Draw 19-26" PZ

Description

The Midgrass/Tallgrass Savannah State is the reference plant community of the Draw Ecological Site. It is a savannah, with wide open areas dominated by primarily warm-season midgrasses such as little bluestem, sideoats grama, plains bristlegrass, and white tridens, along with a fair representation of tallgrasses such as big bluestem, Indiangrass, and switchgrass. The woody component of this savannah is about 10% intermittent woody canopy from species such as hackberry, western soapberry and occasional liveoak. Occasional honey mesquite also occurs on the site, where it grows into large trees with trunk diameters exceeding 15 inches. This site has a minor component of low growing shrubs such as elbowbush, whitebrush, and bumelia. The plant community also includes a good variety of perennial forbs. Cool-season annual forbs occupy bare areas following late fall or winter precipitation usually completing their life cycle by late spring. Productivity of the Draw Ecological Site is relatively high due to the deep, fertile soils and extra water received as runoff from adjacent sites.

Submodel

Description

The Woodland/Cool-season Grass State is composed of cool-season grasses such as Texas wintergrass and western wheatgrass and has largely replaced the warm-season midgrasses and tallgrasses, which previously dominated the reference plant community. Some of the grasses remaining may include tobosa and alkali sacaton due to their lower palatability and competitive nature, buffalograss, which will tolerate some intermittent shade, silver bluestem, meadow dropseed, and white tridens. The more palatable forbs, such as Maximilian sunflower, Englemann’s daisy, and bushsunflower will be replaced by less preferred forb species, such as western ragweed, silverleaf nightshade, heath aster, and curlycup gumweed. Woody plants will increase strongly to dominate the overstory with total canopy cover approaching 15-20%. Low shrubs will be the first woody plants to increase and invade the community.

Submodel

Description

The Brushland/Woodland Vegetative State (3) is represented by the Mesquite/Juniper Woodland Community (3.1). Honey mesquite and juniper dominate the upper canopy layer of this plant community. This effect will allow the juniper to become a co-dominant woody species along with mesquite in the upper canopy layer of this plant community. The mid layer understory and interspaces among the larger trees are dominated by a wide array of low shrubs, including whitebrush, lotebush, Texas persimmon, pricklyash, catclaw, and agarito. Total woody canopy exceeds 50%. Large amounts of pricklypear and tasajillo occupied more sparse understory and openings among the woody plant. The understory herbaceous layer is dominated primarily by Texas wintergrass. Small openings are occupied primarily by shortgrasses, including red grama, Texas grama, threeawns, tumble windmillgrass, and sand dropseed. Tallgrasses are no longer present and about the only significant amounts of midgrasses include silver bluestem, tobosa, and alkali sacaton. Forbs include western ragweed, heath aster, silverleaf nightshade, sticky selloa, and broom snakeweed (Gutierrezia sarothrae). A few shade-tolerant forbs also occur in the understory. Cool-season annual forbs such as filaree, plantain, tansymustard, pepperweed and bladderpod are prevalent following fall and occasional winter precipitation.

Submodel

Description

The Native Seeded Community (4.1) represents a management-induced vegetative state. This community is the result of artificial revegetation of a degraded natural plant community in an effort to speed vegetative transformation to a native Open Grassland State (4). Vegetative conversion generally is more applicable under conditions where rangeland plant communities have regressed severely, especially in association with heavy brush invasion, such as the Woodland/Cool-season Grass Community (2.1) or the Mesquite/Juniper Woodland Community (3.1). Cropland, deteriorated pastureland, or abandoned cropland also may be converted to the Native Seeded Community.

Adapted native grass mixtures for revegetation of this site include midgrasses, such as sideoats grama, plains bristlegrass, and green sprangletop while tallgrass species might include switchgrass, big bluestem, Indiangrass and Eastern gamagrass (Tripsacum dactyloides). Forbs suitable for seeding this site would include Maximilian sunflower, bundleflower, bush sunflower, and prairieclover. Fourwing saltbush would be a suitable shrub to be included in the range seed mixture. Commercial seed sources of adapted forbs and shrubs generally are scarce. Annual production generally ranges from 2250 to 4500 pounds air-dry biomass per acre. Native grasses can successfully compete with the annual grasses and forbs, which often appear during initial establishment. Native grasses are somewhat slower in establishing viable stands through artificial revegetation, than some of the introduced pasture grasses. However, once established and with proper grazing management, native grasses have greater longevity and sustained productivity without high-level energy inputs.

The Introduced Seeded Community (4.2) is a management-induced vegetative state. It is the result of intensive cultural practices designed to speed the vegetative transformation of a natural plant community, primarily to produce a more economically desired plant community. Seeded pasture usually consists of a monoculture of grasses, such as kleingrass (Panicum coloratum), old-world bluestem (Bothriochloa spp.), or weeping lovegrass (Eragrostis curvula), or a mixture of two or three compatible species. These are generally introduced or improved cultivars, having characteristics desired for forage, erosion control, water conservation, or wildlife habitat.

Submodel