State 1
Reference State

This state represents the most ecologically stable conditions in terms of resistance to erosion. Moreover, this state has the highest potential for productivity and plant diversity.

Community 1.1
Reference Plant Community

Grassland: Sideoats grama, blue grama, western wheatgrass, and vine mesquite are the dominant grasses at mid to higher elevations, with tobosa, blue grama, and vine mesquite dominant at lower to mid-elevations. Alkali sacaton, giant sacaton, silver and cane bluestem are also present across the range of elevations as sub-dominants in the historic community. Some of the shrubs characteristic of this site include sumac species, juniper species, Apache plume, fourwing saltbush, yucca, and catclaw acacia. Typically shrubs are confined to the margins of the swale. Under continuous heavy grazing, there will typically be a decrease in sideoats grama, western wheatgrass, vine mesquite, and fourwing saltbush. Blue grama can increase and become dominant at higher elevations, and tobosa may dominate at lower elevations. Threeawns, dropseeds, and mat muhly will also increase with heavy grazing. Transitions to a Grass/Shrub-Mix may occur in response to a lack of fire, or dispersal and successful establishment of shrub seed. Flood events and loss of grass cover can increase erosion and facilitate the transition to a gullied state. Diagnosis: Grass cover is uniform and evenly distributed. Sideoats grama, western wheatgrass, blue grama, or tobosa are the dominant grasses. Grass and litter cover are high and litter movement is limited to smaller size class litter and short distances (<1m), except following flood events. Shrub canopy cover is low averaging less than 5 percent. Other grasses, which would appear on this site, include: plains bristlegrass, green sprangletop, big bluestem, Indiangrass, switchgrass, Canadian wildrye, plains lovegrass, bottlebrush squirreltail, and wolftail. Other shrubs include: broom baccharis, desert willow, winterfat, tarbush, broom snakeweed, sumac spp., and juniper. Other forbs include: desert holly, blanket flower, threadleaf groundsel, cudweed, and mullin.

State 2
Grass/Shrub-Mix

Community 2.1
Grass/Shrub-Mix

Additional States: Grass/Shrub-mix: This state is characterized by the notable increase of shrubs relative to the grassland state, especially juniper, littleleaf sumac, or Apacheplume. However, grasses remain dominant. Shrubs are no longer confined to the margins of the swale, instead tending to occur in motts scattered throughout the site. Sideoats grama-blue grama-juniper communities occur at mid to higher elevations, and tobosa- littleleaf sumac, and blue grama-Apache plume communities are more typical of lower to mid elevations. Grass cover on swale sites may remain relatively high for extended periods when associated with light to moderate densities of littleleaf sumac, Apache plume, or juniper species. Diagnosis: Shrubs are found at increased densities relative to the grassland state, especially juniper, littleleaf sumac, or Apacheplume. Grass cover is variable, ranging from uniformly distributed to patchy. Typically sideoats grama, blue grama or tobosa remain as the dominant grass species. Transition to Grass/Shrub-mix (1a) Fire suppression and seed dispersal are believed to facilitate the increase and encroachment of shrubs on Swale sites. Historically, fire may have kept shrubs in check by completely killing some species, disrupting seed production cycles, and/or suppressing the establishment of shrub seedlings.1 Wildlife (especially birds) are instrumental in the dispersal of littleleaf sumac and juniper seeds.2, 4 Apacheplume produces abundant feathery seed and the dispersal mechanism is mainly wind.3 Key indicators of approach to transition: Indicators are limited as transitions occur slowly over time and may only require seed dispersal mechanisms. Decrease or change in distribution or composition of grass cover. Increase in amount of shrub seedlings. Transition back to Grassland (1b) Brush control is necessary to initiate the transition back to the grassland state. Possibly, the reintroduction of fire as a management tool may assist in the transition back to the Grassland state, if adequate fuel loads remain. The effectiveness of fire varies by species. Oneseed juniper is susceptible to fire and generally considered a non-sprouting species. Alligator juniper, Pinchot juniper, littleleaf sumac, and Apache plume are reported to be tolerant of fire due to their ability to root sprout and may recover or increase following fire. Prescribed grazing will help ensure adequate rest following brush control and will assist in the establishment and maintenance of grass cover.

State 3
Gullied State

Community 3.1
Gullied State

Gullied State: Loss of grass cover, accelerated erosion, and gully formation characterize this state. Sideoats grama, blue grama, or tobosa are the dominant grass species. Shrub densities are the same as in the Grassland state if the transition is caused by major flood events. If the transition was from the Grass/Shrub-Mix to the Gullied state, then shrubs are found at increased densities, especially juniper, littleleaf sumac, or Apacheplume. Diagnosis: Grass cover is typically patchy with large bare areas present. Erosion is evident by the presence of water flow patterns, litter dams, rills, and gullies. Transition to Gullied State (2a,3) Transitions to the gullied state may occur in response to flood events, and/or loss of grass cover (on or off site), and subsequent erosion. As grass cover decreases, organic matter and surface soil stability decrease. 5,6 Erosion may occur due to increased water flow volume and rate, alongside decreased soil surface stability, and reduced infiltration. Key indicators of approach to transition: Reduction in grass cover (on site, or on surrounding uplands) and increase in size and frequency of bare patches.