and penetrable, and small portions not over 4 inches in
diameter frequently have a volume weight of less than unity.
On soils heavier in texture than fine sand the great activity of
the soil fauna has imparted a slight but definite mull structure
to the topmost mineral soil. Subsequent examinations over a
period of years may reveal that the horizon now generally
designated as A1 may more nearly correctly be called the H-layer
of a mull humus type. The mull-like condition is less pro-
nounced in sandy soil types.
A period of 8 to 12 years is necessary for the establishment
of an approximate balance between accumulation and decom-
position of the forest floor. After this period no further increase
in depth or weight of forest floor occurs.
Annual needlefall in second growth stands of slash and long-
leaf pine is from 2,400 to 3,500 pounds per acre.
A total forest floor of from 20,000 to 55,000 pounds per acre
may accumulate in forests protected from fire for 10 years or
longer, after which time little or no further increase in total
quantity occurs.
Litter and F-layer are characterized by extremely wide C:N
ratios, these values being 100.7-4.39 and 47.02.43, respectively.
Compared with those of other regions in this country, the or-
ganic layers of pine forest soils of the longleaf pine region are
low in nitrogen and calcium.
The conventional factor 1.724 for obtaining percent organic
matter from percent carbon is too low for litter and F-layer






Humus Layer of Longleaf Pine Forest Soils


of longleaf pine forest soils. The new factors computed are
1.909 for litter and 1.882 for F-layer. These factors are con-
sistent with those proposed by Lunt (15) for Northeastern
forest soils.
Physical soil conditions under the humus layer following pro-
tection from fire may be regarded as favorable for plant growth.
The forest floor offers an excellent cover and habitat for an
active soil fauna, and as a result the mineral soil is loose,
crumbly, and very penetrable.
The humus layer on areas protected from fire appears to be
essentially a healthy soil condition. A fairly rapid decomposi-
tion of organic matter occurs, there being no tendency toward
development of raw humus and the accompanying soil degrada-
tion. At the same time, the forest floor is sufficiently developed
to conserve moisture and to prevent mechanical compacting of
the soil surface.

LITERATURE CITED

1. ALWAY, F. J., and J. KITTREDGE, JR. The forest floor under stands
of aspen and paper birch. Soil Sci. 35: 307-312. 1933.
2. ALWAYS, F. J., J. KITTREDGE, JR., and W. J. METHLEY. Composition of
the forest floor layers under different forest types on the same soil
type. Soil Sci. 35: 387-398. 1933.
3. ALWAY, F. J., and R. ZON. Quantity and nutrient contents of pine
leaf litter. Jour. Forestry 28: 715-727. 1930.
4. BORNEBUSCH, C. H. The fauna of forest soil. Internatl. Gong. Forest
Expt. Stas. (Stockholm) Proc. 1929: 541-545. 1930.
5. Et Udhugningsforsoeg I Roedgran. [Thinning experi-
ments in red spruce forests.] Forstl. Forsogsv. Danmark 13: (2):
117-210. 1933. [In Danish. U. S. Forest Serv. Transl. 193, 73 pp.,
illus. 1934.]
6. FISHER, R. T. Soil changes and silviculture on the Harvard Forest.
Ecology 9: 6-11. 1928.
7. GARTSKA, W. U. The calcium content of Connecticut forest litter.
Jour. Forestry 30: 396-405. 1932.
8. GRIFFITH, B. G., E. W. HARTWELL, and T. E. SHAW. The evolution
of soils as affected by the old field white pine-mixed hardwood suc-
cession in central New England. Harvard Forest Bull. 15. 1930.
9. HASSENKAMP, W. Der Einfluss von Standort und Wirtschaft auf die
Rohhumusbildung in der Oberforsterei Erdmannshausen (Neubruch-
hausen). Ztschr. Forst u. Jagdw. 60: 3-35. 1928. [U. S. Forest
Serv. Transl. 150, 36 pp., illus. 1934.]







Florida Agricultural Experiment Station


10. HEIMBURGER, C. C. Forest-type studies in the Adirondack region.
N. Y. (Cornell) Agr. Expt. Sta. Mem. 165. 1934.

11. HESSELMAN, H. Studien fiber die Humusdecke des Nadelwaldes, ihre
Eigenschaften und deren Abhingigkeit vom Waldbau. [Studies of
the humus layers of coniferous forests, their peculiarities, and their
dependence upon silviculture.] Meddel. Statens Skogsf6rs6kanst
[Sweden] 22:5: 169-552. 1926. [German summary pp. 508-552.]

12. HEYWARD, F. Soil changes associated with forest fires in the long-
leaf pine region of the South. Amer. Soil Survey Assoc. Bull.
17: 41-42. 1936.

13. HEYWARD, F., and R. M. BARNETTE. Effect of frequent fires on chemi-
cal composition of forest soils in the longleaf pine region. Fla.
Agr. Expt. Sta. (Tech.) Bull. 265. 1934.

14. HICOCK, H. W., M. F. MORGAN, H. J. LUTZ, H. BULL, and H. A. LUNT.
The relation of forest composition and rate of growth to certain
soil characters. Conn. Agr. Expt. Sta. Bull. 330. 1931.

15. LUNT, H. A. The carbon-organic matter factor in forest soil humus.
Soil Sci. 32: 27-33. 1931.

16. Definitions of forest humus types. Amer. Soil Survey
Assoc. Bull. 17: 43-44. 1936.

17. Profile characteristics of New England forest soils.
Conn. Agr. Expt. Sta. Bull. 342. 1932.

18. MORGAN, M. F., and H. A. LUNT. The r6le of organic matter in the
classification of forest soils. Jour. Amer. Soc. Agron. 24: 655-662.
1932.

19. MULLER, P. E. Studien fiber die natirlichen Humusformen und deren
Einwirkung auf Vegetation und Boden. Berlin. 1887.

20. PLICE, M. J. Acidity, antacid buffering, and nutrient content of forest
litter in relation to humus and soil. N. Y. (Cornell) Agr. Expt.
Sta. Mem. 166. 1934.

21. POWERS, W. L., and W. B. BOLLEN. The chemical and biological nature
of certain forest soils. Soil Sci. 40: 321-329. 1935.

22. ROMELL, L. G. Ecological problems of the humus layer in the forest.
N. Y. (Cornell) Agr. Expt. Sta. Mem. 170. 1935.

23. An example of myriapods as mull former. Ecology
16: 67-71. 1935.

24. Mull and duff as biotic equilibria. Soil Sci. 34:
161-188. 1932.

25. ROMELL, L. G., and S. O. HEIBERG. Types of humus layer in the
forests of northeastern United States. Ecology 12: 567-608. 1931.







Humus Layer of Longleaf Pine Forest Soils


26. SALTER, F. J. The carbon-nitrogen ratio in relation to the accumula-
tion of organic matter in soils. Soil Sci. 31: 413-430. 1931.

27. STICKEL, P. W. Physical characteristics and silvicultural importance
of podsol soil. Ecology 9: 176-187. 1928.
28. TENNEY, F. G., and S. A. WAKSMAN. Composition of natural organic
materials and their decomposition in the soil. iv. The nature and
rapidity of decomposition of the various organic complexes in dif-
ferent plant materials, under aerobic conditions. Soil Sci. 28: 55-84.
1929.
29. WAKSMAN, S. A. Humus; origin, chemical composition, and importance
in nature. Williams & Wilkins Co. 1936.
30. WAKSMAN, S. A., and I. J. HUTCHINGS. Chemical- nature of organic
matter in different soil types. Soil Sci. 40: 347-363. 1935.
31. WAKSMAN, S. A., and F. G. TENNEY. Composition of natural organic
materials and their decomposition in the soil. iii. The influence of
nature of plant upon the rapidity of its decomposition. Soil Sci.
26: 155-171. 1928.
32. WESTVELD, R. H. The relation of certain soil characteristics to forest
growth and composition in the northern hardwood forest of northern
Michigan. Mich. Agr. Expt. Sta. Tech. Bull. 135. 1933.
33. WIEDEMANN, E. tjber die Beziehungen des forstlichen Standortes zu
dem Wachstum und dem Wirtschaftserfolg im Walde. [On the rela-
tions of site to the growth and yield of the forest.] Deut. Forsch.
24: 5-103. 1934. [U. S. Forest Serv. Transl. 222, 70 pp. 1936.]









HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
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