Clayey Bottomland 19-26" PZ

Description

The Midgrass/Shortgrass Community (1.1) is an open prairie dominated by mid and shortgrasses. Trees such as hackberry, bumelia and willow grow along the drainage ways. Smartweed and low growing sedges may be found in the common small depressions. Tobosa is the dominant grass with sideoats grama, vine mesquite, and cane or silver bluestem as the dominant midgrasses. Buffalograss and curly mesquite are common shortgrasses. Forbs included mallow, verbena, greenthread and annual forbs. Shrubs are scarce and mesquite may also be present but kept as scattered multi-stemmed shrubs by repeated wildfires.

The Tobosa/Shortgrass Community (1.2) is a tobosa-dominated grassland community being encroached by woody species that previously have been held at low densities by repeated fires and competition from a vigorous grass component. Saline conditions may occur, resulting in increased amounts of alkali sacaton and inland saltgrass. Salt cedar can become invasive on this site. Woody species, including pricklypear and mesquite, increased in density because continuous heavy grazing by livestock reduced grass cover, exposed soil and reduced fine fuel necessary for effective fires.

Submodel

Description

The Tobosa/Shortgrass-Mesquite/Mixed-Brush Community (2.1) presents fifteen to forty percent woody plant cover dominated by mesquite with a tobosa/shortgrass understory. The diversity of the grassland component declines while woody plants and unpalatable forbs increase. All, but the more palatable woody species, have increased in size and density. The typical woody plant cover is mesquite as the dominant overstory with pricklypear, wolfberry, lotebush, ephedra and broomweed as common understory shrubs. Willows, hackberry and mesquite increase along the stream. Tobosa dominates the herbaceous layer in the interspaces between trees and shrubs. Tobosa remains dominant, but as regression progresses under heavy grazing pressure, tobosa gives way to buffalograss and other less palatable shortgrasses and forbs.

The Mesquite/Tobosa/Annuals Community (2.2) is a mesquite-dominated shrubland. Remnants of the reference grassland vegetation, mostly tobosa, shortgrasses, shade tolerant forbs and annuals, occupy the shrub interspaces. The typical woody plant cover is mesquite as the dominant woody species 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 shortgrasses, such as whorled dropseed, white tridens and weedy annuals. Because of grazing pressure and competition for nutrients and water from the woody plants, the grassland component shows lack of plant vigor and productivity.

Submodel