Name:
Sporobolus wrightii Herbaceous Alliance
Reference:
Western Ecology Working Group of...
Description:
Vegetation in this alliance has a moderately dense tall-graminoid layer dominated by tall bunch grasses. A sparse layer of medium-tall grasses may be also be present. Stands of this grassland alliance occur in swales and various lowland sites. Elevation ranges from 1220-1600 m. Slopes are typically flat to gentle with any aspect. Climate is semi-arid with most of the 25-43 cm of annual precipitation falling during the late summer and early fall monsoon period. Precipitation may concentrate in these lowland sites from upland runoff during the typically high-intensity convection storms common during the monsoon season. In four stands of this alliance ground cover ranged from 20-80% bare soil, 20-80% litter, and 3-35% basal vegetation. These soils were derived from clay alluvium and ranged in texture from silty clay loams to clays. This grassland occurs in a variety of sites, from riverbanks, sandy washes and floodplains to upland areas where microtopography or edaphic conditions allowed for accumulation of water. It may also be found in lower salinity sites within depressional wetlands such as bolsons and playas. Typically soils are derived from alluvium and are fine-textured, non-alkaline, and deep with high moisture-holding capacity. The sandy wash sites presumably have coarser substrates. These grasslands often occur on sites that have a high water table or are subject to periodic flooding. Stands of this semi-desert grassland alliance occur in swales and lowlands including riparian zones. These grasslands have a moderate to dense tall-graminoid layer typically dominated by the tall bunchgrass Sporobolus wrightii, with small amounts of mid grasses. The other characteristic grasses may include Panicum obtusum, Panicum hallii, Digitaria californica (= Trichachne californica), Pleuraphis mutica (= Hilaria mutica), Sporobolus airoides, and Bouteloua gracilis. While some stands have moderately high cover of Ambrosia psilostachya, forb cover is generally sparse, but it may be diverse. Scattered shrubs such as Prosopis spp. are not uncommon. Near riparian woodlands, occasionally trees such as Populus fremontii, Fraxinus pennsylvanica, Celtis laevigata var. reticulata (= Celtis reticulata), and Juglans spp. may be present. In several stands of this alliance, the canopy cover of graminoids ranged from 30-70%. Sporobolus wrightii canopy cover ranged from 30-65%. Other common grasses include Panicum obtusum, Muhlenbergia richardsonis, and Eragrostis spp. Common forbs may include Portulaca pilosa, Datura quercifolia (= Datura ferox), Mentzelia pumila, Solanum elaeagnifolium, Amaranthus palmeri, Sphaeralcea hastulata. Occasionally, scattered shrubs, such as Artemisia dracunculus, Chilopsis linearis, or Mimosa aculeaticarpa var. biuncifera, were present. Enhanced soil moisture from the slope position and the high water-holding capacity of the fine-textured soil promotes abundant grass growth. The high grass cover further enhances soil moisture by reducing evaporation from the soil and increasing water infiltration. These conditions promote well-developed soils.
Accession Code:
VB.CC.20597.SPOROBOLUSWRIGH
Plot-observations of this Community Concept:
0
|