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: At lower elevations blue grama, black grama, and tobosa are the dominant grasses, with sideoats grama, vine mesquite, and plains lovegrass as sub-dominants. At higher elevations, blue grama, sideoats grama, and western wheatgrass dominate, with vine mesquite, plains lovegrass, black grama, and tobosa as sub-dominants. Continuous heavy grazing will cause a decrease in sideoats grama, western wheatgrass, black grama, vine mesquite, and fourwing saltbush. At higher elevations this may result in a community dominated by blue grama. At lower elevations, tobosa and threeawns may dominate. A community of perennial grasses with broom snakeweed as the sub-dominant component may occur in response to overgrazing, or as a result of late fall/early spring moisture following drought. 6 Shrubs and succulents common to the site include yucca, fourwing saltbush, sumac species, juniper, broom snakeweed, and cholla.

Diagnosis: Grass cover is uniform and evenly distributed. Litter cover is high, averaging 25 percent. Shrub/succulent cover is low averaging only 2 percent. Evidence of erosion such as large water flow patterns, rills and gullies are infrequent.

Other grasses which would appear on this site include:
bottlebrush squirreltail, galleta, alkali sacaton, hairy grama, mat muhly, ring muhly, green sprangletop, Hall’s panicum, plains bristlegrass, little bluestem, silver bluestem, Indiangrass, fluffgrass, buffalograss, wolftail, tridens spp., and needle grass.

Other shrubs include:
cholla, juniper, pinyon, creosotebush, oak spp., broom baccharis, pricklypear, Apacheplume, dalea spp., winterfat, and algerita.

Other forbs include:
wooly loco, wooly Indianwheat, cudweed, thistles, annual sunflowers, mullin, wildbuckwheat spp., nightshade spp., milkweed spp., and bladderpod.

State 2
Shrub-Dominated

Community 2.1
Shrub-Dominated

Additional States:

Shrub Dominated: This state is characterized by the predominance of shrubs with perennial grasses as the subordinate component. Grass cover varies inversely with shrub density. Typically juniper and broom snakeweed are the dominant shrubs. Juniper tends to dominate at mid-to upper elevations with blue grama as the subordinate grass component. Broom snakeweed may come to dominate across most elevation ranges with either blue grama or tobosa as the subordinate grass species.

Diagnosis: Shrubs are found at increased densities relative to the Grassland State. Grass cover is variable ranging from fairly uniform to patchy with large connected bare areas present. Blue grama or tobosa are the dominant grasses, and threeawns, ring muhly, cholla and prickly pear typically increase in representation.

Transition to Shrub Dominated State (1a): Seed dispersal of shrubs, loss of grass cover, resource competition between shrubs and grasses, and lack of fire are all believed to facilitate the 12 encroachment of shrubs. Wildlife and livestock (especially birds and sheep) are instrumental in the dispersal of juniper seed. 3, 4 Broom snakeweed produces abundant light seed and the dispersal mechanism is mainly wind.5 Sites that receive above-average late fall/early spring moisture following drought,6 or that have been overgrazed 7may be quickly invaded by broom snakeweed. Drought is detrimental to grasses and the establishment of juniper seedlings, but larger, established trees may gain a competitive edge facilitating juniper dominance. Competition is an important constraint on the establishment of shrub seedlings, because grass roots preempt resources, such as water.2 However, during wet years shrub seedlings may establish in good stands of grass due to reduced moisture competition. Once shrub seedlings become established, and if their roots are capable of extending below this zone, competition for soil moisture declines.2 Overgrazing may facilitate the establishment of shrub seedlings by providing competition free areas, but livestock exclusion alone would not prevent shrub expansion. Historically, periodic fire may have helped to suppress shrubs by completely killing some species, disrupting seed production cycles, and suppressing the establishment of shrub seedlings.1

Key indicators of approach to transition:
* Decrease or change in composition or distribution of grass cover.
* Increase in size and frequency of bare patches.
* Increase in amount of shrub seedlings.

Transition back to Grassland (1b) Brush control is necessary to initiate the transition back to the grassland state. Prescribed grazing will help ensure adequate rest following brush control and will assist in the establishment and maintenance of grass cover. Once the transition back to the Grassland State is achieved, prescribed fire may help in maintaining grass dominance.

State 3
Guillied State

Community 3.1
Guillied State

Gullied State: Loss of grass cover, accelerated erosion, and gully formation characterize this state. Blue grama or tobosa are typically the dominant grasses. Shrub densities reflect either those of the Grassland State or The Shrub-Dominated State, depending on the transition pathway.

Diagnosis: Grass cover is patchy with large bare areas present. Erosion is evident by the presence of water flow patterns, rills and gullies.

Transition to Gullied State (2,3a): Transitions to the Gullied State occur in response to the loss of grass cover, and subsequent erosion. As grass cover is reduced, organic matter, infiltration, and soil surface stability decrease.

Key indicators of approach to transition:
* Reduction in grass cover (on site, or on surrounding uplands).
* Increase in size and frequency of bare patches.
* Presence of litter dams, water flow patterns, rills and gullies.

Transition back to Grassland (3b) Erosion control structures or shaping and filling gullies may help regain natural flow patterns and allow natural revegetation to take place. Prescribed grazing will help ensure proper forage utilization and reduce grass loss due to overgrazing. Brush control will be necessary if from transition (2).