Very Shallow 25-28" PZ

Description

The Midgrass/Shortgrass Prairie Plant Community is the reference plant community of the Very Shallow Ecological Site. It is a Midgrass/Shortgrass Prairie Community, dominated by grasses, a large variety of perennial forbs, scattered shrubs and a few trees. This is a somewhat open grassland community, with considerable amounts of bare ground, often with caliche or limestone fragments on the surface. Midgrasses include little bluestem, cane bluestem, sideoats grama and plains bristlegrass. Shortgrasses include curlymesquite, buffalograss, slim tridens, hairy tridens and Texas grama. Some of the major forbs are dotted gayfeather, bushsunflower, catclaw sensitivebriar, halfshrub sundrop, and trailing ratany. The site has less than 10% woody canopy, including low shrubs, such as catclaw, littleleaf sumac, skunkbush, and feather dalea. There are also a few scattered trees such as hackberry and juniper. Opportunistic, ephemeral plants, predominately cool-season species, commonly occupied bare areas following significant rainfall.

Submodel

Description

The Shortgrass/Shrub Community (2.1) is dominated by shortgrasses, including curlymesquite, buffalograss, slim tridens, and Reverchon bristlegrass. Midgrasses, which dominated the reference plant community, are scarce but remnants will remain, due to their resilience, as well as their presence in soil seed banks. The more palatable forbs, such as bushsunflower, purple prairieclover, Engelmann’s daisy, and gaura are replaced by less preferred species, including broom snakeweed, croton, gray coldenia, plains zinnia and silverleaf nightshade. Woody plants with canopy cover of 10-15 % would co-dominate the site. Productivity is much lower than the Grassland State due to loss of the more productive midgrasses and increase of bare ground. The Shortgrass/Shrub Community (2.1) produces only about 800 to 1,000 pounds air-dry biomass per acre.

The Broom snakeweed/Shrub Community (2.2) is dominated by dense stands of broom snakeweed and shortgrasses in the lower herbaceous layer, while shrubs would continue to co-dominate the overstory. Broom snakeweed is a highly competitive perennial forb with a thick woody-like base and perenniating stems. It occurred as a minor component in the reference plant community, but continued to increase in density and weight as the site deteriorated and crossed the threshold from the Grassland State to the Shrubland State. Under the dominance of broom snakeweed, even the shortgrasses are greatly suppressed, leaving only weak pioneer perennials, as the major grasses under these degraded conditions. Very few remnants of midgrasses are present, surviving only in the protection of thorny or spiny shrubs. Annual forbs are more abundant during moist periods. Yucca and cacti are also more abundant. Juniper increases on the site, but remain scattered, rather than forming dense closed canopy as seen on some other degraded sites.

The Shrub/Shortgrass Community (2.3) does not result from the crossing of a threshold to a new vegetative state, but a significantly improved plant community within the Shrubland State. This community represents a more short-lived plant community, co-dominated by woody shrubs and shortgrasses. Shortgrasses, such as curlymesquite, hooded windmillgrass, Reverchon bristlegrass, slim tridens, Hall’s panicum, hairy grama and threeawns species occur in the lower herbaceous layer. Shrubs, such as pricklyash, Texas persimmon, algerita, catclaw acacia, catclaw mimosa, and juniper trees, continue to dominate the overstory, but at reduced densities and canopy cover. Higher production occurs from the shortgrasses and occasional midgrasses, with reduction in competition from broom snakeweed and woody plants. Much of the production is still from shrubs and lower succession grasses and forbs, including annuals. This would represent a management-orientated plant community, so the degree of canopy reduction would vary depending upon resource management objectives.

Submodel