LEAFLET 31
TOPSOIL and
PINE TREES
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ALABAMA'S PIEDMONT
AGRICULTURAL EXPERIMENT STATION
, M-. ALABAMA POLYTECHNIC INSTITUTE
E. V. Smith, Director Auburn, Alabama
MAY 1951
TOPSOIL and PINE TREES
in
ALABAMA'S PIEDMONT
JAMES F. GOGGANS, Assistant Forester
IT IS now possible to estimate the
early height growth that may be ex-
pected of slash and loblolly pine planted
in Alabama's Piedmont.
The Alabama Agricultural Experi-
ment Station recently completed a
study of 5- to 13-year-old pine planta-
tions in the Piedmont. It was found
that the depth of topsoil can be used
to estimate the height growth that may
be expected 8, 10, or 12 years after
planting. This study again brings out
the fact that the fastest growing pines
are on the best soils.
During the past few years, planting
of pine trees has increased greatly.
Today, it is a favored method of refor-
esting idle lands. Loblolly pine and
slash pine are the two trees that have
been planted most in the Piedmont.
Loblolly pine is native to the region
and is commonly known as "old field"
pine. Slash pine, though not native to
the Region, was introduced in large
numbers during the period of the Ci-
vilian Conservation Corps.
HEIGHT GROWTH ESTIMATED
farm TOPSOIL
There are many things that affect
tree growth. However, for young slash
and loblolly pine in the Alabama Pied-
mont, a reasonable estimate of height
growth may be made if the depth of
the topsoil is known.
Gal . .. The color illustration is of
a 12-year-old plantation on an Appling
soil, having an 8- to 10-inch sandy loam
top soil. The tallest trees were 37 to 39
feet when the color photograph was made.
The height growth that may be ex-
pected on a site indicates to a large
extent the volume of timber products
that may be expected from a timber
stand over a period of years. The vol-
ume growth of pine trees is closely re-
lated to their height growth. In even-
aged pine stands, the average total
height of the tallest trees is the com-
monly used standard by which the
quality of a site for growing trees is
judged.
Figure 1 (slash pine) and Figure 2
(loblolly pine) show the estimated av-
erage height of the tallest trees in
plantations for given ages and depths
of topsoil. From the standpoint of early
tree growth that can be expected, all
sites can be divided into four classes.
These classes are:
(a) Poor site, less than 2 inches of
topsoil
(b) Fair site, 2 to 4 inches of top-
soil
(c) Good site, 4 to 8 inches of top-
soil
(d) Excellent site, more than 8
inches of topsoil; also included in this
class are the well-drained bottom land
soils.
Results of this study apply only to
planting sites on the principal soils' of
the Alabama Piedmont. These soils are
well drained. They are easy to recog-
nize because they have red, yellow, or
brown compact clay subsoils. Original-
'These are soils of the Cecil, Appling,
Madison, Lloyd, Coosa and Louisa series.
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Av. Height of Tallest Trees (Feet)
6 8 10 12
PLANTATION AGE (Years)
FIGURE 1. Estimated heights for young slash pine at different ages on poor to excellent sites.
Av. Height of Tallest Trees (Feet)
FIGURE 2. Estimated heights for young loblolly pine at different ages on poor to excellent sites.
6 8 10 12
PLANTATION AGE (Years)
lv these soils had a gray or brown san-
dy loam topsoil layer 12 to 14 inches
deep. Because of erosion the topsoil
layers are now extremely variable in
texture, depth, and color.
HOW TO ESTIMATE
EXPECTED GROWTH
The expected height growth of trees
to be planted on any prospective plant-
ing site may be estimated by use of
Figure 1 for slash pine and Figure 2
for loblolly pine. The tree height, which
will be read at the tip of the trees in
Figure 1 and Figure 2, is the average
height of the tallest trees in a stand.
These are the trees that have a full
open top. Because their growth has
been interfered with least by the other
trees, they are the best trees to use in
judging the quality of the site.
All estimates are made for small uni-
form areas; therefore, large areas are
divided into small areas, the topsoil
depths of which are approximately the
same. If the average depth 
is to be
determined accurately, numerous mea--
surements of the topsoil depth must be
made in each small area.
A measurement of the topsoil depth
can be easily made as follows:
1. Use a ruler and a digging tool,
such as a mattock or shovel
2. Dig through the topsoil layer un-
til compact clay subsoil is reached
3. Measure the thickness of the top-
soil layer.
In most instances the topsoil layer can
be recognized easily from the subsoil
by one or more of the following differ-
ences: (1) the topsoil is gray or light
brown, whereas the subsoil is red or
dark brown; (2) the topsoil has a dif-
ferent feel, it contains sand, and usu-
ally it varies from a sandy loam to a
clay loam, whereas the subsoils are
clays; and (3) the topsoil is loose struc-
tured as compared with the compact,
tight subsoil. On old field sites where
almost all of the topsoil has been lost
by erosion, the only noticeable differ-
ence between topsoil and subsoil is
structure. The topsoil layer may con-
sist of only I or 2 inches of slightly
loose material on top of the hard, com-
pact subsoil.
With the average depth of topsoil
known, one may refer to Figures I or
2 to determine the expected height
growth. Slash and loblolly pines less
than 7 years old do not follow a defi-
nite trend of growth. To estimate ex-
pected height growth, ages 8, 10 or 12
may be used, although the latter two
are the more reliable.
PRODUCTIVITY 4
DIFFERENT SITES
Merchantable volume of forest prod-
ucts produced over the years is the
practical standard by which produc-
tivity of a site is judged. Merchantable
volume refers to the volume of the
trees large enough to be used for such
products as pulpwood, poles, and saw-
logs. Fence posts, fuel wood, and stack
poles usually come from the smaller
non-merehantable trees.
Trees in many of the young planta-
tions studied in the Piedmont were too
small to be cut for pulpwood. However,
many were large enough for fence
posts. Volume of wood produced in
young plantations depends not only on
height growth, which can be estimated,
but on the survival, or number of trees,
and diameter growth.
The total volume and merchantable
volume in plantations studied did not
give a true picture of the relative pro-
ductiveness of the different sites be-
cause the plantations were too young.
These volumes, however, did show
what the sites had produced up to the
time of the study and the differences
in early growth caused by site.
A good example of such differences
was found in the 10-year-old loblolly
pine plantations studied. These plan-
tations were originally planted at a spa-
cing of approximately 6 by 6 feet, or
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1,210 trees per acre. At 10 years of
age, all averaged very close to 1,000
trees per acre, except those on the poor
sites. The plantations on poor sites were
extremely variable, with some having
as few as 400 to 500 trees per acre.
No merchantable volume was cal-
culated for the plantations on the poor
sites, since very few trees were large
enough to be merchantable. It will be
a long time before the plantations on
poor sites can be thinned.
The average merchantable volume of
the plantations on fair sites was 9 cords
of rough wood per acre, while that of
the plantations on good sites was 101/2
cords. None of these plantations was
ready to be thinned.
Those plantations on excellent sites
had an average merchantable volume
of 13 cords of rough wood per acre.
A few of the best plantations had grown
enough to need thinning at the time
of study. The remainder will need
thinning within 2 or 3 years.
Thinning is necessary if these plan-
tations are to produce the most wood
possible on a particular site. The thin-
ing must be done at the right time. Dur-
ing the early life of slash and loblolly
pines and before reaching sawlog size,
a live crown one-third of the height
of the tree should be maintained.
Judging from general observations
in the Piedmont, plantations spaced 6
by 6 feet with 80 per cent survival at
10 years on excellent sites will need
thinning at 10 to 13 years of age. Those
on good sites will need thinning in 13
to 16 years, whereas plantations on
fair sites will need thinning in 16 to
20 years. The amount of wood that
can be removed at the first thinning var-
ies with each plantation. If the trees
are crowded and a thinning is needed,
the average amount that can be re-
moved safely is about one-third of the
merchantable volume. In the case of
the 10-year-old loblolly pine planta-
tions on excellent sites, a yield of about
4 cords per acre could be obtained.
Where there is no knowledge of mer-
chantable volume, a practical guide
is to remove about one-third of the trees
above 4 inches in diameter breast high.
The trees removed should include: (1)
badly diseased and insect infested
trees, (2) crooked and poorly formed
trees, and (3) those trees that should
be removed to give the other trees
growing space.
CONSERVING SOIL IMPORTANT
jo TIMBER GROWING
Because of the rough topography of
the Piedmont Region, soils without
vegetative cover or terraces tend to
erode rapidly. In fact, the soils of this
region have been eroded more severely
than the soils of any other region in
the State.
It is very important that a vegeta-
tive cover be established as soon as
possible after a field is no longer used
for crops. An unprotected excellent
site may erode to such an extent that
it becomes only a fair or even a poor
site within a few years. Figures I and
2 show what site means in terms of
early height growth. However, early
growth is not the only consideration.
Planting costs are higher on a poor site
than on a good site, and the cash re-
turns are slower. Also, the differences
in volumes of forest products that may
be produced on the various sites are
much larger than the differences in
height might indicate. These differ-
ences in volume growth become great-
er as the stands get older. At 50 years
of age, the loss due to erosion might
mean the differences of 20 to 30 feet
in the height of the trees and of 15,000
to 25,000 board feet of lumber per
acre in the final harvest.
Topsoil means fast-growing trees
that return money quickly. From an
economic standpoint, conservation of
topsoil is extremely important. A few
inches of topsoil means the difference
between a slow-growing, poor-yielding
plantation and a vigorous, fast-growing
plantation that will begin to return
money at an early age.
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