Habitat and Biotic Communities of Hawkins Preserve
Visitors to the Hawkins Preserve readily note that there are several distinct associations involving plants, soil, geology, topography, and wildlife. These associations are also referred to as vegetation communities, plant communities, habitat, phytosociology, or biotypes. Within the preserve seven vegetation communities have been classified, as described below. Collectively they make up a 120 acre natural museum with well over 200 species of plants and wildlife as well as variations in soils, geology and topography. Even though the Hawkins Preserve area has been inhabited or used by humans since prehistoric times, its current protected status gives visitors an excellent opportunity to observe or study the recovery process.
Piñon-Juniper (PJ) Woodland or Pygmy Forest
This prominent community is characterized by the presence of both piñon and juniper trees. In recent years, nearly half of the piñons have been killed due to drought and a bark beetle infestation. The understory consists of sagebrush, prickly pear cactus, grasses (blue grama, sand dropseed, and Indian rice grass), Gambel's oak, Mormon tea, yucca and serviceberry. Soils are made up of wind-deposited sands mixed with abundant organic material. This is overlain with a cryptobiotic crust. This woodland serves as a major habitat for a variety of wildlife including mule deer, squirrels, grey fox, and ground squirrels. This is also the main nesting and feeding area for many bird species.
Sagebrush Steppe
Interspersed with the PJ woodland are the pocket communities dominated by big sagebrush. Since many ecologists believe that this community was originally derived from native grasslands, it is commonly referred to as a sagebrush steppe. The soils in the sage steppe are deep and sandy with very little understory except broom snakeweed and cheatgrass. Some native grasses (galletagrass, sand dropseed, Indian ricegrass, and blue grama) are coming back. There are indications that this community will eventually transition to piñon-juniper as seedlings of these trees become established. The sage steppe is part of the habitat for black-tailed jack rabbits, grey fox, cottontail rabbits, kangaroo rats, deer mice and mule deer.
Slickrock-Pothole
One of the largest communities in the preserve is easily identified by the exposed Dakota Sandstone formation with its characteristic cracks, potholes, and "slickrock" which gives this community its name. Vegetation in this community is limited to the potholes and cracks where detritus, seeds, and sands are deposited by the winds. Some of the more common plants that find a home here are sideoats grama, sand dropseed, prickly pear, hedgehog cactus, and little bluestem. The more stable sites often develop into miniature rock gardens and can support yuccas, piñons, junipers, bitterbrush and goldenaster. The deeper potholes also provide habitat for aquatic wildlife. After a summer rain, look for water beetles, fairy shrimp, mosquito larva, earth worms, and water skimmers.
Rimrock
Paralleling the southern edge of the preserve is a large fracture in the Dakota Sandstone, causing a broken rock formation and 40 ft-high cliffs. Structures within this community include the exposed rim, spillways, large boulders, shaded soil deposits, exposed shale and coal deposits, deep cracks, alcoves, and caves. Some very unique vegetation occurs here including poison ivy, chokecherry, skunkbush, hackberry, singleleaf ash, cottonwood, gooseberry and Gambel's oak. This is also the habitat for several species of lizards, chipmunks, bats, and swallows. Foxes, skunks, and coyotes find this an ideal area for dens.
Alluvial Bottomland
The alluvial bottomland is a former flood plain that lies below the rimrock. It is incised by McElmo Creek and its tributaries. The soils in this alluvial bottomland are deep clays and are highly alkaline. Prior to 1910 this area was considered prime crop land and produced both wheat and alfalfa. Periodic flooding of McElmo Creek has cut deep arroyos, lowered the water table and left a highly unstable, disturbed soil surface. The vegetation reflects these conditions where drought and saline-resistant perennials coexist with many weedy annuals. Characteristic species include greasewood, four-wing saltbush, thistles, seepweed, pepperweed, horehound, tumble mustard, Russian thistle, and salt grass. This area is quite fragile so visitation is highly restricted.
Riparian Corridor and Intermittent Streams (Wetlands)
Although this community consists primarily of McElmo Creek and the current narrow floodplain, the description also applies to intermittent streams, seeps and wetlands found above the rim. There are many birds and mammals that utilize this corridor as part of their habitat. This is also the community that is most severely affected by the invasive saltcedar, also known as tamarisk. Other identifying plants include coyote willow, cottonwood, cat-tail, sedges, rushes, poison ivy, rabbitbrush, salt grass, and common reed.
Post-disturbance and Dunes
This is a catch-all community designation for those areas within the preserve that have a recent history of intense disturbance. Disturbance is caused by excavation of archaeological sites, burning vegetation, dunes, former ranching facilities and activity related to the trails. These sites are often devoid of native plant species and are highly susceptible to erosion. Some of the species that do occur include wolfberry, greasewood, four-wing saltbush, stork's bill, cheatgrass, purslane, and snakeweed.
