Successional
trends were greatly altered. Woody vegetation, already favored by
protection from the prairie fires originally important in the ecology of
this region underwent further development as a result of protection from
browsing. Thickets of shrubs and saplings sprang up throughout the
woodland, forming a dense understory layer beneath the discontinuous
canopy of the relatively scattered mature trees. The composition and
density of the undergrowth varied markedly in different parts of the
woodland. The parts that were formerly most open acquired the most dense
understory. Blackberry, honey locust, osage orange, and prickly ash
formed in places thorny tangles almost impenetrable to humans. This
thicket stage reached its peak in density in the middle to late forties
coinciding approximately with the time of maximum abundance of the rats.
In the past eight years, under continued protection from burning,
cutting and browsing, the forest has developed further; sizable trees 20
feet or more high and up to eight inches in trunk diameter have grown
from seedlings during the period of protection. An almost continuous
canopy of foliage has developed, shading the understory and thinning it
by killing shrubs and saplings. In those situations where the canopy is
most dense, as on north slopes having stands of young hickory averaging
twenty feet high, the understory is now largely lacking, but in other
situations, particularly on south slopes, the understory thickets are
still dense. On the whole, however, habitat conditions have become less
favorable for the woodrat.

Within the woodland the population of woodrats was not evenly
distributed even at its maximum density; only those situations that
provided sufficient overhead shelter were occupied by woodrats. The
hilltop limestone outcrop, which was the refugium of the survivors when
the population was at low ebb, also supported the greatest concentration
when the population was high. The number of individuals living along any
particular stretch of ledge could be determined only by intensive
live-trapping, whereas residences of individuals could be more readily
identified in most other situations away from the ledge. Stick houses of
woodrats are, characteristically, large and dome-shaped in woodland, but
along the ledges they usually lacked this typical form and consisted of
a much smaller accumulation of sticks, often merely filling a small
crevice. Sticks carried into such pla