State 1
Grassland

Community 1.1
Midgrass Prairie

Figure 8. 1.1 Midgrass Prairie Community

The reference community for this site is a fire induced midgrass prairie. Woody species make up less than five percent of the total herbage production. Tobosa, being tolerant of repeated fires, made up as much as 20 percent. Sideoats grama, feathery bluestems, vine mesquitegrass, Arizona cottontop (Digitaria californica), Texas cupgrass (Eriochloa sericea), and plain bristlegrass contribute 30 to 60 percent. Buffalograss and curlymesquite were common shortgrasses. Texas wintergrass (Nassella leucotricha), wildrye (Elymus spp.), and western wheatgrass (Pascopyrum smithii) were important parts of the cool-season grass component. Forbs include Engelmann’s daisy (Engelmannia peristenia), ruellia (Ruellia spp.), sida (Sida spp.), verbena, groundcherry (Physalis spp.), and bundleflower (Desmanthus spp.). Shrubs are scarce but include fire-resistant species as sumac (Rhus spp.), pricklypear (Opuntia spp.), and condalia (Condalia spp.). Oaks (Quercus spp.) and mesquite (Prosopis spp.) are also present but are usually scattered multi-stemmed shrubs created by repeated wildfires. The Midgrass Prairie Community (1.1) produce as much as 3,000 pounds in good moisture years and as little as 600 pounds in dry years. Annual yields decline from east to west due to precipitation differences. Grasses and forbs contribute up to 95 percent of the total annual production. The midgrasses aid in the infiltration of rainfall into the moderately permeable soil and reduced runoff. Litter and organic matter buildup is limited by the dry climate. The Midgrass Prairie Community (1.1) furnishes good forage for grass eating type animals such as bison, pronghorn antelope, horses, and cattle.

Community 1.2
Tobosa/Mixed-grass Savannah

Figure 11. 1.2 Tobosa/Midgrass Savannah Community

The Tobosa/Mixed-grass Savannah Community (1.2) is a tobosa dominated mixed-grass community being encroached by woody species that have been held at low densities by repeated fires and competition from a vigorous grass component. Brushy species, including pricklypear and mesquite, increase in density because heavy abusive grazing by livestock reduces grass cover, causes reduction of soil cover, and reduces fine fuel necessary to care fires. Due to selective grazing and differential response of plants to defoliation, heavy grazing also causes changes in composition of the reference community. The more palatable midgrasses and forbs are replaced by less palatable, or more grazing resistant, species. The encroaching woody species are generally less than five feet tall and subject to control by prescribed burning. The woody canopy varies between 5 and 15 percent depending on length and severity of overgrazing, frequency and duration of fires, and seed sources by invading species. Typically, mesquite and/or pricklypear are early and persistent increasers. Condalia (Condalia spp.), algerita (Mahonia trifoliolata), broom snakeweed, and acacia (Acacia spp.) are also common. The prairie grassland becomes a grassland-shrub savannah being encroached by suppressed woody species. The preferred midgrasses are being replaced by the more grazing resistant tobosa, although sideoats grama, vine mesquite, Texas cupgrass, and feathery bluestems persist in this phase. Most of the perennial forbs found in the reference community remain, although in lesser amounts. Annual primary production is reduced slightly relative to the reference community, ranging from 500 to 2,500 pounds per acre depending on precipitation amounts and the specific soil series. Grasses remain the dominant producers of forage. Heavy abusive grazing reduces plant cover, litter, and mulch, and increases bare ground which exposes the soil to erosion. There could be some mulch and litter movement during rainstorms but due to gentle slopes, little soil movement takes place in this vegetation phase.

Pathway 1.1A
Community 1.1 to 1.2

Midgrass Prairie

Tobosa/Mixed-grass Savannah

The reference community can be maintained with prescribed grazing and prescribed burning. Stocking rates must consider the kind of livestock and balance their numbers with current annual forage production while considering competition from other herbivores. With heavy abusive grazing, decrease in intensity and frequency of fires and no brush management, this plant community transitions very quickly to the Tobosa/Mixed-grass Savannah Community (1.2).

Pathway 1.2A
Community 1.2 to 1.1

Tobosa/Mixed-grass Savannah

Midgrass Prairie

With prescribed grazing, prescribed burning, brush management, and IPT, the Tobosa/Mixed-grass Savannah Community can revert back to the Midgrass Prairie Community.

State 2
Shrubland

Community 2.1
Tobosa/Shortgrass Mesquite/Mixed-Brush

Figure 14. 2.1 Shortgrass Mesquite/Mixed-Brush Community

The Tobosa/Shortgrass Mesquite/Mixed-Brush Community (2.1) presents a 15 to 35 percent woody canopy cover dominated by mesquite with mixed-brush and a shortgrass understory. This community is the result of selective heavy grazing by livestock, suppression of fire, and the differential response of plants due to defoliation. The diversity of the grassland component declines while woody plants and unpalatable forbs increase. Primary production decreases due to decline in soil structure and organic matter and is primarily from the woody component instead of the grass-like component. All, except the more palatable woody species, have increased in size and density. Mesquite typically dominates the overstory and pricklypear dominates the understory. Algerita, acacia, condalia, and broom snakeweed may also be present in this community. Remnants of reference community may occupy interspaces between trees and shrubs, but more often they are unpalatable invader species. Tobosa remains dominant, but as regression progresses under heavy grazing pressure, tobosa gives way to buffalograss (Buchloe dactyloides), curlymesquite (Hilaria belangeii), and other less palatable shortgrasses. Mexican sagewort (Artemesia ludoviciana), Texas nightshade (Solanum spp.), queen’s delight (Stillingia sylvatica), prairie coneflower (Ratibida columnifera), Texas grama (Bouteloua rigidiseta var. rigidiseta), and red grama (Bouteloua trifida) are commonly found in this community. Cool-season grasses such as Texas wintergrass can be found under and around woody plants. In wet cycles, bromes (Bromus spp.) and other annual species such as broomweed (Gutierrezia spp.) are abundant. Annual primary production is approximately 500 to 2,000 pounds per acre, depending on precipitation events. Herbage production is balanced between the grassland component and woody species. As the grassland component declines, more soil is exposed to crusting and wind erosion. During the middle and end of this plant community phase, considerable soil becomes exposed further. Water erosion is not a serious problem because of the shallow slopes on the site but wind erosion can be rather high. High interception losses by the increasing woody canopy combined with evaporation losses can reduce the effectiveness of rainfall. Litter, soil organic matter and structure decline in the interspaces reducing water infiltration but hydrologic conditions improve under the woody plant cover.

Community 2.2
Mesquite/Mixed-Brush Shortgrass

Figure 17. 2.2 Mesquite/Mixed-Brush Shortgrass Community

The Mesquite/Mixed-Brush Shortgrass Community (2.2) is dominated by mesquite and shrubs with few shortgrasses present. Remnants of the reference grassland vegetation, mostly shortgrasses and shade tolerant forbs, occupy the shrub interspaces. This community is the result of selective heavy grazing by livestock and wildlife, absence of natural fires and the differential response of plants due to defoliation on the shrubland site. The typical woody canopy is mesquite with pricklypear in the understory. Algerita, acacia, condalia, and snakeweed are also common in this community. Tobosa remains dominant initially; but as regression progresses under heavy grazing pressure, tobosa gives way to buffalograss, curlymesquite, and other less palatable species. Mexican sagewort, Texas nightshade, queen’s delight, prairie coneflower, Texas grama, and red grama become common. Cool-season grasses such as Texas wintergrass can be found under and around woody plants. During wet periods, bromes and other annual species such as broomweed are abundant. Because of grazing pressure and competition for nutrients and water from the woody plants, the grassland component shows a lack of plant vigor and productivity. As the grassland component declines, more soil is exposed to crusting and wind erosion. During the beginning and middle of this plant community phase, considerable soil becomes exposed. Water erosion is not a serious problem because of the shallow slopes, but wind erosion can be rather high. High interception losses by the increasing woody canopy combined with evaporation losses can reduce the effectiveness of rainfall. Litter, soil organic matter and structure decline in the interspaces reducing water infiltration in the interspaces, but hydrologic conditions improve under the woody plant cover. Browsing animals can find fair quality food sources if deer and goat browsing have not been excessive. Forage quantity and quality for cattle in this plant community is low. Livestock stocking decisions should consider the forage species composition, quantity of available forage, and rangeland health conditions to determine the proper annual carrying capacity. Unless brush management and prescribed grazing management are applied, the transition toward dense shrubland will continue. Brush control practices are required to reverse the continuing trend of a brush canopy enclosure. To restore livestock or deer production, brush management is required to remove undesirable brush species, range planting of native species to return vegetation, and establish prescribed grazing and prescribed fire conservation practices to maintain the health of the desired plant community. Caution should be applied in choosing brush control and seeding methods. Broadcast herbicides are often ineffective and mechanical treatments that expose soil leave the site open which can lead infestation of weeds that often can persist for several years.

Pathway 2.1A
Community 2.1 to 2.2

Tobosa/Shortgrass Mesquite/Mixed-Brush

Mesquite/Mixed-Brush Shortgrass

When the shrub canopy cover nears 35 percent and the herbaceous component contributes less than 50 percent of the herbage production, the plant community crosses the threshold and becomes a Mesquite/Mixed-Brush Shortgrass Community (2.2).

Pathway 2.2A
Community 2.2 to 2.1

Mesquite/Mixed-Brush Shortgrass

Tobosa/Shortgrass Mesquite/Mixed-Brush

With the implementation of brush management, prescribed grazing, and prescribed burning, the Mesquite/Mixed-brush Shortgrass Community can revert back to the Tobosa/Shortgrass Mesquite/Mixed-brush Community.

State 3
Converted Land

Community 3.1
Converted Land

The Clay Flat is used mainly for rangeland production but some areas are still cultivated. Potential for cultivated crops is higher with irrigation than by dryland cropping systems. Without irrigation, crop agriculture is not sustainable in this semiarid climate. Cropping small acreages is practiced in either summer annual forage crops or winter small grain grazing. Many fields, however, have been abandoned and let ‘go back’ to native range or planted to native or introduced grasses for pasture. Cropland areas are seeded to native or introduced species such as Kleingrass (Panicum coloratum) or Old World bluestem (Bothriochloa spp.). Production on those seeded to adapted introduced grasses or native grasses can reach peak production within a few years, once a full stand becomes established. In this case, herbage production will equal the reference community if native species are seeded. Adapted introduced species plantings such as Kleingrass may surpass reference community production. The practice of including adapted legumes or other forbs will enhance productivity and usefulness, especially for wildlife. Invasion of the seeded fields by brush, particularly mesquite and pricklypear, is common. Drought and reduced soil cover due to crop cultivation and heavy abusive grazing along with a nearby seed source trigger the brush invasion. The shrubs that appear in seeded or abandoned fields are established by seeds brought in by animals, water, or wind. The invading brush must be controlled with grazing management, prescribed burning, or other appropriate brush management methods, or the woody invaders will dominate.

Community 3.2
Go Back Land

The Go Back Land Community (3.2) is used to describe cropland fields that have been abandoned and are undergoing secondary succession. The Go Back Land Community results from abandoning cropped land and leaving it idle without seeding or brush management. Many cropland areas have been abandoned and are invaded by brush from the adjacent rangeland. The initial composition of abandoned fields is composed of annual, biennial, and weak perennial grasses and forbs. The species depends on the seed source from adjacent areas. The rate of succession depends on grazing management and drought frequency, but the reestablishment of reference community species takes many years. Without grazing management and brush management practices, brush species such as pricklypear, mesquite, and juniper will dominate the site before a grass community can establish. Biomass production will be limited in the early seral stage and increase as the plant community develops. Brush management and grazing management are necessary to allow the field to go back to the reference community.

Pathway 3.1A
Community 3.1 to 3.2

With abandonment, invasion of brush, no brush management, heavy abusive grazing, no pest management, and no nutrient management, the Converted Land Community will shift to the Go Back Land Community.

Pathway 3.2A
Community 3.2 to 3.1

With crop cultivation, plowing, pasture planting, nutrient management, pest management, and prescribed grazing conservation practices, the Go Back Community can revert back to the Converted Land Community.

Transition T1A
State 1 to 2

The changes in species composition are small initially, but unless proper grazing and prescribed burning are initiated; the invading species continue to increase in size and density. When the canopy of the woody plants becomes dense enough (15 percent) or tall enough (greater than 5 feet) to suppress grass growth and resist fire damage, a threshold in ecological succession is crossed. This threshold can also occur when the fine fuel load provided by grasses is too low to control brush effectively with fire. The Tobosa/Mixed-grass Savannah Community (1.2) then becomes the Tobosa/Shortgrass Mesquite/Mixed-Brush Community (2.1). In this plant community, normal range management practices, such as prescribed grazing, cannot reverse the trend to woody plant dominance.

Transition T1B
State 1 to 3

With crop cultivation, plowing, pasture planting, nutrient management, pest management, and prescribed grazing conservation practices, the Grassland State can be converted into the Converted Land State.

Restoration pathway R2A
State 2 to 1

With the application of various conservation practices such as prescribed grazing, prescribed burning, brush management, IPT, and range planting, the Shrubland State could revert back to the Grassland State.

Transition T2A
State 2 to 3

With crop cultivation, plowing, pasture planting, nutrient management, pest management, and prescribed grazing, the Shrubland State shifts to the Converted Land State.