Sandy 12-17" PZ

Description

The Tall/Midgrass Community (1.1) is the interpretive or "reference" plant community for the Sandy Ecological Site. Herbivory by migrating bison and indigenous antelope influenced the plant composition and structure, but not as much as frequent and intense wildfires and recurring long droughts, which kept woody species in check. Havard oak motts were widely scattered in protected areas, but probably made up less than ten percent of the plant canopy. Sand sagebrush, broom snakeweed and yucca were also typical, but infrequent, shrubs. Little and sand bluestem along with mesa and giant dropseeds were the dominant or co-dominant grasses throughout the site depending on variations in soils and water relations. Also occurring on the site, but in smaller amounts, were midgrasses cane and silver bluestems, black grama, sideoats grama, plains bristlegrass, and spike dropseed. Common forbs found on the site include prairie clover, dotted gayfeather, wild alfalfa, catclaw sensitivebriar and bundleflower. The Tall-Midgrass Grassland community produced from 1,000 to 2,500 pounds of biomass annually.

The Midgrass/Shrubs Invading Community (1.2) is the result of the interaction of overgrazing, reduction in intensity and frequency of fires and possibly climate change. The reduction in vegetative structure and ground cover resulting from continued overgrazing as well as reduction in fire frequency and intensity allows the shrubs to become established. Havard oak, mesquite, broom snakeweed and sand sagebrush increase in density and cover, varying from 10 to 20 percent ground cover. Sand dropseed, hooded windmillgrass and perennial three-awns begin replacing the more palatable tall and midgrasses found in the reference community. Most forbs such as gaura, groundsels, palofoxia and wild buckwheat persist in the Midgrass/Shrubs Invading Community. Annual yield ranges from 800 to 2,300 pounds.

Submodel

Description

The Mixed Shortgrass/Shrub Community supports a 20 to 45 percent woody canopy cover with mesquite, Havard oak, sand sagebrush, broom snakeweed and yucca the most common shrubs. Havard oak generally dominates on deep fine sand areas and mesquite on loamy fine sand portions. This plant type is the result of selective overgrazing by livestock and the differential response of plants to defoliation over a long period of time. There is a continued decline in diversity of the grassland component and an increase in woody species and unpalatable forbs.

The Shrub/Shortgrass/Annuals Community is the result of many years of overgrazing, lack of periodic fires and little brush management. Havard oak and mesquite dominate the Shrub/Shortgrass/Annuals Community, which is essentially a dense shrubland. Under extreme conditions of overgrazing and drought, the site deteriorates to active dunes and blowouts. Common understory shrubs are broom snakeweed, yucca and sand sagebrush. With continued heavy grazing and no brush control, the shrubs can approach 70 percent or more ground cover. Short-grasses and low quality annual and perennial forbs occupy the woody plant interspaces.

Submodel