State 1
Grassland

Community 1.1
Midgrass Prairie

Figure 8. 1. Midgrass Prairie Community

The reference community for this site is a fire-dependent midgrass prairie. Woody species make up less than five percent of the total herbage production. Tobosa, being tolerant of repeated fires, contributes as much as 30 percent composition in the western portion of the area but decreases in dominance from west to east. Sideoats grama, feathery bluestems, vine mesquite (Panicum obtusum), Arizona cottontop (Digitaria californica), Texas cupgrass (Eriochloa sericea), and plain bristlegrass (Setaria leucopila) make up 30 to 45 percent. Buffalograss and curlymesquite are common shortgrasses. Texas wintergrass (Nassella leucotricha), wildryes (Elymus spp), and Western wheatgrass (Pascopyrum smithii) are important parts of the cool-season component. Forbs included Engelmann’s daisy (Engelmannia peristenia), ruellia (Ruellia spp.), sida (Sida spp.), half-shrub sundrop (Calylophus serrulatus), and bundleflower (Desmanthus spp.). Shrubs are scarce but include fire-resistant species like sumac (Rhus spp.), greenbriar (Smilax spp.), pricklypear (Opuntia spp.), and bumelia (Sideroxylon lanuginosum). 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) produced as much as 3,500 pounds in good moisture years and 600 pounds or less in dry years. Annual production declines from east to west due to precipitation differences. Grasses 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 was limited by the dry climate. The Midgrass Prairie Community (1.1) furnishes quality habitat for herbivores.

Community 1.2
Tobosa/Mixed-grass Savannah

Figure 11. 2. Tobosa/Mixed-grass 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 and proper grazing management. The woody canopy varies between 10 and 25 percent depending on length and severity of overgrazing, time since burned, and availability of invading species. Typically, mesquite and/or pricklypear are early and persistent increasers. Condalia (Condalia spp.), algerita (Mahonia trifoliolata), and acacia (Acacia spp.) are also common. The prairie 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 plant community remain, although in lesser amounts.

Annual primary production is reduced slightly in relation to the reference community, ranging from 500 to 3,000 pounds per acre depending on precipitation amounts and the soil series. Grasses remain the dominant producers of forage. Heavy abusive grazing reduced plant cover, litter and mulch and increased bare ground exposing the soil to some 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, a 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 the use of prescribed grazing and prescribed burning conservation practices, the Tobosa/Mixed-grass Savannah Community can revert back to the Midgrass Prairie Community.

State 2
Shrubland

Community 2.1
Mesquite/Mixed-Brush Shortgrass

Figure 14. 2.1 Mesquite/Mixed-Brush Shortgrass Community

The Mesquite/Mixed-brush Shortgrass Community (2.1) is a 30 percent or greater woody plant canopy dominated by mesquite with mixed-brush and pricklypear understory. It is the result of selective overgrazing, absence of fire, and the differential response of plants to defoliation. The diversity of the grassland component declines while woody plants and unpalatable forbs increase. Primary production has decreased due to decline in soil structure and organic matter and is primarily from the woody component. All woody species, except the more palatable ones, have increased in size and density. The typical woody cover is scattered oak trees or mottes, with mesquite and pricklypear common understory species. Algerita, acacia, condalia, and snakeweed (Gutierrezia spp.) are also common in places.

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 continued overgrazing, tobosa gives way to buffalograss (Bouteloua dactyloides), curlymesquite (Hilaria belangeri), and other less palatable shortgrasses and forbs. 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 common. Cool-season grasses such as Texas wintergrass can be found under and around woody plants. In wet cycles, grasses such as bromes (Bromus spp.), and other annual species such as broomweed (Amphiachyris spp.) are abundant. Because of grazing pressure and competition for nutrients and water from the woody plants, the grassland component shows lack of plant vigor and productivity.

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.

Annual primary production is approximately 500 to 3,000 pounds per acre, which is dominated by the mesquite, pricklypear, and other mixed-brush components. As this plant community nears maturity, the herbaceous component contributes less than 30 percent of the annual total production. Browsing animals such as goats and deer find fair food value in this plant community if browse resources have not been grazed excessively. Forage quantity and quality for cattle is low. Livestock stocking decisions should consider the species composition and quantity of available forage and set-stocking rates accordingly.

Unless brush management and good grazing management are applied, the continued transition toward dense shrubland will continue. The trend cannot be reversed with good grazing management practices alone. Renovation type brush control practices are required to reverse the trend toward dense shrubland. Alternatives for restoration include: brush management, range planting to return vegetation back to reference species, proper grazing management, and prescribed burning to maintain the desired community.

State 3
Converted Land

Community 3.1
Converted Land

Figure 17. 3.1 Cropland Community

Figure 18. 3.1 Pastureland Community

Early settlers, having a farming background, cultivated small fields on the Clay Flat and adjacent Clay Loam and Bottomland sites for vegetable crops, grain, forage sorghum and winter cereals for livestock forage. Many acres of the were converted to cropland. The potential for cropland is high. Many areas of the Clay Flat site are associated with other arable soils and could be converted to cropland. Cropping small acreages is practiced for summer annual forage crops or winter small grain grazing especially if irrigation water is available. 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 often seeded to native or introduced species such as Kleingrass (Panicum coloratum). Herbage production on those seeded to adapted introduced grasses or native grasses can reach peak production within a few years if a full stand is established. In this case, herbage production will equal the reference community. Adapted introduced species plantings such as Kleingrass may surpass reference community production depending upon the degree of cultivation induced soil deterioration. The practice of including adapted legumes or other forbs to the grass mixture will enhance vegetative productivity and usefulness on the land, especially for wildlife.

Invasion of the seeded fields by brush, particularly mesquite and pricklypear, is common in this site. Drought and reduced soil cover due to cropping 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 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 abusive grazing pressure, no fires, no brush management, no pasture/cropland management, abandonment, and idled land conditions, the Converted Land Community would shift to the Abandoned Land Community.

Pathway 3.2A
Community 3.2 to 3.1

Prescribed grazing, range/pasture/cropland management, pasture planting, range planting, and crop cultivation are several of the conservation practices necessary to revert back to the Converted Land Community.

Transition T1A
State 1 to 2

The changes in species composition are small initially. Unless proper grazing and prescribed burning are initiated at this stage, the invading species continue to increase in size and density. When the canopy of the woody plants becomes dense enough (25 percent) and tall enough (greater than five 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 effectively control the brush with prescribed burning. Once this threshold is passed, the Tobosa/Mixed-grass Community (1.2) transitions into the Mesquite/Mixed-brush Shortgrass Community (2.1) a plant community state in which normal range management practices, such as proper grazing and prescribed burning, cannot reverse the trend to woody plant dominance.

Transition T1B
State 1 to 3

The Grassland State can shift to the Converted Land State through the implementation of various practices such as brush management, pasture planting, range planting, and crop cultivation.

Restoration pathway R2A
State 2 to 1

The Shrubland State can be reverted back to the Grassland State through the application of various conservation practices including prescribed grazing, brush management, IPT, range planting, and prescribed burning.

Transition T2A
State 2 to 3

With the use of brush management, pasture planting, range planting, and crop cultivation, the Shrubland State shifts to the Converted Land State.