One of the major points of interest in Platt National Park is the existence of an ecotone, or boundary between two major kinds of ecosystems. This ecotone is unique in that it is not a broad transition but occurs very abruptly within the limited confines of the park. Because of the abrupt and abbreviated nature of this change, it is obvious to anyone who is expecting it and is an excellent example to study and use as a teaching illustration.

The two major ecosystems which meet each other in the park are the eastern deciduous forest and the western short-grass, or steppe-type, prairie. Each of these ecosystems has a core area in which it is most intense in its manifestation. That intensity declines as the distance from each core increases, and between the typical deciduous forest and the short-grass prairie one finds a transitional landscape which has some characteristics of each of its neighboring ecosystems. Neither of these ecosystems, occurring in close proximity in the park, qualify as theoretical or even regional cores representing their communities, but they suffice on a local basis. At this point it is important to note that ecosystems are often named after their dominant forms of vegetation, but this is only a matter of convenience and in no way excludes from the discussion the full range of flora and fauna.

The dense and multilayered vegetation of a climax lowland forest near Travertine Creek.

THE LOWLAND LANDSCAPE

The dominant ecosystem in the lowlands of the park is one of the westernmost extensions of its kind in Oklahoma. It is a southwestern remnant of a huge prehistoric forest which once covered much of the earth's northern hemisphere. Repeated glaciations of the Pleistocene, or "ice age," and increased human settlement in historic times destroyed most of the forest, and the best and richest example long remained that of eastern North America. The forest was once contiguous and of relatively homogeneous composition, but thousands of years of climatic change and plant migration have resulted in regional differences. The southern forest is generally recognized as an oak-hickory community.

A Natural Mature Community

The best example of a mature deciduous forest ecosystem in the park is the dense woodland along Travertine Creek in the Environmental Study Area. There one can see a local climax condition of the eastern deciduous forest. The conditions necessary for this ecosystem are localized in the valley bottom, and so most of this forest is concentrated within several hundred feet of the stream. This is the narrow band of deep alluvial soils which have great water-holding capacity and low drainage gradients. These soil conditions in conjunction with acceptable climatic conditions happen to provide an environment in which the oak-hickory community thrives and outpaces all other ecosystems.

As one strolls along one of the bottomland trails of the Environmental Study Area, the stratification of the forest becomes obvious once the visitor is aware of the characteristics. Most of the dominant trees, which form an overstory some seventy-five to one hundred feet above the ground, are spotted (Texas) oak and bitternut hickory. Both trees have spreading crown tops which reach out for the intense sunlight these trees need. The trunks of both may be as large as two or three feet in diameter. The oak is covered with a dark, ridged, thick bark, while the hickory trunk is protected by a medium-gray, fairly smooth bark. The sycamore is also prevalent where water is abundant, for example, very close to the stream. It is one of the largest trees in size and bulk in a temperate forest. It has a large spreading crown, a trunk perhaps four feet in diameter and a distinctive bark. Most of the bark is light gray and very smooth because it is constantly flaking off. Only very old trees or lower trunks have a thick, dark, furrowed bark.

The next stratum one sees below the dominant overstory trees is the large group of shade tolerant trees of the understory. These trees not only tolerate but prefer less sunlight, lower temperatures, and higher humidity, found in a zone twenty to fifty feet above the ground. The southern hackberry, roughleaf dogwood, and redbud are typical of this group. All these trees have slender trunks and crowns that tend to flatten and spread out to catch all possible sunlight filtering through the overstory.

The shrub stratum includes those plants whose fully mature height is between about two to twenty feet and many tree seedlings whose mature size is much taller. This layer varies a great deal in density and frequency of species from area to area. Commonly seen at this level are the red mulberry, Mexican plum, winged elm, American elm, and dogwood.

The strata lower than shrubs are largely vacant in this portion of Platt because ground litter is so thick and shading so nearly complete that it is difficult for grasses and mosses to grow. That is not to say that this level of the ecosystem has no members nor that all parts of this forest area are without substantial numbers of these plants. It simply means that they do not form a prominent part of the community viewed by man.

As one views the forest, it becomes obvious that not all plants grow in a series of clearly defined upward steps or that all trees of a stratum are of the same height and lushness of growth. One may find immature trees and shrubs progressing through any intermediate level on their way to their "place in the sun." Other plants which transcend the formal strata are climbing vines, such as wild grape. Many of these vines, some as large as one's arm and extending well up into the understory, can be seen along the various trails. There are also other plants, such as the parasite mistletoe which, although less than a yard in diameter, may live at any level on a host tree.

Artificially thinned and cleaned woodland around Rock Creek.

Lowland Forest Variations

The lowland forest have noticeable variations in composition even within a small area like the park. Three of these variations merit mention. The first occurs throughout the park to some degree, but is most marked along the course of Rock Creek. Along the fringes of this stream in the old sand deposits and flood-washed banks that receive more sunlight and water, one finds a lower stratum of annual and perennial herbs, as well as two additional trees. Here the cottonwood and various species of willow thrive on banks and occasional sandbar islands. The cottonwood is a massive, quick-growing tree of the poplar family, which is the sole marker of many intermittent stream channels in arid country. Despite its size, the cottonwood is easily damaged and short-lived, and its thick-barked, craggy trunk provides homes for many kinds of wildlife. The willow is usually a brushy tree with many suckerlike growths that form a dense barrier on stream banks. Because of its density, tenacity, and ease of planting, it is an excellent erosion-control agent.

The valley bottom between the park's main entrance and Rock Creek campground is a man-induced variation of the climax lowland forest. In this part of the park there has been no effort to maintain a natural forest, but rather to create a pleasant parklike atmosphere. An overstory of oak and elm still predominates, but the expected lower strata have largely been eliminated by years of mowing and human activity. Many members of the natural community have been eliminated, and in their place we see imported species which are more compatible with heavy use. Under these conditions the only way this portion of woodland can be perpetuated is through human effort, such as transplantation and protection of seedlings.

The last variation of the lowland forest is the wooded area of Rock Creek campground. Here one sees a community which is constantly struggling to reach the stability of a climax stage. That climax has probably been repeatedly delayed in the past by local flooding, grazing of livestock, or human activity. As a result there is a dense growth of immature overstory and understory tree species, few of which have become dominant enough to shade out lower strata plants that probably could not survive in a climax forest.

The immature woodland in Rock Creek Campground shows small trees reaching for sunlight under intense competition.

Animals of the Lowland Landscape

Thus far in the discussion of the lowland landscape we have been concerned only with the plant life, but it comprises only part of the living ecosystem, even though it is the most obvious and accessible portion of the biological landscape. It forms a large part of the all-important framework, or matrix, within which the various species of animals gather food, find shelter, and raise their young.

The stream banks and immediately adjacent moist areas in the valley are the habitat of several species of amphibians. Most commonly seen is the small leopard frog, which leaps into the stream with a squeak as strangers approach. It feeds on insects near the surface of the streams, and is itself prize fare for several other woodland animals. The frogs, toads, and salamanders of this environment generally live in holes in the muddy banks.

There are many reptiles throughout the lowland, but no poisonous snakes have been seen in the park for several years. Probably they were driven away by the large number of visitors. There are large numbers of rattlesnakes and some cottonmouth snakes in the surrounding area, however. Near the streams are many water snakes, such as diamondback and blotched water snakes. Garter and ribbon snakes also frequent the moist areas. All of these are harmless and feed largely on insects, salamanders, and small frogs. The prairie kingsnake and the black rat snake inhabit the drier lowland and transitional slopes. Both eat large numbers of rodents and other small animals, and the kingsnake has a special appetite for other snakes and lizards. Both of these snakes prowl at night and spend daylight hours in almost any sheltered spot, such as under logs and rocks. Turtles are common in the eastern end of the park, especially the three-toed box turtle and the ornate box turtle. Both of these reptiles are dry-land creatures which will eat almost anything but subsist mostly on grass and leaves. Their hiding places are scratched-out depressions in the soil and ground litter. Bleached shells of the turtles are frequently found on the forest floor.

The mammals in the lowlands of Platt National Park are representative of those found in any eastern lowland forest—with one exception. The exception is the armadillo, which is found largely in Gulf Coast regions and an area through the southern Plains states and whose range is rapidly expanding. This armored animal is a little larger than a house cat and usually lives in a burrow in a ravine or hillside. It feeds largely on insects and grubs, which it roots out of the forest-floor litter. It is very common in the park and is occasionally seen, but is more often detected by the narrow winding furrows it makes each night in the forest litter in search of food.

Figure 15. The raccoon is primarily a nocturnal animal found near streams.

The opossum and the raccoon are common nocturnal forest dwellers whose presence in the park can most readily be detected by their sign. Both feed along stream bottoms where they live mainly on large insects, bird eggs, small mammals, and, in the case of the raccoon, marine animals like frogs, crayfish, and turtles. Their footprints are easily seen along stream banks and on soft soil. The opossum also makes distinctive scratches in the bark of trees while climbing to rest or in search of bird nests to rob.

Squirrels and skunks are also prevalent in the park, including the southern flying squirrel. A small group of these squirrels can be seen near the Travertine Nature Center, leaping and gliding between trees during quiet periods of the morning and evening. They build exterior nests of leaves and twigs or adopt abandoned woodpecker holes. Their feed varies with the season but normally includes nuts, seeds, fruit, and some insects.

The most profuse and varied animal life in the low lands is the bird community. Approximately 150 different species of birds have been seen in or flying over the park, and most of them either live in or temporarily visit the lowland forest environs. More than those of any other animal, the number and composition of the bird population vary seasonally. The complexity of the vegetative community is responsible for the variety in bird life found in the park. It is dense and varied and has multiple strata, which present a great range of habitats. The park is also a protected enclave, where each bird species can sustain itself with minimal disruption.

Each of the bird species has a separate niche which it occupies in the ecosystem. It prefers a certain kind and age of tree for nesting, roosting, and feeding. It also has a preferred stratum in the forest, as well as a bounded area it claims as its own domain. In return for these privileges the bird must contribute to the plant community. He does so by eating insects which attack trees, by pollinating many types of plants, and by carrying the seeds that ensure new generations of habitat-producing plants.

In the lower and understory trees of the forest visitors will frequently see the easily recognized blue jay and the eastern cardinal. Both can be seen sitting on lower branches or dropping to the ground for food. The blue jay is omnivorous and eats berries, seeds, and forest-floor insects, as well as scraps of food left by park visitors. It is very common around the campgrounds in the western end of the park. The cardinal prefers seeds and a little less human company, but it is very common, especially in the eastern half of the park.

The eastern bluebird is a common lowland resident which catches both ground and flying insects for its primary diet and eats wild berries during winter months when insects are in decline. That is just one example of the seasonal adjustment of an ecosystem's food chain. Woodpeckers also control insect pests, particularly those inaccessible to most other birds. It has been estimated that in a well-balanced forest ecosystem woodpeckers find and eat over 90 per cent of the bark-dwelling insects and grubs. Several species, such as the common red-headed and the western red-bellied woodpeckers, can be seen and heard at all times of the day.

An infrequent but easily seen and identified resident of the Rock Creek area is the belted kingfisher. This large, crested, blue-gray bird sits perched on tree branches several feet over the stream, and when it spots a small fish, it dives head first into the stream and emerges with dinner in its beak. It is probably the only fishing bird regularly found in the park. One of the greatest fish eaters, the bald eagle, is rare in this region and has not been seen in the park, though it is sighted occasionally near Lake of the Arbuckles. There are several predators in the park. One of the most conspicuous in the lowland is the northern barred owl. It is a large bird, nearly eighteen inches long. It sits in stream-bottom trees during all times of the day and is not easily disturbed by human activity. It feeds on small mammals, birds, and insects which it swoops down upon. It performs the same role in the thick forest as hawks do in more open terrain.

Last there is the carrion-eating turkey vulture, which one can see on nearly any day gliding over the forest or open country searching for a dead animal. Its keen eyesight finds carrion and soon brings others to share it. It serves the very useful purpose of breaking down and largely removing the carcasses of larger animals. In their absence it would take weeks for insects and decomposing organisms to remove dead animals and return their nutrients to the soil. In this way the vulture is a link in the circular food chain of the ecosystem it inhabits.

All these representative animals, and hundreds of others that could be listed (see Appendix 1), are integral members of the lowland ecosystem and depend to some degree on each other. No less than the birds, all other living things have distinct niches which they must fill—no single member is the keystone of the structure whose presence or absence is paramount—all living organisms share that honor and responsibility.

An area of dense short grass covering the conglomerate upland west of Rock Creek. Trees in the background are on stream valley slopes.

THE UPLAND LANDSCAPE

The upland of Platt National Park, with its slopes and conglomerate-capped hills, forms a totally different physical environment from that of the stream valley, slightly over one hundred feet below. Much of the change is the result of physiographic aridity, a dry environment which is caused by landform factors, such as the steep slopes and extremely permeable conglomerate which mark Platt's uplands. Because it is a different physical environment from the lowlands, there has evolved a different biological environment suitable to the droughty conditions.

Bunch-type short grass on very thin and dry upland soil. Photo by Chester Weems.

Short-Grass Prairie

The most widespread ecosystem of the upland is the short-grass prairie, which has a natural range in dry areas from mid-Oklahoma westward to the High-Plains fringe of the Rocky Mountains in Colorado, and from central Canada southward into Mexico. This community thrives on ten to thirty inches of precipitation a year and withstands both droughts and temperature extremes. In areas of relatively high moisture the short grasses form a fairly dense and uniform soil cover, but on the dry fringes or locally dry areas hardier bunch grasses and other xerophytic, or dryland, plants predominate.

This upland grass land behind Bromide Hill has been invaded by woody shrubs, yucca, prickly pear, and many juniper trees.

Nearly all of the upland along the park's southern boundary is in grassland, but the area atop Bromide Hill between Rock Creek campground and the western Bison Viewpoint is the most accessible. That area would probably have been considered a local climax short-grass community when the site became a park. At that time the only vegetation over its greatest extent was a single stratum of herbs. Most of the surface was covered with blue grama, hairy grama, or the hardy buffalograss. Patches of soil which were too dry to support those solid-cover grasses yielded to bunch grasses of the bluestem family, such as little sand and silver bluestem.

In addition to grasses, the droughty areas of upland soils have supported members of the cactus family and other xerophytes which can survive the harshest local droughts and even expand their range as grasses thin and decline. Foremost in this category is the prickly-pear cactus. This sprawling cactus, with its fleshy and thorn-studded pads and seasonal fruits, is notorious throughout the west for invading pastureland. Ranchers blame the prickly pear for ruining range land, but in truth the cactus can only survive and spread on land where it has little competition. This situation is found on range land which has been abused by man or otherwise ruined for optimal grazing, usually because of poor range management. Occurring along with the prickly pear in Platt National Park is the small echinocereus cactus, a plant two to four inches tall with a rounded, kegshaped body. It is found growing only on the stony soils of the highest and driest portions of the park. More common is the yucca, which is widespread in the clearings of the uplands. It is a plant that reaches a height of one to two feet, with narrow thorn-tipped leaves and an inverted cone-shaped profile.

Prickly-pear cactus. Photo by Chester Weems.

Yucca. Photo by Chester Weems.

Grassland Succession

In the years since the park was established, this apparent climax vegetative scheme has been modified, seemingly through well-intentioned human interference. Parts of the grassland now have substantial areas covered with a shrub stratum and some trees of almost understory dimensions. Encroaching shrub growth is largely seedling oak, chickasaw plum, and sumac. The oak grows singly and slowly, but the plum and sumac quickly form dense thickets on sunny slopes and eventually dominate and shade out the original grasses.

The most conspicuous tree on the upland grassland is the red cedar, or juniper. This tenacious tree will grow nearly anywhere and has apparently found the conglomerate uplands very much to its liking since it was introduced to the park during the 1930's. It spreads across suitable land very quickly because its pea-sized berries are a favorite food for some birds, and the seeds pass through the digestive system unharmed. Another rapidly spreading tree is the brushy persimmon, which seems to have an affinity for abandoned fields and fence rows. It is often found with the small Chickasaw plum tree, and both can be seen covering much of the overgrazed pasture land outside the park's southern boundary. During the spring and early summer months the scrubby plum trees are covered with small but delicious fruit.

The causes of the increase in tree and shrub cover on previous grassland are possibly the same factors which have caused former treeless prairie in other regions of the United States to become wooded in recent decades. Man has overgrazed this grassland to the point where some trees and shrubs are able to gain a foothold in the patches of bare soil in what was once a solid sod cover. Others thrive, as they do in the park, because fences and surrounding human habitation reduce or eliminate browsing, grazing, and trampling by both wild and domestic herbivores. Buffalo, antelope, deer, and cattle will serve such a role if they are allowed to frequent an area. Last, the region is protected from range fires which once claimed much of the prairie each year. Grasses were able to seasonally rejuvenate from seed and sod, but the slower-growing woody plants were eliminated by burning. As a result of those changes in the total environment, there has been an inevitable change in the tenant ecosystem, in this case to a mixed range of grass and shrub.

Animals of the Upland Community

The upland environment is more harsh and restrictive than that of the lowland, resulting in a smaller variety of plant life. Consequently it is the habitat for fewer species of animal life, although still more than the park visitor might expect.

There are two common reptiles in the upland ecosystem of the park. The easiest to see is the six-lined race-runner lizard, which one can frequently spot darting across trails and roads. This lizard, six to nine inches long, feeds on insects and lives in holes or small burrows under rocks and litter on dry upland soils. More difficult to see is the Texas horned lizard, commonly called the horny toad. This broad, flat, sandy-colored lizard will remain nearly motionless for hours while catching ants and other insects near the ground. It likewise uses a convenient depression or hole under vegetation or rocks for its resting place.

The mammals that inhabit the upland are nocturnal creatures, and it is seldom that a visitor will see them unless he is equipped with patience and a good flashlight. The largest mammal population anywhere in the park is probably that of the upland-dwelling white-footed mouse. Each acre of grass and brush is the home of several dozen of the small, seed-eating creatures. Their nests are tiny burrows under rocks or tufts of bunch grass, and the trails where they run at night in search of food appear as a network of furrows through the grass. Another prominent member of the upland margins is the eastern wood rat, sometimes called the pack rat. This rodent is about the size of a house rat. It makes its large outdoor nest under a tree or in a bush or thicket. It builds its nest into a dome-shaped pile of sticks, leaves, and other forest-floor debris. One can see such nests along several of the upland trails in the eastern end of the park. This rat also is a herbivore, living primarily on seeds, nuts, and the wild fruit that he can forage within a short distance of his nest.

Another nocturnal visitor in and near the park's uplands is the coyote, the most common and widespread wild member of the canine family in North America. This animal digs its den or takes over another animal's abandoned burrow on high and relatively open ground. There are probably no dens inside the park, but the animals frequent the uplands in search of food, such as mice and rats. The coyote is therefore a member of the third or fourth trophic level and serves to control the numbers of rodents in its home range. The coyote has no enemy except man's often ill-conceived and unjustified extermination campaigns. Many campers would feel a serious spiritual loss if the coyote's yipping and howling were no longer heard in the night.

Birds, having the greatest mobility of all the animals, visit upland grass and scrub growth in great variety and abundance, depending upon the season and time of day. Those most readily seen there, however, are the birds which depend most directly on those areas for food. Several members of the sparrow family, especially the western field sparrow, are predominant. These small birds usually nest in low trees in or near the grassland and live on the seeds of grasses and other low plants. The cedar waxwing changes locality frequently, but its craving for small fruits and berries makes it a regular resident of juniper-covered uplands, such as Bromide Hill. There it feeds almost exclusively on the small juniper berries and is largely responsible for increasing the range of the juniper by carrying the seeds over wide areas in its digestive tract.

Within the bird family the hawks fill the same role as that of the coyotes on the ground. They are the hunters or predators which appear over the uplands at various times of the day. One which is very frequently seen sitting on poles or trees in the afternoons is the small sparrow hawk. As sunset approaches, this highly maneuverable bird can be seen darting, swooping, or soaring through the air as it catches its principal diet of flying insects. The sharp-shinned hawk can be seen at any time of the day, swooping high and low over the upland margins as it preys on smaller birds. The largest hawk which is common in the park is the red-tailed hawk. This hunter has a wingspread that reaches to as much as four feet and a conspicuously rusty-red tail which makes it one of the easiest hawks to recognize. It nests in the tops of woodland trees but hunts the open grassland, where it can successfully attack animals as large as rabbits. The red-tailed hawk feeds primarily on rodents and is therefore seen late in the afternoon soaring in circles, using its almost uncanny eyesight to spot game that ventures out too early or too boldly.

Figure 16. Example of an upland food chain found in Platt National Park.

The animal life which has been discussed here comprises only a small portion of all the moving creatures in the upland ecosystem. They are, however, fairly representative of the types that live there, the ones visitors might catch some sign of, and ones which point out the basic relationships of the upland food chain.

The greatly simplified diagram shown here illustrates these relationships and the flow of energy and nutrients within the food chain. Of course, any number of other relationships and animals could be portrayed. There are likewise changes in every food chain resulting from seasonal or environmental changes which alter food sources and habitats.

A small segment of the distinct transitional boundary along the conglomerate upland. Note the beginning of grasses and cactus plants where the scrubby tree growth stops. Photo by Chester Weems.

TRANSITIONAL LANDSCAPES

It is obvious that not all of the park's area lies within either the lowland-forest ecosystem or the grassy-upland ecosystem. Narrow as it is, the transitional area, or ecotone, between the two climax types of landscapes has characteristics of its own that will be of interest to the visitor. The location of the transitional ecosystem is largely the area of moderate slopes between the stream valleys and the tops of the conglomerate-capped upland. The most significant determinant of the rate of transition or change of the ecosystem is the increasing physiographic aridity from lowland to upland. The vegetation of this transitional zone consequently represents a spectrum of mesophytic plants (those receiving a well-balanced moisture supply) through xerophytic (dry land) plants.

The Oak-Elm Transitional Community

In the eastern end of the park the transitional community is an oak forest whose principal members are the Texas and chinquapin oak. Texas ash, American elm, and bitternut hickory are important minorities in the upper stories. The understory on the lower slopes is largely redbud, winged elm, and red mulberry; but on upper slopes it is quickly replaced by Mexican plum, shining sumac, and a multitude of herbs. The forest edge forms a distinct line along the lower edge of the conglomerate stratum in this area, with only scattered scrub growth deviating from the natural boundary of the community.

This particular transition zone is the habitat for at least three animals which are seldom seen in other areas of the park. Foremost is the eastern bobwhite quail, which seems to prefer stream-valley ecotones—shade, protective cover, and water are provided by wooded valleys, while the fringing grassland provides the quail with its diet of seeds and small fruits. Coveys of these birds are frequently encountered along the easternmost trails of the Environmental Study Area.

Another visitor or resident of the area is the bobcat, a nocturnal hunter with a range of several miles. It makes its den in nearly any dry, protected place away from human beings and feeds on the small animals of the forest fringe, such as quail and rodents.

According to tracks and other signs the white-tailed deer also makes occasional forays into the east end of the park to drink from the streams or to browse on the leaves and stems of shrubby vegetation. The white-tailed deer is the largest animal that is still running free in the park environment.

The Post Oak Community

The upland slopes in the west-central portion of the park have a vegetation community which is overwhelmingly dominated by the post oak, but nonetheless contains substantial numbers of Texas ash and winged elm. The post oak is a bushy tree of medium size which forms a dense cover over poor upland soils in much of eastern Oklahoma and Texas. It is commonly twenty to forty feet tall in the park and has a trunk diameter of several inches. At one time it was widely used for fence posts and construction timber, hence its name. The understory associated with the post-oak forest is largely seedling or stunted versions of the upperstory, as well as many shrubs, such as Mexican plum and sumac. Native grasses struggle for survival amid the leaf litter of open spaces.

The Short-lobed Oak Community

A last variation in the transition zone is found on the northern rim and face of Bromide Hill, where a community of short-lobed oak mixed with some post oak and Texas ash has formed an almost impenetrable thicket. For some reason the short-lobed oak found this dry outcrop, with all its exposure to the weather elements, to be a very suitable area for growth. It forms the most homogeneous community in the park and is not evident in significant numbers elsewhere. Within that small forest the short-lobed oaks, from ten to fifteen feet in height, dominate in all strata. Only infrequently does the scrub stage of another tree emerge from the forest floor, which is uncharacteristically deep in leaf litter. Junipers and squawbush sumacs flourish in the sunlit fringes of the narrow band of trees.