State 1
Historic Climax Plant Community

Community 1.1
Historic Climax Plant Community

Figure 4. Shrubland

State Containing Historic Climax Plant Community Black grama-dominated state: The historic plant community is believed to have been dominated by black grama, bush muhly, threeawns, burrograss (Scleropogon brevifolius) and sand dropseed (Sporobolus cryptandrus). Annuals are especially dominant at certain times depending on rainfall. Creosotebush, mormon tea (Ephedra spp.), and tarbush are present. Grazing-induced change from this community would be characterized by a reduction in the cover of black grama, bush muhly and dropseeds, and an increase in the proportional representation of threeawns, fluffgrass, shrubs, and annuals. Diagnosis: Black grama is dominant and the density of shrubs is low. Evidence of erosion is infrequent. Transition to threeawn-fluffgrass state (1a): The cause of this transition is presumably due to poor grazing management or other soil disturbance, possibly in combination with drought. Erosion and degradation of the A horizon may reduce the ability of black grama and bush muhly to establish and spread. Transition to shrub-dominated state (2a): The cause of this transition is presumably due to poor grazing management that reduces competition of grasses with shrubs, climate change, or perhaps reduced fire frequencies. Key indicators of approach to transitions: Increases in bare ground, decreases in black grama and bush muhly cover, possibly increased germination of creosotebush (2a).

State 2
Threeawn-Fluffgrass

Community 2.1
Threeawn-Fluffgrass

Additional States: Threeawn-fluffgrass state: Threeawns, fluffgrass, and annuals dominate in this state. Overall herbaceous cover is low and shrubs are not abundant. It is not understood why shrubs do not come to dominate within this state. Black grama may be eliminated and bush muhly may occur at the bases of shrubs. Diagnosis: Bare ground is interconnected, and threeawn and other grass cover is patchy or scattered. Fluffgrass may be abundant. Shrubs are present, but are not dominant. Evidence of erosion, including gullies, rills, pedestalling, and water flow patterns may be apparent. Transition to shrub-dominated state (3a): This may occur if shrub densities increase following the loss of dominant perennial grasses, perhaps due to favorable rainfall patterns. Key indicators of approach to transitions: Increased germination of creosotebush. Transition to shrubland/annuals state (5a): The remaining grass patches are lost due to drought and/or disturbance to grasses by grazing or off-road vehicle use. It is possible that most cases of threeawn-fluffgrass states eventually degrade to annual states due to soil burial of grasses, which is caused by wind erosion from large bare patches, in addition to erosion at grass edges. Key indicators of approach to transitions: Increases in bare ground, evidence of erosion around grass patches and plants (pedestalling), decadence of remaining grasses, decreases in grass cover. Transition to black grama-dominated state (1b): This might be achieved by nutrient amendments to the soil and/or seeding during periods of above-average summer rainfall. Deferred grazing would probably be necessary.

State 3
Shrub-Dominated

Community 3.1
Shrub-Dominated

Shrub-dominated state: This state is characterized by the persistent dominance of creosotebush and other shrubs, including mesquite (Prosopis glandulosa). Threeawns may be the grass dominants and black grama and bush muhly are present in some patches. Fluffgrass may be an important component. Diagnosis: Creosotebush, tarbush, and mesquite are dominant and grass occurrence is patchy. Evidence of erosion, including gullies and rills, are apparent in bare areas. Transition to shrubland/annual state (4): As for 5a above, except that shrubs persist as the sole perennial dominants. Key indicators of approach to transitions: Increases in bare ground, evidence of erosion around grass patches and plants (pedestalling), decadence of grasses, decreases in grass cover. Transition to black grama-dominated state (2b): If competition with shrubs for water and/or nutrients reduces grass dominance in many patches, then shrub control may facilitate black grama and bush muhly reestablishment and vegetative growth. If climatic conditions are not suitable for grass growth then such treatments will be ineffective. Transition to threeawn-fluffgrass state (3b): Shrub removal may not result in recovery of black grama or bush muhly if moderate soil degradation has occurred, or if seeds of these species are not present. Instead, threeawns may proliferate or simply become the default dominants without increasing in cover.

State 4
Shrubland / Annuals

Community 4.1
Shrubland / Annuals

Shrubland/annuals: Shrubs, especially creosotebush, are dominant perennials and annuals may be periodically abundant. In other cases, shrubs are not abundant. Grasses are rare or absent. Erosion is severe. Diagnosis: Perennial grasses are rare, shrubs may be the sole perennial cover. Evidence of erosion, especially pedestalling of shrubs and gullies, is apparent throughout the site. Transition to black-grama-dominated state (6): Shrub removal, the placement of physical structures to collect water or retard erosion, and/or nutrient amendments and seeding may result in recovery of perennial grasses over a period of decades or more. It is possible that only threeawns would recover, in which case the site would recover to the threeawn-fluffgrass state. Data and information sources and theoretical background: Communities and states are derived largely from Jim Powell, NRCS, retired and infrequent observations by Brandon Bestelmeyer, USDA-ARS Jornada Experimental Range.