State 1
Historic Climax Plant Community

Community 1.1
Historic Climax Plant Community

Grassland: The historic plant community is dominated by black, and blue grama. Black grama densities tend to be highest on soils with sandy loam surface textures, and blue grama on soils with loam surface textures. Bush muhly, hairy grama, plains bristlegrass, and sand dropseed also occur in significant amounts. Yucca, winterfat, and ephedra species are the dominant shrubs of the historic community. Fourwing saltbush, creosotebush, tarbush, and broom snakeweed typically occur as sub-dominants. Threadleaf groundsel, wooly groundsel, Leatherweed croton, and bladderpod are forbs commonly found across the site. Extended periods of drought, or drought in combination with heavy grazing can cause a decrease in plants such as black grama, blue grama, bush muhly, vine mesquite, Arizona cottontop, winterfat, and fourwing saltbush. Dropseeds and threeawns may increase in representation and become co-dominant to black or blue grama. Dropseeds and threeawns produce ample viable seed and are not as palatable as either black or blue grama, especially during the dormant season. Threeawns can take advantage of early spring, as well as summer moisture, enabling it to quickly establish following drought. Creosotebush, tarbush, broom snakeweed, fluffgrass and burrograss increase with further site degradation. This increase in shrubs and associated loss of grass cover, perhaps in conjunction with decreased fire frequency may result in a shrub-dominated state. Diagnosis: Black grama and blue grama are the dominant grasses. Grass cover is uniformly distributed with few large bare areas. Yucca, winterfat, and ephedra species are the dominant shrubs. Fourwing saltbush is present.

State 2
Shrub Dominated

Community 2.1
Shrub Dominated

This state is characterized by an increase in shrubs and a decrease in grass cover. Creosotebush, tarbush, and broom snakeweed are the dominant shrubs. Dropseeds, threeawns or bush muhly are the dominant grasses. Retrogression within this state is characterized by a continued reduction in grass cover and an increase in the size and frequency of bare patches. Under heavy grazing pressure grass cover is higher in shrub interspaces when dropseeds or threeawns are the dominant grass, as opposed to bush muhly, whose cover tends to be higher under shrub canopies. This may be due to the forage value of bush muhly, low resistance to grazing, and its ability to successfully establish under creosotebush and tarbush.4 Diagnosis: Shrubs are found at increased densities relative to the grassland state, especially creosotebush, tarbush, and broom snakeweed. Grass cover is patchy with large (>2m) connected bare areas present. Black grama may or may not be present. Wind erosion is common and evidenced by pedestaling of plants and rocks in shrub interspaces. Transition to Shrub-Dominated (1a) Overgrazing and/or extended periods of drought, and suppression of natural fire regimes are thought to cause this transition. Decreases in grass cover give a competitive advantage to shrubs and shrub seedling establishment. Shrubs are better equipped to withstand prolonged periods of drought due to the ability of their root systems to extract water from a larger area than grasses. If periodic fire played a role in naturally suppressing shrubs (especially creosotebush and tarbush), then decreased fire frequency may facilitate this transition. Key indicators of approach to transition: Increase in amount of dropseeds or threeawns Decrease or loss of winterfat and fourwing saltbush. Increase in size and frequency of bare patches. Transition back to Grassland (1b) Brush control is necessary to re-establish grass dominance. Prescribed grazing will help to ensure proper forage utilization following brush control and sustain grass cover. Periodic use of prescribed fire may help in maintaining the grassland state.

State 3
Shrubland

Community 3.1
Shrubland

Shrubland State: This state is characterized by very little grass cover, extensive dominance of shrubs, and accelerated erosion. Creosotebush is typically the dominant shrub, and tarbush often occurs as a sub-dominant. Herbaceous cover is very limited, often restricted to a sparse cover of fluffgrass or annual forbs and grasses scattered across the shrub interspaces, or scattered bush muhly in shrub bases. Diagnosis: Grass cover very sparse or absent in shrub interspaces. Fluffgrass or annuals may be the dominant herbaceous species. Erosion is evident by soil sealing, water flow patterns, pedestals or terracettes. Sub-surface soil horizons may be exposed. Transition to Shrubland State (2) Persistent loss of grass cover, associated erosion, and increased competition for resources by shrubs may cause a transition to a shrubland state. As grass cover diminishes, perhaps due to excessive grazing followed by drought, erosion rates increase. Erosion removes or re-distributes organic matter and available nutrients. As organic matter is lost, soil surfaces seal, reducing infiltration and available water. The relocation of resources from interspaces to shrub bases further increases shrubs competitive advantage. Key indicators of approach to transition: Increase in size and frequency of bare patches. Loss of grass cover in shrub interspaces. Increased signs of erosion—evidenced by pedestalling of plants, soil deposition on leeward side of plants, exposure of subsoil.2 Transition back to Grassland (3) Brush control will be necessary to overcome competition between shrubs and grass seedlings. Seeding may expedite recovery or may be necessary if an adequate seed source is no longer remaining. Prescribed grazing will help ensure adequate deferment and proper forage utilization following grass establishment. The degree to which this site is capable of recovery and benefits derived depends on the cost of restoration, extent of degradation to soil resources, and adequate rainfall necessary to establish grasses. 3 Depending on the extend of soil degradation, the length of time involved for a transition back to the Grassland state may take longer than the typical management timeframe.