Ecological Communities of Dinosaur National Monument

Riparian Community

Riparian communities in Dinosaur National Monument are usually found at an elevation of around 5,000 feet. At this elevation, riparian communities are a green ribbon winding through the semiarid landscape of the desert shrub community. Within the monument, the primary riparian communities are along the Green and Yampa rivers, as well as smaller streams such as Jones Hole, Cub, and Pool creeks, which emanate from springs and flow into these larger rivers. Organisms living in these riparian communities depend on a nearly continuous supply of water. A continuous supply of water is the limiting factor. The trees and shrubs growing along the rivers create a moist and shady oasis. It is the most productive natural system in Utah and Colorado.

Riparian communities are continually changing because of shifts in the river channel. As the river meanders across the floodplain, sand is deposited along the river shore in bars. The sand bar is gradually colonized by riparian plants. Where these plants become established they protect the sand bar from erosion. As sand bars build up, undercutting of the river bank takes place, and cottonwoods and other riparian plants topple into the river, the cycle of succession beginning once again. Because of the shifting river channel, riparian communities are a mosaic of small plots, each at a different successional stage.

Riparian plants require continual access to water. They are adapted to spring floods and deposits of sand, gravel, and silt. Willow, cottonwoods, box elder, alder, river birch, choke cherry, horsetail, and numerous sedges and grasses are found along rivers and creeks. The exotic tamarisk tree is also abundant in the riparian community. Current, squawbush, elderberry, big sagebrush, snowberry, mock-orange, and ocean spray are shrubs that can be found along creeks.

Beaver, otter, and mink are closely tied to the rivers and their riparian community, as are yellow warblers and rufus-sided towees. Beaver are sometimes dominant because of their dam building and tree-felling activities. In the Green and Yampa rivers native fish have adapted to the warm, turbid water, strong currents, and spring flooding of the river. Fish such as Colorado squawfish (E) (Note: An "(E)" after an organism's name identifies it as an endangered species.), humpback chub (E), bonytail chub (E), razorback sucker (E), roundtail chub, speckled dace, creek chub, redside shiner, sand shiner, mountain sucker, bullhead sucker, white sucker, flannelmouth sucker, and mottled sculpin, are found. Introduced nonnative fish include northern pike, channel catfish, red shiner, fathead minnow, and carp. As of 1997 there were 30 fish species resident to the Green River. Of these, only nine are native fish. Of these nine species, four are listed as endangered, and one is a candidate for listing. Clinging to the river and creek bottoms are abundant aquatic insects including mayflies, caddisflies, stone flies, crane flies, and dragonfly nymphs. On the river surface and along its edge, one can observe mergansers, Canada geese, spotted sandpipers, belted kingfishers, water dippers, swallows, bald eagles (E), and bats. Migrating birds use the riparian community as a resting place in spring and fall. In the evenings, mule deer and bighorn sheep drink and feed along the rivers.

Threats to Riparian Ecosystems:

- Dams and canals block important spawning migration routes of some native fish, cool the water immediately downstream from the dams, which kills newly-hatched native fish, and eliminate "backwaters" needed by young fish. Dams also eliminate spring floods, which help control the intrusion of the exotic tamarisk tree. Tamarisk is crowding out native riparian vegetation. The elimination of spring floods has also prevented the establishment of new cottonwood trees in Lodore Canyon and is causing the narrowing of the Green River channel and the loss of the sand bars and cobble bottom that native fish formerly spawned on. Dams trap sediment, reducing the sediment load of the river downstream and changing river chemistry.

- Introduced exotic fish compete for food and predate young of endangered species, inhibiting their recovery from near extinction.

- Oil pipelines crossing rivers can break releasing crude oil into the water, polluting it and killing aquatic life. This occurred in 1991 on the Yampa River when the squawfish were spawning. Researchers did not find baby squawfish that year.

- Diversion of water from rivers for irrigation and culinary use can make it difficult for both aquatic species and riparian vegetation to survive. Ashley Creek is a local example of this, but an even more dramatic one is the "mighty" Colorado River, where so much water is removed that it no longer flows into the ocean.

- Runoff from agricultural fields contains a chemical stew of salts, fertilizer, and pesticides that pollutes the mainstem rivers. Cattle congregate in the shade of riparian trees and trample young saplings. Eventually the natural under story is destroyed and replaced by weedy species. Cottonwoods disappear since young trees cannot mature and replace old, dying trees.

- Gravel mining and placer mining operations destroy the river bank community as well as the river's cobble bottom. They also increase river turbidity.

- Overuse of the rivers for recreational purposes causes trampling and the elimination of riparian vegetation in popular areas, as well as pollution from human waste. Anglers catch endangered fish and sometimes do not immediately release them back to the river unharmed.

Desert Shrub Community

The desert shrub community extends across the floor of the Uinta Basin from the lowestelevations up to 6,000 feet. The average precipitation is eight inches per year. This lack of water, combined with low temperatures in winter, are the limiting factors. These keep productivity (which is confined to the short summer) low. Soils are also a limiting factor. Soils are typically alkaline because
high evaporation rates during hot summer months lead to a concentration
of salts that can form a white crust on the soil surface.

Desert shrub community plants must be adapted to the hot summer temperatures, cold winters, low humidity, and alkaline soils. Several strategies are used to acquire and conserve moisture. Most of the plants have small, waxy leaves that reduce transpiration. Others have hairy leaves, which reflect light and obstruct the flow of air over the leaf surface, again reducing transpiration. Cacti store moisture in their fleshy stems, while other plants like the sego lily store moisture in an underground tuber. Sagebrush and greasewood send roots deep into the soil to tap the water table, and their woody stems also help to retain moisture. During drought conditions many of these plants shed leaves or become dormant. Greasewood, sagebrush, shadscale, saltbush, bud sagebrush, winterfat, Indian rice grass, galleta grass, and blue gramma grass are the common shrubs and grasses present. Cheat grass, an invasive nonnative, is found in abundance through-out this community.

Animals are also adapted to the harsh environment and general lack of thick cover. Many of the smaller creatures do not need to drink water; they can obtain all they need from the plants that they eat. Many species are nocturnal, while others are active only in the morning and evening. During the heat of the day most will seek shelter in burrows or in the shade of shrubs.

Common herbivores in the desert shrub community include mule deer, pronghorn antelope, elk, desert cottontail, blacktailed jackrabbit, least chipmunk, golden-mantled ground squirrel, white-tailed prairie dog, deer mouse, and sagebrush vole. Carnivores include coyote, red fox, badger, black-footed ferret (E), bald eagle (E), golden eagle, Swainson's hawk, red-tailed hawk, and Northern harrier. Common reptiles include sagebrush lizard, side-blotched lizard, western whiptail, striped whipsnake, gopher snake and bullsnake.

Threats to Desert Shrub Ecosystems.

- Overgrazing and the suppression of lightning-caused fires has resulted in the unnatural spread of sagebrush and juniper trees that now dominate the desert shrub community. Beginning about the turn of the century, and through the 1930s, natural fires were systematically extinguished, and too many livestock were placed on the range. Livestock prefer grazing on grasses and forbs over sagebrush. With the natural controller of sagebrush (fire) eliminated, and the native grasses and forbs overgrazed, the sagebrush began to out compete grasses and shrubs. Today, public land managers use prescribed burns to eliminate sage-brush and stimulate native grasses. However, if livestock are allowed to graze upon burned areas in the spring and summer after a fire, native grasses are suppressed and cheat grass takes over.

- Introduction of nonnative plants disrupts the desert shrub community. Cheat grass was accidentally introduced in the early 1900s and has proliferated. Cheat grass germinates in the fall and grows slowly during the winter. In the spring, when native grasses rely on high soil moisture to grow and produce seed, cheat grass has already used up much of the soil moisture before the native grasses arouse from their winter dormancy. This stresses native grasses which cannot effectively propagate. What's worse, livestock and most wildlife, find cheat grass unpalatable.

- Development of desert shrub areas for human occupation, agriculture, and energy extraction adversely impacts all levels of the community. As native plants are eliminated, herbivores that depend on these plants suffer. Predators at the top of the desert shrub food chain such as the black-footed ferret also suffer. The black-footed ferret is listed as an endangered species because human development has caused a dramatic decline in the numbers and distribution of prairie dogs which constitute the ferret's primary food source.

- Federal, state, and private predator control programs disrupt the balance between herbivores and carnivores. Poisons indiscriminately kill any scavengers attracted to a poisoned carcass.

Pinon Pine and Juniper Forest Community

The pifion pine and juniper forest community-commonly called "P-X-extends between elevations of 6,000 feet to 7,000 feet, on up to 7,500 feet on warm exposures. This community type is prevalent on the slopes of Split Mountain, Blue Mountain, Douglas Mountain, and Diamond Mountain. The Harpers; Corner Road at Plug Hat picnic area is in the middle of a typical P-J community. Utah juniper forms nearly pure stands at the lower elevations with pihon pine mixing in at the upper end. The elevation range of P-J is apparently deter-mined by temperature. Pihon-juniper is limited at lower elevations by severe cold air inversions common in the winter,as well as heavy clay soils. Low precipitation may be an additional limiting factor. Cold temperatures of long duration seem to be the determining factor of the upper elevation. It may be that the soil freezes earlier and stays frozen too long to allow the trees to absorb enough moisture from the soil to survive. Sagebrush, rabbit brush, mountain mahogany, Indian rice grass, Sandberg bluegrass, and mutton grass are common associated shrubs and grasses. The presence of microbiotic soil (a living soil crust of bacteria, algae, fungi, lichens, and mosses that bind surface soil particles together)and mosses on the soil surface are a sure sign of a pristine juniper and pihon tree community that has not been grazed by livestock.

Mule deer are a common mammal dependent upon the pihon-juniper forest. The montane communities are essential for deer to breed and browse during the summer, but they spend the winter almost exclusively in the pihon-juniper community. Other animals dependent upon the pihon-juniper community are the blue-gray gnatcatcher, pihon jay, plain titmouse, Colorado chipmunk, and pihon mouse.

Pinon jays and Clark's nutcrackers are two dominant birds partly responsible for creating the P-J communities. These birds collect the pine nuts and stash them in the ground to be eaten later. Some of the nuts are not retrieved and sprout, starting a new community.

Threats to Pifion and Juniper Forest Ecosystems:

- Development of pihon-juniper communities for human occupation, agriculture, and energy extraction purposes has reduced the habitat available for animals. Chaining is a method commonly used to open areas up for agricultural purposes.

- Excessive hunting of buck deer, and poaching, produce deer populations that are predominantly made up of does, and can eventually adversely affect the genetic makeup of the herd.

- Predator control, particularly of mountain lion, can cause deer herds to increase to such numbers that they over-browse their habitat and damage vegetation.

- Overgrazing of pihon-juniper communities can suppress native grasses reducing their productivity and changing the community to an unnatural type.

Mountain Shrub Community

To be accurate and somewhat picky, there are two types of mountain shrub communities. The two types are mountain big sagebrush and mixed mountain shrub communities. Their distribution depends upon soil type, aspect (the compass direction the slope faces), and elevation. The elevation dictates the winter temperatures the shrubs must contend with. This is a rather hostile environment. Because they are higher on the mountain the wind usually is blowing, the soil is usually rocky, and the slope fairly steep. This translates into a semi-arid and difficult environment to live in. Plants must stay low to the ground and be stocky, woody, and tough. The west slope of Split Mountain and the Harpers Corner Road, which winds across the plateau of Blue Mountain, contain abundant examples of the mountain shrub community. Escalante Overlook, along the Harpers; Corner Road, is particularly interesting in the unusual variety of shrubs such as manzanita.

Mountain big sagebrush community extends from the upper edge of the pihon pine and juniper forest community to 10,000 feet. The soil is usually well drained, shallow, course textured and rocky. Plants in this community can withstand the lower temperatures and higher winds at these elevations. Mountain big sage brush seldom exceeds four feet in height. On protected, north facing slopes with sufficient soil moisture, aspen will invade, which in turn may be succeeded by shade tolerant conifers.

In association with mountain big sagebrush is rabbit brush, bitter brush, and snowberry. Grasses are usually abundant. Grasses, shrubs, and forbs associated with mountain big sagebrush include bluebunch wheatgrass, thickspike wheatgrass, needle and thread grass, muttongrass, sandberg bluegrass, sheep fescue, mountain low rabbitbrush, arrowleaf balsamroot, and lupine.

The mixed mountain shrub community is found from 7,000 to 8,500 feet. It is typically found on soils with dark-colored surface horizons where roots can grow deep. This community is more diverse on protected slopes where the force of the wind is moderated. Common shrubs include mountain mahogany, service-berry, chokecherry, snowberry, mountain big sage, squawbush, squaw current, and Mormon tea. Common grasses and forbs include needle and thread, mutton grass, junegrass, mountain brome, fescue grasses, arrowleaf balsam root, scarlet gilia, and lupine.

Mountain shrub communities rapidly recycle nutrients into fruits, seeds, and juicy leaves providing animals with an abundance of food. Wildlife inhabiting the mountain shrub community must be adapted to the cold winters or be able to migrate to warmer habitat. Mule deer spend the summers browsing on mountain shrubs and in the winter move down to lower elevations. Mountain mahogany is frequently browsed by deer in winter. The shrubs respond by growing lateral branches and buds. The more heavily the shrubs are browsed the more spiny the branches become, making it more difficult for the deer to browse. This is their defense mechanism against heavy browsing. The yellow-bellied marmot, Nuttal's cottontail, and dwarf shrew are mammals exclusive to these shrublands. Birds such as the lazuli bunting, sage grouse, green-tailed towee, breed almost exclusively in mountain shrublands.

Threats to Mountain Shrub Ecosystems:

- Overgrazing causes the density of sagebrush stands to increase. Because cattle do not find sage-brush palatable, they eat the herbaceous understory and create bare, disturbed soil between sagebrush shrubs. This disturbed soil is eventually invaded by even more sagebrush, causing the stand to become denser.

- In many parts of Utah, such as along the Wasatch Front, the mountain shrub community is rapidly disappearing because of the growth of the human population attracted to living in the mountains. The increasing number of homesites and roads carved into the mountains can disrupt seasonal deer and elk migration routes and the shrub habitat which many wildlife species are adapted to.

Montane Coniferous Community

Mountain mass and elevation induces higher levels of precipitation. An average of 20 inches or more of precipitation falls annually on the top of Blue, Douglas, Split, and Wild mountains. The presence of rock on or near the surface, such as is seen at Canyon Overlook along the Harpers Corner Road, favors coniferous trees. Cracks in the rock below the shallow mountain soil collect and retain moisture from snowmelt. Trees and shrubs work their roots into these cracks to capture the moisture that will sustain them throughout the dry summer.

Douglas fir communities, such as the one at Canyon Overlook, are limited to limestone and other nonquartzitic substrates at elevations of 7,500 to 8,500 feet, on concave slopes of northerly exposure. Curl-leaf mountain mahogany and Oregon grape are common associated plants.

Ponderosa pine communities, such as those found on the crest of Split Mountain or the north slope of Zenobia Peak, seem to prefer temperature conditions similar to, but cooler than, those of pihon-juniper communities. They are best developed in the warmer elevations away from cold air drainage. Ponderosa pines are found at elevations of 7,000 to 8,000 feet. Bitterbrush is a common understory shrub, as are little leaf mountain mahogany, common mountain mahogany, snowberry, and mountain sage. Ponderosas toler-ate aridity well. Trees collect available moisture through a deep taproot (which reaches depths of six feet in sandy soils; 35 feet to 40 feet in fissured rocks) and have long lateral roots. Warmth and lots of sunlight produce vigorous growth, influencing the widely-spaced growth habits of the ponderosa. The open, park-like understory of the ponderosa community is maintained by occasional lightning-started, creeping ground fires. Fires kill seedlings, but the thick bark of mature trees protects them keeping the stands open and decreasing the probability of hot crown fires, which kill mature trees.

In side canyons along the slopes of Split Mountain, Blue Mountain, and the canyons of the Green and Yampa rivers, Douglas fir and ponderosa pines are found far below the elevations they normally inhabit. These vegetative exceptions point out the diversity of environments that the rough topography in Dinosaur National Monument can create. Deep side canyons shade the trees, and in the evenings cool air flows down these canyons, modifying the environment. Seeps, pour-overs where runoff is channeled, and pot holes provide added moisture for the trees. That's the wonder of diversity at Dinosaur. Countless hidden places in the mountains and canyons provide niches where different plants and animals can survive.

Aspen communities, such as the one on the north slope of Stuntz Ridge along the Harpers; Corner Road, can cover extensive northerly exposures from 7,500 to 9,500 feet in elevation. On loamy soils grasses and forbs can form a lush understory.

Douglas fir, ponderosa pine, and aspen were much more common in this area at one time. During the Pleistocene Period (2 million to 10,000 years ago-also known as the Ice Age) the climate was cooler and wetter allowing these trees to grow at far lower elevations. During this time, ponderosa pine and Douglas fir were the most common trees in valleys of the Uinta Basin. The desert shrub and pihon-juniper communities so common in the Uinta Basin today were found far to the south and at lower elevations, where the climate was warmer. Ten thousand years ago the climate began to warm and Pleistocene vegetation was pushed up to the high country. Desert shrub and P-J vegetation invaded the Basin. The Douglas fir, ponderosa pine, and aspen, as well as other plants like Ute ladies tresses (E), and park rock cress, are remnants of the Pleistocene. Are these small montane communities in Dinosaur stable or declining? Only time will tell. If global warming is a reality, these small pockets of greenery may be on their way out. A catastrophic fire, prolonged drought, or massive bark beetle infestation could also doom these communities.

Threats to Montane Coniferous Ecosystems:

• Global warming may eventually eliminate these communities.

• A severe bark beetle infestation can destroy a small Douglas fir or ponderosa pine community.

• Fire suppression can cause ponderosa communities to become unnaturally dense, less productive, and eliminate reproduction. The community continues to mature and eventually the trees die and are replaced by another community type. Fire suppression prevents aspen from colonizing burned over areas. Suppression also allows dead fuel to accumulate on the forest floor increasing the risk of catastrophic crown fires.