Livestock importantly affected the trend of succession. The tendency
of grazing animals to hold back the forest by stripping the foliage
from young trees and killing them is selective, however; the several
kinds of trees differ in their tolerance to browsing and in their
palatability to animals. The kind of animal and the season and
intensity of use also have important bearing on the ultimate effect.
Several kinds of shrubs and small trees seem to be especially
susceptible to damage by browsing; chinquapin oak, crab-apple, plum,
hazel, dogwood, prickly ash, and paw paw were found to be either
absent entirely from the parts of the woodland that were heavily used
by stock, or much scarcer than they were on adjacent unbrowsed areas.
Some woody plants that are even more susceptible may have been
completely eliminated by browsing.
In the thirties when most of the woodland area was fenced off and
protected from grazing, three wooded hillside areas of a few acres
each, were maintained as connecting strips between the pastures of the
hilltops and those of the bottomlands. These areas were utilized only
at certain seasons, but by 1948 the effect of trampling and heavy
browsing by livestock was conspicuous. Herbaceous ground vegetation
was almost lacking and low woody vegetation was also scarce, in
contrast to the parts of the woodland that were adjacent but separated
by fences that excluded livestock. The contrast was perhaps heightened
along the fences because the animals tended to follow along the fence
lines and their effects were concentrated there.
Table 4.--Numbers of Young Trees of Various Kinds and Sizes in
1954 on a .919-acre Area Consisting of Six Hillside Strips Each
20 Feet Wide. Each Strip Was Equally Divided by a Fence Line,
Excluding Livestock from One Side During the Period 1934
(Approximately) to 1948.
----------------------------------------------------------------------
|Less than 1/2-inch | 1/2-inch to 4-inch|5-inch to 12-inch
| stem diameter | stem diameter | stem diameter
|-------+---------+-------+---------+-------+---------
| | Percent-| | Percent-| | Percent-
| Total | age in |Total | age in | Total | age in
|number | browsed |number | browsed |number | browsed
| | half | | half | | half
----------------+-------+---------+-------+---------+-------+---------
| | | | | |
Dogwood | 556 | 52.1 | 1058 | 16.4 | |
Redbud | 40 | 42.5 | 102 | 5.9 | |
Elm | 30 | 76.7 | 189 | 27.6 | 99 | 47.5
Hackberry | 131 | 39.7 | 206 | 13.1 | 5 | 20.0
Plum | 26 | 77.0 | 35 | 22.8 | 1 | 100.0
Crab-apple | 11 | 100.0 | 46 | 37.0 | |
Red haw | 1 | 100.0 | 33 | 48.5 | 9 | 75.8
Walnut | 7 | 28.6 | 32 | 43.7 | 26 | 61.5
Honey locust | 2 | 100.0 | 20 | 15.0 | 11 | 27.3
Osage orange | 1 | 100.0 | 7 | 57.1 | 2 | 50.0
Shagbark hickory| 3 | 100.0 | 42 | 73.8 | 44 | 40.9
Chestnut oak | | | 26 | 30.8 | 24 | 58.2
Chinquapin oak | | | 12 | 100.0 | 1 | 100.0
Coffee-tree | | | 11 | 18.1 | 8 | 12.5
Ailanthus | 6 | 33.3 | 65 | 26.1 | 3 | 100.0
Black oak | | | 5 | 40.0 | 7 | 16.6
American ash | 21 | 100.0 | 3 | 33.3 | |
Paw paw | 12 | | 61 | 27.8 | |
----------------+-------+---------+-------+---------+-------+---------
In 1954 ten-foot wide strips were sampled on both sides of the fences.
For both browsed and unbrowsed samples, the strips had a total length
of 4000 feet, each representing an area of .919 acres. Table 4
contrasts the number of young trees per acre on the browsed and
unbrowsed areas, grouped in several size classes. In general the
saplings up to one-fourth inch in diameter were those that had become
established in the five growing seasons since browsing was
discontinued and both areas were protected. For this size group the
numbers were approximately equal, being slightly higher on the browsed
strips. However, in the size group of 1/2 inch to 4 inches in stem
diameter, the trees were nearly three times as abundant on the
unbrowsed areas, and most trees within this size range must have
become established within the time of differing treatments. The
disparity in numbers was great for hackberry, redbud, elm and dogwood
which made up the bulk of the saplings. In the size range 5 to 12
inches most trees antedated the fence, and the unbrowsed portion had
only a few more than the portion that had been browsed.
On the formerly browsed areas clumps of gooseberry bushes were
conspicuous and were computed to cover 3.81 per cent of the area
sampled, versus 2.87 per cent on the unbrowsed area. These thorny
bushes seem to be resistant to browsing, and elsewhere have been noted
in abundance in woodlands heavily used by livestock. The elimination
of competing undergrowth by browsers may be a factor favoring
development of gooseberry clumps. The trend was just the opposite for
fragrant sumac, which was computed to cover 1.94 per cent of the
browsed sample versus 3.23 per cent of the unbrowsed sample.
Greenbrier (_Smilax tamnoides hispida_) was most abundant on the
unbrowsed strips, with seven large clumps, and 56 smaller clumps (10
stems or fewer) as contrasted with five large clumps and 32 smaller
clumps on the browsed strips. There were 32 grapevines (_Vitis
vulpina_) on the unbrowsed strips and only seven on those that were
browsed.