#Prunus americana.#--Wild plum is a small tree, usually not more than three inches in trunk diameter, nor more than twelve feet high. It tends to grow in dense thickets which are spotty in distribution.

Several of these thickets are in edges of former pastures at the woodland edge. Other extensive thickets are in the following situations: along hilltop rock ledges and encroaching into adjacent prairie on upper south-facing slope maintained as bluestem prairie by mowing and burning, until 1934; along a ravine in formerly cultivated hilltop fields; along tops of steep creek banks at edge of old corn field. In a few situations within the woodland there are dead and dying thickets of wild plum, shaded out by the closing in of the tree canopy, as fast-growing trees such as elm, honey locust, and cherry sprang up in former clearings.

The woodrat lived in several plum thickets that provided the type of shelter from predators that it requires. The bark, fruit and foliage are used as food. In autumn the plums sometimes are the chief food of the opossum. Plum thickets provide the preferred habitat for the Bell vireo (_Vireo bellii_). The white-eyed vireo, field sparrow, tree sparrow, Harris sparrow, and white-throated sparrow (_Zonotrichia albicollis_) also frequently use these thickets.

#Prunus serotina.#--Isolated trees of black cherry six to fifteen inches in trunk diameter, have been noted on various parts of the Reservation at widely scattered points. On a flat hilltop at the southeastern corner of the Reservation there are many large trees of black cherry, which make up a major portion of the stand, and trunks of some are as much as 21 inches in diameter. Other trees in the vicinity are mostly elms and honey locusts, and seemingly the area was more open or perhaps entirely treeless in the recent past. The presence of black cherry in forest often can be interpreted as indicating more open conditions at the time the seedling became established. Black cherry prefers a rich soil and an open habitat; hence it is generally not common in woodlands of northeastern Kansas.

The fruits of black cherry are a favorite food of the opossum, and the seeds have often been noticed in the scats of this animal.

White-footed mice store and eat the seeds. Two trees of black cherry well isolated from other trees except for saplings in low thickets, const.i.tuted the headquarters of a Bell vireo's territory each summer from 1951 through 1955.

#Pyrus ioensis.#--Crab-apple is a small tree, usually less than five inches in trunk diameter and less than 12 feet high. It grows both in woodlands and in former pastures, but chiefly along the line of contact. After removal of livestock in early 1949, crab-apple spread into the edges of hilltop pastures, from the adjacent protected woodland. Each year thickets of encroaching crab-apple have extended farther into the fields, until, in 1955, there were graded series from the trees along the fence, six feet high or more, to the seedlings 30 to 50 feet out in the fields. Dogwood, red haw, and smooth sumac are among the most common a.s.sociates of crab-apple as they share its tendency to invade open land adjacent to the forest.

Evidently the tree is intolerant of browsing by livestock, as few were growing in the pastured areas in 1948, but as soon as livestock were removed these areas were rapidly invaded.

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 a.s.sociates 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 woodp.e.c.k.e.rs, t.i.tmice, 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.

t.i.tmice, chickadees, and red-eyed vireos forage in redbuds on many occasions. Brown creepers forage on the trunks. t.i.tmice, chickadees, and downy woodp.e.c.k.e.rs 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 sh.e.l.led 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.

The south slopes that were originally prairie, were evidently only spa.r.s.ely clothed with trees up until the thirties when livestock were fenced out. Then the abundant growth of shrubs and young trees formed thickets. Honey locust, growing rapidly tended to dominate. The younger locust saplings that were shaded beneath the leaf canopy died in large numbers.

Honey locust plays an important part in the over-all ecology of the area, providing both food and shelter for many kinds of animals. The foliage is well liked by livestock; consequently young trees have little chance of surviving in heavily grazed pastures. Rabbits like both the foliage, and the bark. Often they girdle or injure young trees, and eat the beans. Both the prairie vole and the pine vole often feed upon the inner bark and root crowns of small saplings, sometimes completely undermining them. These voles also store and eat the seeds. Beneath large mature locusts, runway systems and burrows of the pine vole are sometimes much in evidence. As ground vegetation is scanty in these places it seems that the voles are attracted by the abundant supply of locust seeds.

The spiny branches of locusts provide well protected nesting sites that are utilized by various kinds of birds; mourning dove, horned owl, yellow-billed cuckoo, gnatcatcher, cardinal and goldfinch have been recorded nesting in locusts. The wood is relatively soft. The hairy woodp.e.c.k.e.r has been recorded nesting in a cavity which it had dug in a living honey locust, while the black-capped chickadee and red-bellied woodp.e.c.k.e.r have been recorded nesting in cavities in dead limbs. The summer tanager prefers large locusts near the edge of woodland as singing stations.

Fox squirrels also often exploit the spiny protection provided by locust trunks, and build their stick nests in these trees, usually in a fork of the main trunk eight to twelve feet above the ground. Such nest trees often are either isolated or are in groves of other locusts. Presumably the squirrels are attracted to them by the supply of locust seeds.

#Acer Negundo.#--Boxelder probably was not a part of the original flora of the Reservation. The trees present now are few and scattered, and most are not more than eight inches in trunk diameter. The species seems intolerant of shade and does not grow in the denser woodlands. A few are present along the banks of the intermittent streams, and there are others in open woodlands of south slopes. The small patch of bluestem prairie remaining at the northwest corner of the Reservation is being invaded by a variety of shrubs and saplings, and boxelder is by far the most prominent of these invaders, with two hundred seedlings and saplings per acre.

#Ailanthus altissima.#--Tree-of-heaven is an Asiatic species that was introduced early into northeastern Kansas, and has become established locally in the woodland. Most of those on the Reservation are near the central part of the southwestern one-fourth. Concentrated about the site of an old homestead, occupied in the eighteen-seventies, within a few acres, there are dozens of mature trees, up to 22 inches in trunk diameter, and hundreds of saplings. Elsewhere on the Reservation the species is scarce and is represented by isolated trees and scattered clumps at a few places.

#Cornus Drummondi.#--This dogwood is the most abundant tree on the area. However, it scarcely reaches the size of a tree. Most mature examples are 1 to 3 inches in trunk diameter, and rarely more than twelve feet high. Dogwood grows in greatest abundance on dry rocky slopes where other trees are scarce. In small areas it may be the dominant tree, often closely a.s.sociated with chinquapin oak and red elm. In parts of the woodland where there are larger trees, dogwood may form an understory, its development depending largely on the amount of light pa.s.sing through the upper leaf canopy. Where the canopy is dense and nearly continuous, dogwood tends to be eliminated by shading. In some situations where forest has recently closed in, most of the dogwoods are dead or dying. Especially on formerly cut-over north slopes, where oak and hickory have sprung up in a dense stand 20 feet high, with a thick canopy, most of the dogwoods have been eliminated.

On the remaining hillside prairie near the northwest corner of the Reservation, dogwood is the most prominent of the trees and shrubs encroaching onto the area since it has been protected from fire--a period of approximately 20 years. There are dense thickets of dogwood along the borders of the prairie and the woodland edge.

The white-eyed vireo and Bell vireo both forage and nest in thickets of dogwood and other shrubs.

#Fraxinus americana.#--White ash is localized on the Reservation and most of the mature trees are within an area of perhaps three acres on a steep slope of northwest exposure. Several of the largest trees, well over a foot in trunk diameter, grow at the lower limestone outcrop. Ash is most abundant at this level and at the terrace just below it. On the one slope where it is concentrated, ash is one of the most common trees, growing in a.s.sociation with American elm, chestnut oak, black oak, and s.h.a.gbark hickory. This area is one of the most mesic on the Reservation. The soil is usually damp, with thick leaf litter and rich humus. In hilltop fields, formerly cultivated or pastured, saplings of white ash are among the most prominent invaders.

The leaves of this tree and especially its saplings, are favorite foraging places for the tree frog. The groves of this tree provide favorable habitat for the opossum, short-tailed shrew, gray squirrel, and white-footed mouse. Birds that frequent the same habitat include the black-capped chickadee, tufted t.i.tmouse, blue jay, rose-breasted grosbeak (_Pheucticus ludovicia.n.u.s_), yellow-billed cuckoo, red-eyed vireo, gnatcatcher, hairy woodp.e.c.k.e.r, Kentucky warbler, and crested flycatcher (_Myiarchus crinitus_).

[Ill.u.s.tration: PLATE 7

EXPLANATION OF PLATE 7

Upper figure shows gully in southeastern part of Reservation, which has enlarged and deepened greatly in the past 40 years. Heavy precipitation in the summer of 1951 resulted in the undermining and collapse of many large and medium sized trees, as shown in this photograph taken in March, 1956, by H. S. Fitch.

Lower figure shows Cottonwood fifteen feet in circ.u.mference, growing on hilltop near south edge of the Reservation. This is the largest tree on the area. Several exceptionally large black oaks, chestnut oaks, and elms are present on the same hilltop. Photograph taken in December, 1954, by H. S. Fitch.]

[Ill.u.s.tration: PLATE 8

Large American elm at edge of bottomland field in west part of the Reservation. Photograph taken on April 2, 1955, by H. S. Fitch.]

Summary and Conclusions

The University of Kansas Natural History Reservation, in the northeastern corner of Douglas County, Kansas, is situated in an area that originally supported two types of climax vegetation, tall gra.s.s prairie, and hardwood forest. These a.s.sociations were distinct and sharply defined. The present distribution of the different species of trees on the area, supplemented by the data from snails, indicates the approximate distribution of the two original climaxes. The princ.i.p.al climax trees of the original forest were mossy-cup oak (mainly in bottomlands), black walnut, s.h.a.gbark hickory, hackberry, red oak, black oak (mainly on hillsides and hilltop edges), chestnut oak (mainly on rocky upper slopes). Subclimax trees characteristic of marginal situations include: American elm, red elm, white ash, honey locust, osage orange, coffee-tree, red haw, dogwood, redbud, cherry, wild plum and crab-apple. Others characteristic of hydroseral situations include sycamore, willow (of four species), and cottonwood.

In the Kansas River flood plain and small tributary valleys, rich mesophytic forest of predominantly oak-hickory type was present. In somewhat stunted form, and with partial replacement of its species by those of more xeric habit, it extended up onto hillsides sloping north, east or west, and onto the adjacent hilltop edges. Slopes having poor shallow soil and exposures mainly to the south supported chiefly tall gra.s.s prairie, but also had compact clumps of blackjack oak and post oak, usually more or less isolated from other parts of the woodland. Hilltops were mostly treeless (except near their edges) and supported a tall-gra.s.s prairie vegetation. Shrubs and various kinds of small trees must have been a much less conspicuous part of the woodland flora than they are at present, and occurred in small ravines where shelter was inadequate for the larger forest trees, and also along the extensive line of contact between forest and open land.

One of the earliest changes was the destruction of the bottomland forest. With the rapid settlement of the region in the sixties and seventies, lumber was in demand and the supply was limited. The cleared land was productive as pasture. Heavy grazing combined with drought, gradually altered the original tall gra.s.s prairie; the bluestems and other perennial gra.s.ses were replaced by the introduced blue gra.s.s and by various weedy forbs. Prolonged protection from fire permitted encroachment of trees and shrubs into situations where they had not grown previously. Heavy grazing however, tended to hold in check the spread of the woody vegetation.

When the bottomlands had been cut over, lumbering operations were extended onto those hillsides where the better stands of trees were located. The cutting of large, mature oaks, walnuts, and hickories opened up the woodland and permitted large scale encroachment by subclimax species. American elm, especially, sprang up in thickets.

Ash, honey locust, cherry, red haw, crab-apple, dogwood, and the introduced osage orange, thrived and spread in the situations to which they were especially adapted. These species largely replaced the original climax. Some of the trees cut, the oaks, sycamores, and hickories, usually produced fast-growing stump sprouts and competed vigorously with the invaders. At each successive cutting, however, the climax species lost ground. American elm, being tremendously prolific of seed, and only a little less tolerant of shading than its climax compet.i.tors, soon became the dominant tree of the woodlands.