Shallow 19-26" PZ

Description

The Midgrass Prairie Community (1.1) is the interpretive or "reference" plant community for the Shallow Ecological Site. Sideoats grama is the dominant or co-dominant grass throughout the site. Big bluestem, little bluestem and Indiangrass occupy favorable micro-sites and were locally dominant. Also occurring on the site, but in smaller amounts, are cane and silver bluestems, Arizona cottontop, Texas wintergrass, Texas cupgrass, vine mesquite and a number of shortgrasses. Live oak and hackberry trees are widely scattered in protected areas, but probably made up less than two percent of the plant canopy. Liveoak tends to decrease moving north through the site. Sumacs, elbowbush, ephedra, bumelia, lotebush, agarito and catclaw are typical, but infrequent, shrubs. Common forbs found on the site include awnless bushsunflower, Engelmann’s daisy, orange zexmenia, prairie clover, dotted gayfeather and bundleflower. The Midgrass Prairie Community produces from 1,500 to 3,000 pounds of biomass annually, depending upon the amount of precipitation. Grasses produced as much as 85 percent of the annual production.

The Midgrass-Shortgrass Community (1.2) is the result of overgrazing by livestock over a long period of time. It is midgrass-shortgrass dominated grassland being encroached by indigenous or invading woody species that had been held at low densities by repeated fires and competition from a vigorous grass component. The preferred tall grasses and midgrasses are being replaced by the more grazing resistant midgrasses and shortgrasses. Numerous brushy species, including juniper and mesquite, are encroaching because overgrazing by livestock has reduced grass cover, exposed more soil and reduced fine fuel for fire. In this plant community type, the increasing woody species are generally less than three feet tall and still subject to control by fire and improved grazing management. The woody canopy varies between 5 and 15 percent depending on severity of grazing, time since burned and availability of invading species. Important grasses are sideoats grama, little bluestem, vine mesquite, cane or silver bluestem, Texas cupgrass, Arizona cottontop, Texas wintergrass and Canada wildrye. Most of the climax perennial forbs persist. Annual primary production ranges from 1500 to 3000 pounds per acre.

Submodel

Description

The Shortgrass/Mixed-Brush Community (2.1) presents a 20 percent or greater woody canopy of Mixed-Brush, including mesquite, juniper and rarely live oak, as the dominant species. There is a continued decline in diversity of the grassland component and an increase in woody species and unpalatable forbs. Sideoats grama is replaced by increases in buffalograss and Texas wintergrass. Remnants of other climax grasses and forbs and unpalatable invaders occupy the interspaces between trees and shrubs. Cool-season grasses such as Texas wintergrass, plus other grazing resistant species, can be found under and around woody plants. Annual primary production is approximately 1000 to 2500 pounds per acre.

The Mixed-Brush/Shortgrass Shrubland Community (2.2) is the result of many years of overgrazing, lack of periodic fires and little brush management. Mesquite and/or juniper dominate the Mixed-Brush/Shortgrass Shrubland Community, which is essentially a dense shrubland state. Trees and shrubs can approach 70 percent ground cover. Shortgrasses and low quality annual and perennial forbs occupy the woody plant interspaces. Characteristic grasses are curlymesquite, buffalograss, hairy tridens, Texas grama, and fall witchgrass. Texas wintergrass and cool season annuals are found in and around tree/shrub cover. Grasses and forbs make up 25 percent or less of the annual herbage production.

Submodel