Clayey Bottomland 23-30" PZ

Description

The Mixed-Grass Prairie Community is an open prairie dominated by mid and shortgrasses. Trees such as hackberry, western soapberry and American elm grew along the drainage ways. The plant community provided good ground cover and protection from erosion during infrequent flooding events. Smartweed and low growing sedges were found in the small depressions made by old drainages. Tobosa was the dominant grass in the drier western portion of the MLRA with sideoats grama, vine mesquite, and cane or silver bluestem, Arizona cottontop and white tridens common midgrasses throughout. Buffalograss and blue grama were common shortgrasses. Texas wintergrass and western wheatgrass were important parts of the cool-season grass component. Alkali sacaton was common where soil salt accumulations were high. Reference community forbs included western ragweed, heath aster, gaura, verbena, and annual forbs. Reference community shrubs were scarce but probably included fire resistant species such as wolfberry, ephedra, greenbriar and lotebush. Mesquite was probably also present but kept as scattered multi-stemmed shrubs by repeated wildfires.

The Shortgrass Community (1.2) is a shortgrass dominated grassland community being invaded by woody species that previously have been held at low densities by repeated fires, infrequent droughts and competition from a vigorous grass component. Woody species, including pricklypear and mesquite, increased in density wherever continuous heavy grazing reduced grass cover, exposed soil and reduced fine fuel necessary for effective fires. Tobosa and buffalograss become dominant where they were present originally. Blue grama, white tridens, alkali sacaton, vine mesquite, and the feathery bluestems persist in this vegetation type. Texas wintergrass may increase on some areas, especially in and around woody plants, in response to shading or possibly climate change toward more cool-season precipitation. Western wheatgrass generally declines with overgrazing. Most of the perennial forbs found in the reference community remain in this plant community, although in lesser amounts. Saline conditions may occur in overgrazed areas, resulting in increased amounts of alkali sacaton. Salt cedar can become invasive on this site.

Submodel

Description

The Shortgrass/Mixed-brush Community (2.1) supports a 15 to 40 percent woody plant cover dominated by mesquite with a shortgrass herbaceous layer. All, but the more palatable woody species, have increased in size and density. The typical woody plant cover is mesquite dominated with pricklypear, wolfberry, lotebush, ephedra and broomweed as common understory shrubs. Western soapberry, hackberry and mesquite increase along the stream edge. Tobosa dominates the herbaceous layer in the interspaces between trees and shrubs in the western portion of the MLRA where it was present originally. Buffalograss becomes dominant elsewhere. Remnants of grasses and forbs and less palatable species such as alkali sacaton, vine-mesquite, meadow dropseed, threeawn, silver bluestem, white tridens and annuals occur in the woody plant interspaces.

The Mixed-brush/Shortgrass/Annuals Community is a mesquite-dominated shrubland with tree species along the stream line. Remnants of the climax grassland vegetation, mostly tobosa and/or buffalograss, cool season grasses and annuals, occupy the shrub interspaces. The woody plant cover is dominated by mesquite with pricklypear, tasajillo, lotebush and wolfberry common understory shrubs. Tobosa remains dominant in the herbaceous layer initially, but with heavy continuous grazing gives way to buffalograss and other less palatable grasses, such as threeawn, meadow dropseed, white tridens, bristlegrass and weedy annuals.

Submodel