The thickets formed by crab-apple provide shelter for many kinds of animals. Cottontails, especially, tend to stay in or near these thickets. In autumn the fruits are eaten by them, and in winter, when the ground is covered with snow, the bark is a major food source. Most mature or partly grown trees show old scars near their bases, where the rabbits have attacked them. Often the trees are completely girdled. In years when snow lies on the ground for long periods girdling is extensive and a substantial portion of the trees in the thickets may be killed, but this mortality has been insufficient to check the rapid spread of crab-apple.
The crab-apple is one of the trees preferred as a nesting site by the cardinal. Other birds that frequently use the crab-apple tree as a nest site include the field sparrow, towhee and indigo bunting. White-footed mice, prairie voles and pine voles eat the fruit and seed.
Crataegus mollis.—Red haw occurs over much of the Reservation, both in woodland and former pastures. The trees are scattered, and are not dominant, even on small areas. In the woodland, haw usually grows in the more open situations. Where there are haws in denser woods, they are usually large and old; seemingly they are survivors from a time when the woods were more open. Haw is intolerant of shading, and being of lesser height than any of the climax species, it cannot compete with them. The present wide distribution of haw on the area is secondary, resulting from the extensive cutting of the larger trees and opening up of the woodland. Haw trees are most numerous on south facing slopes that have grown up into thickets in the last 30 years. Here its associates are chiefly honey locust, osage orange, dogwood and elm.
Red haws have been recorded as nest trees of horned owls, yellow-billed cuckoos, cardinals, and fox squirrels. Cavities in the trunks are used by downy woodpeckers, titmice, chickadees and white-footed mice.
Cercis canadensis.—Redbud is abundant in some parts of the woodland. Trees are up to nine inches in diameter and 25 feet high. They grow chiefly in rich soil on hillsides in moist situations. Redbud and dogwood are in part complementary in distribution, each forming an understory in parts of the woodland where the leaf canopy of larger trees is not too dense. However, redbud is more tolerant of shade. In general dogwood grows in the drier, more rocky situations and redbud in better soil and damper sites. In the southeastern part of the Reservation, on a west facing slope, redbud dominates, with smaller numbers of elm, blackjack oak, and dogwood.
Several times nests of yellow-billed cuckoos were found in redbuds. Titmice, chickadees, and red-eyed vireos forage in redbuds on many occasions. Brown creepers forage on the trunks. Titmice, chickadees, and downy woodpeckers used cavities in dead or dying redbuds. However, there is no evidence that this tree is especially attractive to any kind of vertebrate, or plays an important part in the ecology of the area.
Gymnocladus dioica.—Kentucky coffee-tree is one of the less important trees on the area but it is widely distributed. In general it is absent from the denser woods. On limited areas of certain slopes it is the dominant species. The groves sometimes are in nearly pure stands. Slope exposure evidently is not the determining factor in the local distribution as groves have been found on hillsides of varying exposure. The tree seems to flourish where the forest has been opened by cutting of the larger trees. Groves are mainly on the more gently sloping parts of the hillsides, or on the nearly level terrace. There are few coffee-trees more than 12 inches in trunk diameter. The largest tree examined was 27 inches.
In May, groups of orchard orioles (Icterus spurius) have been observed in coffee-trees, seemingly attracted by the blossoms. These concentrations never lasted more than a few days and seemed to involve individuals that were still migrating or newly arrived and not yet established on their territories.
In winter the large pods of this tree are used as food to a limited extent by cottontails. The large hard shelled seeds resist attack by most animals. Seemingly they are used by white-footed mice, as they have often been found stored in the nest cavities of these mice, beneath rocks or in logs.
Gleditsia triacanthos.—Honey locust is at present one of the more important species of trees on the area. There are scattered locusts throughout most parts of the woodland. In the bottomland fields there are groves and scattered trees of medium to large size. On south slopes honey locust, osage orange and red elm form thickets. On hilltops, along woodland edges where fences were installed in the mid-thirties, young honey locusts have become established and are now abundant. Some have grown to a diameter of 8 inches or more. Honey locust is the fastest growing of the trees on the area and therefore has an early advantage in competing with other kinds. A locust of 25-inch diameter cut in 1950 was found to have 32 annual rings, an average of only 1.3 rings per inch as contrasted with an average of 3.8 for all the trees studied, and more than 9 for some of the slowest growing. In open fields, both those used for pasture and those formerly cultivated, young honey locusts have sprung up in abundance since the discontinuance of grazing in 1948. The species is resistant to drought. It seems to have been limited on the area mainly by grazing and shading. The locusts growing in the woods tend to be concentrated near its edges. Those that are deeper in woodland evidently became established after heavy tree-cutting had opened clearings. Locusts in such situations, competing with other hardwoods are of much different form than those growing in the open; the trunks are long and slender and the crowns are narrow.