State 1
Historic Climax Plant Community 1

Community 1.1
Historic Climax Plant Community 1

The Arroyo/Floodplain type consists of two separate elements, the arroyo channel and its associated floodplain. This site is an ephemeral stream floodplain with a gently sloping surface, broad enough that the channel covers only a part of the surface. Vegetation on the site varies dynamically with parent material, distance away from the channel, and amount of gravel and cobble in the soil profile. Trees and shrubs are typically dominant along the channel border, but grasses dominate the floodplain. A wide variety of woody species can occur on this site including, Apache plume, brickellbush, desert willow, mesquite, catclaw mimosa, viscid acacia, and New Mexico walnut. Dominant grass species tend to vary somewhat moving East to West across the resource unit. Cane bluestem and silver bluestem are typical dominants on the western side of the resource unit. Alkali sacaton and giant sacaton tend to dominate more on the eastern side. Other important grasses common to both areas include vine mesquite, sideoats grama, tobosa, Arizona cottontop, and twoflower trichloris. Total annual production on this site is high averaging up to 3500 pounds per acre during years with favorable rainfall. Overgrazing may cause an increase in tobosa, and a decrease in vine mesquite, sideoats grams, Arizona cottontop, and twoflower trichloris. Diagnosis: Trees and shrubs tend to dominate along the channel border, with patches of grass supported by silt accumulation around cobbles, stones, shrubs and trees. Across the floodplain, bluestems, or alkali sacaton and giant sacaton are typically the dominant grasses. Grass and litter cover is high. Trees and shrubs are infrequent and scattered. Bare patches are small, typically less than 1-2 meters across

State 2
Tobosa Grassland

Community 2.1
Tobosa Grassland

Additional States: Tobosa Grassland: This state is characterized by decreased available soil moisture and the dominance of tobosa. Burrograss is typically a component of this state and depending on the degree of soil moisture loss, may become sub-dominant to tobosa. Diagnosis: Grass cover is variable ranging from uniform and continuous to patchy, with increased bare areas. Tobosa is the dominant grass. Tall grasses such as giant sacaton, and bluestems may occur in small patches occupying small, moister micro-sites, or are absent. Burrograss is found at increased densities relative to the HCPC. Shrubs are infrequent and scattered. Transition to the Tobosa Grassland (1a): Decreased available soil moisture due to deepening of the channel may cause the loss of more mesic grasses such as bluestems, giant sacaton, and alkali sacaton, resulting in a tobosa-dominated grassland. Key indicators of approach to transition: Indicators prior to this transition are few and not readily observable. By the time changes in the channel width or steepness or height of channel banks is observable the transition has already begun. Decreases in overall grass heights throughout the water shed. Increases in sediment loading. Transition back to HCPC Grassland (1b) The natural hydrology of the site must be restored to enable the transition back to the HCPC Grassland. Filling or reshaping of the channel may help to restore natural overland flow patterns on to the floodplain, providing the additional run-on water necessary for the establishment and survival of the more mesic grass species.

State 3
Burrograss Grassland

Community 3.1
Burrograss Grassland

Burrograss Grassland: This state is characterized by the dominance of burrograss and increased soil surface sealing. Burrograss favors calcareous fine textured soils and spreads by seed and stolons. It produces large amounts of seed with wiry awns that help in dissemination, and in auguring the hardened callus (tip of the seed) into the soil. The ability of burrograss to auger into soils enables it to establish and expand on bare soils prone to crust over with physical and biological crusts. Diagnosis: Grass cover is patchy with large bare areas present. Burrograss is the dominant grass species. Tobosa may be present in scattered patches. Soil surface sealing is evident on most of the exposed bare ground. Erosion is apparent by the presence of water flow patterns, rills, litter dams, and pedestalling of plants. Transition to the Burrograss Grassland (2a) Loss of deep-rooted grasses and overall grass cover due to overgrazing or extended periods of drought may initiate this transition. As grass cover declines, resistance to water flow decreases and erosion increases, causing surface soils to seal. As surface soils seal, infiltration and permeability decrease. This transition may be soil determined. 3 Key indicators of approach to transition: Decrease in cover of tobosa. Increased amount of bare ground. Increased evidence of physical and biological crusts. Transition back to Tobosa Grassland (2b) Erosion control structures or shaping and filling gullies may help regain natural flow patterns and establish vegetation if the flow has been channeled. Prescribed grazing will help establish proper forage utilization and maintain grass cover and litter necessary to protect the site from accelerated erosion.

State 4
Shrub-Dominated

Community 4.1
Shrub-Dominated

Shrub Dominated: Increased cover of shrubs characterizes this state. Mesquite, catclaw mimosa, viscid acacia or creosotebush are typically the dominant shrub species. Grass cover is typically patchy with large bare areas present, however in some instances grass cover may remain relatively high for extended periods when associated with light to moderate infestations of mesquite, catclaw mimosa, or viscid acacia. Variations in soil characteristics may determine which shrub species increase. Mesquite is well adapted to a wide range of soil types, but increases more often on draw sites that exhibit fine textured, deep soils low in carbonates. Catclaw mimosa and viscid acacia prefer gravelly soils and tend to form thickets along the edges of the channel. Creosotebush is less tolerant of fine textured soils, perhaps due to its high oxygen demand, and tends to occur more often on limestone derived calcareous soils that have some rock fragments in the soil profile. Diagnosis: Mesquite, catclaw mimosa, viscid acacia, or creosotebush are the dominant shrubs. Cover of bluestems, alkali sacaton, and giant sacaton is low or absent. Tobosa or burrograss are the dominant grasses. Typically grass cover is patchy with large interconnected bare areas present. Physical soil crusts are present, especially on silt loam surface soils. Transition to Shrub-Dominated (3a, 4a) Reduction of fire, due to either fire suppression policy or loss of adequate fine fuels may increase the probability of shrub encroachment.6 Flood events, livestock and wildlife can transport and disperse shrub seed. Persistent loss of grass cover due to overgrazing or drought can cause large bare patches, providing competition free areas for shrub seedling establishment. As shrub cover increases, competition for soil resources, especially water, becomes a major factor in further reducing grass cover. Key indicators of approach to transition: Decreased grass and litter cover. Increased bare patch size. Increase in amount of shrub seedlings. Transition back Grassland (3b, 4b) Brush control will be necessary to remove shrubs and eliminate competition for resources necessary for grass establishment or reproduction. Range seeding may be necessary if inadequate desired grass species remain in the system. Prescribed grazing will help ensure adequate time is elapsed before grazing is allowed, and proper forage utilization following grass establishment.

State 5
Succulent-Invaded

Community 5.1
Succulent-Invaded

Succulent-Invaded: Succulents, especially tasajillo and cholla may invade the Draw site. Dense stands of tasajillo or cholla are recognized as a management concern, but their impact on grass production is unclear. Light to medium infestations of these succulents does not seem to greatly reduce grass production, however they can reduce access to available forage and interfere with livestock movement and handling. Diagnosis: Cholla and/or tasajillo are present. Grass cover is variable, typically relatively uniform with light infestations of succulents, and becoming patchier with increased amounts of bare ground as succulent densities increase. Tobosa is the dominant grass if from transition 3a. Bluestems or alkali sacaton and giant sacaton are the dominant grasses, if from transition 4a. Transition to Succulent-Invaded (3a, 4a) Succulents may invade and increase on Draw sites due to dispersal of seed and stem parts by flood events, livestock and wildlife. If fire was historically a part of desert grassland ecosystem and played a role in suppressing seedlings of shrubs and succulents, then fire suppression may favor the increase of succulents.1 Key indicators of approach to transition: Decrease or change in distribution of grass cover. Presence of succulents on site. Transition back to Grassland (3b, 4b) Fire is an effective means of controlling cholla and tasajillo if adequate grass cover remains to carry fire.2 Chemical control is effective in controlling cholla and tasajillo; apply when growth starts in May. For light infestations, hand grubbing is also effective if cholla or tasajillo is severed 2-4 inches below ground and care is taken not to let broken joints take root. Stacking and burning piles and grubbing during winter or drought help keeps broken joints and pads from rooting.

State 6
Historic Climax Plant Community 2

Community 6.1
Historic Climax Plant Community 2

1.State Containing Historic Plant Community Swale Type Grass Swale: The historic plant community has a grassland aspect with a few shrubs scattered across the site. This site is associated with the Bottomland ecological site. It occurs as narrow to broad areas, with a sinuous linear slightly concave shape, dissecting adjacent upland, and transporting run-in water to lower Bottomland sites. The draw site stands out in relation to the adjacent uplands, due to the extra water and high production. Tobosa is the dominant grass species, with alkali sacaton and giant sacaton as sub-dominants. Other important species include vine mesquite, blue grama, cane bluestem, and sideoats grama. Mesquite, catclaw mimosa, and fourwing saltbush are common shrubs. This site is resistant to state change unless grass cover on site or surrounding uplands is reduced to the point that accelerated erosion takes place. Severe loss of grass cover due to extended periods of drought or overgrazing may initiate the transition to a gullied state and an increase in shrubs. Diagnosis: Tobosa is the dominant grass species. Grass cover is continuous and uniform. Bare ground is minimal. Shrubs are sparse and evenly distributed. Slopes are nearly level; usually less than three percent, and usually display limited evidence of active rill or gully formation if grass cover remains intact. Litter movement associated with overland flow is limited to smaller size class litter and short distances.

State 7
Gullied State

Community 7.1
Gullied State

Additional States: Gullied State: Loss of grass cover, accelerated erosion, and gully formation characterize this state. Tobosa is the dominant grass species. Vine mesquite, blue grama, cane bluestem, sideoats grama, giant sacaton and alkali sacaton decrease or are extirpated. Burrograss increases and may become sub-dominant to tobosa. Shrub densities may increase especially mesquite, facilitated by increased bare patches. Diagnosis: Tobosa is dominant. Burrograss may be the sub-dominant grass species. Mesquite and other shrubs may be found at increased densities relative to the historic plant community. Grass cover is no longer uniformly distributed, instead tending to be patchy with large areas of bare ground present. Erosion is evident by the presence of water flow patterns, litter dams, rills, and gullies. Transition to the Gullied State (1a): Transitions to the gullied state may occur in response to a loss of grass cover (on or off site), erosion, and changes in hydrology. As grass cover decreases, organic matter and surface soil stability decrease.4, 5 Erosion ensues due to increased flow rates and decreased soil stability. The formation of gullies effectively changes the hydrology, and the site dries. Bare patch size increases providing competition free areas for shrub expansion. 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. Evidence of litter movement—indicating loss or redistribution of organic matter, and decreased surface soil stability. Presence of litter dams, water flow patterns, rills and gullies. Transition back to Grass Swale (1b) 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 grazing.