Ecological dynamics

Loamy Upland, Limy, 12"-16" p.z. ecological site is dominated by warm season perennial grasses. All the major perennial grass species on the site are well dispersed throughout the plant community. Perennial forbs and a few species of low shrubs are well represented on the site. The aspect is open grassland. With continuous heavy grazing, palatable perennial grasses like black grama and sideoats grama and plains lovegrass decrease. Increasers under such circumstances include curly mesquite, fluffgrass, threeawns and, in places, false mesquite. With severe deterioration, shrubby species increase to dominate. Loss of porous surface soil causes a reduction in the site's ability to effectively use intense summer rainfall. Natural fire was important in the development of the climax plant community. Stable areas of the site can produce effective herbaceous covers with up to 10% canopy cover of mesquite. In areas where half-shrubs dominate the under-story, the potential production of perennial grass is about the same as the present production of half-shrubs once they are removed from the plant community by fire or brush management.

Catclaw, white-thorn acacia and wait-a-bit mimosa increase in the absence of fire for long periods of time. Native perennial grasses maintain dominance with good grazing management, and with shrub canopy levels less than 5%. Short gramas, fluffgrass and curly mesquite are dominant and the site remains stable as long as their basal cover does not drop below 6 or 7%. Snakeweed and burroweed cycle with climate but never gain dominance. Cholla and prickly pear cycle with climate but never become dominant. Some soil compaction has occurred due to livestock traffic, but hydrologic relationships are not impaired.

Mesquite has increased in the absence of fire for long periods of time to canopy levels of 10%. Lehmann and / or Boer lovegrass have invaded from seeded areas and dominate the under-story. Remnant native perennial grasses diminish over time. Fire may act to increase exotic lovegrass at the expense of native perennial grasses, but may allow native annual species a chance to make seed and persist in the seed-bank. Some soil compaction has occurred due to livestock traffic, but hydrologic relationships have not been impaired.

Mesquite and other large shrubs have increased and are dominant with canopies from 10 to 15%. Native and non-native annual forbs and grasses, both cool and warm season, dominate the understory. Snakeweed and burroweed cycle with climate, but both remain important in the plant community. Native perennial grasses are largely gone, due to the interactions of drought, fire and continuous, heavy grazing. Usually, soil compaction and the loss of herbaceous cover have resulted in sheet and rill erosion on this site. Hydrologic relationships have changed to increase the amount of runoff. As the, coarse textured, soil surface is lost to erosion, the ratio of runoff to infiltration increases.

Mesquite continues to increase up to canopy levels of 25%. Other shrubs and succulents dominate the under-story. Remnant perennial grasses exist only in the protection of cacti and shrubs. Occasional fires may burn in exceptionally wet seasons, but well established mesquite and other shrubs sprout back to a thorn scrub stage. Soil compaction, due to heavy livestock traffic, and lack of herbaceous cover has resulted in sheet, rill and gully erosion. Hydrologic relationships have changed to greatly increase the amount of runoff. As the, coarse textured, soil surface is lost to erosion, the site loses its ability to capture intense summer rainfall, productivity declines, and cool season shrubs and succulents are the only plants able to persist.

Treated/Managed grassland communities are a man made pasture after brush management practices (either chemical or mechanical). The grassland community will either be native perennial grass dominant or, more likely, an introduced African lovegrass monoculture. The grassland community can be created from either of the shrub dominated states. Mesquite and other shrubs are bulldozed; brush is placed in gullies and rills; and perennial grasses are seeded, as necessary. If any non-native lovegrasses are present in the community, they will explode. With good grazing management, hydrologic relationships are good and productivity remains high. Root plowed areas typically eliminate any runoff for long periods of time (25 to 30 years), depending on grazing management. Mesquite and other shrubs will reinvade these areas and maintenance treatments (every 15 years) of herbicides, fire or mechanical methods will be needed to maintain a grassland aspect.