Very Shallow Clay 19-26" PZ

Description

The Midgrass/Shortgrass Prairie Community (1.1) is composed of shrubs that were widely scattered in protected areas and along draws, but made up less than one percent of the total annual production. Sideoats grama is the dominant grass throughout the site. Also occurring on the site, but in smaller amounts, were meadow dropseed, silver bluestem, alkali sacaton and a number of shortgrasses. Characteristic forbs are catclaw sensitivebriar, plains blackfoot daisy, western ragweed, dotted gayfeather and Indian rushpea. Lotebush, four-winged saltbush and pricklypear are common woody plants. The Midgrass/Shortgrass Prairie Community produces from 400 to 1200 pounds of biomass annually, depending upon the amount of precipitation. Grasses made up to 90 to 95 percent of species composition and production.

The Shortgrass/Midgrass/Shrub Community (1.2) is composed of less palatable grasses, such as silver bluestem and sand dropseed, and less palatable forbs such as gaura, dotted gayfeather and western ragweed which are replacing the dominants of the reference community. The dominant grasses, such as sideoats grama, meadow dropseed and alkali sacaton, remain, however. Woody species, especially juniper, mesquite, pricklypear, tasajillo and lotebush, are encroaching but are not seriously impacting forage production. Invading brushy species are generally less than four feet tall and provide less than 15 percent canopy.

Submodel

Description

The Shortgrass/Mixed-brush Community (2.1) on the Very Shallow clay site ranges from 15 to 25 percent woody plant canopy of mixed-brush, depending on how long the site has been in the Shrubland State. There is a continued decline in diversity of the grassland component and an increase in woody species and unpalatable forbs. All, except the more palatable woody species, have increased in size. Mesquite is dominant on the site throughout the MLRA. Juniper has spread considerably in recent years. Many of the climax shrubs are present. Typically, agarito, pricklypear, and lotebush form mixed-brush complexes with mesquite and juniper. Remnants of climax grasses and forbs and unpalatable invaders occupy the interspaces between trees and shrubs. As further regression occurs, sideoats grama is replaced with buffalograss.

The Mixed-brush/Shortgrass/Annuals Community (2.2) occurs when the Very Shallow Clay site is overgrazed for many years, fires are excluded, and woody plants are not controlled. With continued overgrazing, the site becomes a shrubland with its interstitial areas occupied by a degraded herbaceous community of shortgrasses and annuals. The shrub canopy acts to intercept rainfall and increase evapotranspiration losses, creating a more xeric microclimate. Juniper and/or mesquite dominate the Mixed-brush/Shortgrass/Annuals Community (2.2). The trees and shrubs can approach 50 percent ground cover. Common understory shrubs are pricklypear, agarita, lotebush, wolfberry, and tasajillo. Shortgrasses and low quality annual and perennial forbs occupy the woody plant interspaces. Characteristic grasses are buffalograss, rough tridens, threeawns, sand muhly, Texas grama and red grama.

Submodel