State 1
Grassland

Community 1.1
Midgrass Dominant

This community represents the reference community. It is a fire climax, midgrass plant community that has less than five percent canopy of woody plants. The grasses are false Rhodesgrass, multi-flower chloris, little bluestem, Arizona cottontop, feather bluestems, pink pappusgrass, sideoats grama, buffalograss (Bouteloua dactyloides), curlymesquite (Hilaria belangeri), perennial threeawn (Aristida spp.), plains bristlegrass (Seteria spp.), Texas wintergrass (Nassella leucotricha), and hooded windmillgrass (Chloris cucullata). The woody species are mesquite, whitebrush, condalias, spiny hackberry (Celtis pallida), cacti, Texas colubrine (Colubrina texensis), wolfberry, vine ephedra (Ephedra spp.), desert yaupon (Schaefferia cuneifolia), and guayacan (Guaiacum angustifolium). Forbs are Engelmann’s daisy (Engelmannia peristenia), bundleflower (Desmanthus spp.), sensitive briar (Mimosa spp.), orange zexmenia (Wedelia texana), hairy ruellia (Ruellia spp.), Mexican sagewort (Artemisia ludoviciana), bushsunflower (Simsia calva), lazy daisy (Aphanostephus spp.), and annual forbs.

Recurrent fire and grazing by bison and other wildlife were natural components of the ecosystem. Settlement by European man brought continuous overstocking with no natural fires and the eventual removal of sheep. These changes caused a drastic change in the plant communities. The midgrasses gave way to the shortgrasses and the brush started to increase, causing a shift to the Shortgrass Dominant Community (1.2) and the Mixed-grass Dominant Community (1.3). Each of these communities can be managed back to the Midgrass Dominant Community (1.1) using prescribed grazing and fire. The Mixed-grass Dominant Community (1.3) may also require selective brush management or Individual Plant Treatments (IPT). However, once the woody canopy exceeds 20 percent and is taller than thre feet, the site transitions to the Shrub/Woodland State (2). In this case, energy in the form of heavy equipment, herbicides and prescribed grazing are required to shift the plant community back to the Grassland Savannah State (1). The Grassland Savannah State (1) can be converted to the Converted Land (3) state by controlling the brush and seeding to native or introduced grasses. It may also be plowed and converted to cropland.

Community 1.2
Shortgrass Dominant

This phase of the Grassland Savannah State still exhibits a savannah plant structure with the woody species canopy being as high as 10 percent, but less than three feet tall. This is a result of fire being removed as a component of the site. Heavy continuous grazing has taken many of the midgrasses out of the site and replaced them with shortgrasses such as buffalograss, curlymesquite, threeawn, tumblegrass (Schedonnardus paniculatus), and red grama (Bouteloua trifida). Other common Increasers to the site are leatherstem (Jatropha dioica), huisache (Acacia smallii), ragweed (Ambrosia spp.), and tasajillo (Opuntia leptocaulis).

Community 1.3
Mixed-grass Dominant

This phase of the Grassland Savannah State still exhibits the savannah plant structure even though the woody canopy cover may be as high as 20 percent. The understory can still be a midgrass plant community, a shortgrass community, or a mixture of midgrasses and shortgrasses depending on the grazing management regime that it has received. A lack of fire and brush management is the major component driving the plant community toward Shrub/Woodland State (2). A threshold is being approached, but is still reversible by prescribed fire, brush management, and grazing management. There is still sufficient fuel production to carry a fire and the shrubs are small enough to still be affected.

Pathway 1.1A
Community 1.1 to 1.2

The reference community (1.1) will transition to the Shortgrass Dominant Community (1.2) with lack of fire, continued overgrazing, insufficient rest cycles, and/or natural disturbances, like prolonged drought.

Pathway 1.2A
Community 1.2 to 1.1

This phase can be managed back to the Midgrass Dominant Community (1.1) but will take the reintroduction of fire to the ecosystem or some method of brush management that allows selective removal of the plants. A prescribed grazing plan will be essential to reverse the trend and return the midgrasses back to the plant community over an extended period of time.

Pathway 1.2B
Community 1.2 to 1.3

If heavy continuous grazing continues with the exclusion of fire, the phase will transition to the Mixed-Grass Dominant Community (1.3).

Pathway 1.3A
Community 1.3 to 1.2

This phase can be managed back to the Community 1.2, and eventually 1.1 but will take the reintroduction of fire to the ecosystem or some method of brush management that allows selective removal of the plants. A prescribed grazing plan will be essential to reverse the trend and returning the shortgrasses, and eventually the midgrasses back to the plant community over an extended period of time.

State 2
Shrub/Woodland

Community 2.1
Shrubland

This plant community is a result of a transition from the Grassland Savannah (1) to the Shrubland/Woodland State (2). This threshold is passed when the woody canopy becomes such that insufficient fuel is produced to carry a fire that will control the woody canopy. The understory is limited in production due to the competition for sunlight, water, and nutrients. There is an increase in tasajillo, prickly pear (Opuntia spp.), yucca (Yucca spp.), annual grasses, and forbs.

Community 2.2
Woodland

This plant community is the culmination of continued heavy grazing and a lack of fire or brush management. At this point the woody species have dominated the site and there is very little understory production. Bare ground has increased and caused crusting to the point that there is little water infiltration and little seedling emergence. Water infiltration does occur directly under some of the woody species, such as mesquite, as it moves down the trunk of the tree to the base. During the growing season, light showers are captured in the canopy of the trees and evaporate. Energy flow is predominantly through the shrubs as is the nutrient uptake. Winter rains can produce understory forage from cool-season annual forbs and grasses and perennials such as Texas wintergrass.

Pathway 2.2A
Community 2.2 to 2.1

To transition Community 2.2 back to 2.1, the land manager will need to apply prescribed grazing, prescribed burning (if enough fuel loads still exist), and brush management. The key is lessening the canopy cover by woody species.

State 3
Converted Land

Community 3.1
Converted Land

This plant community is a phase of the Converted Land State developed by applying brush management and seeding. The area can be seeded to native grasses, forbs, and desirable woody species, singly or as a mix. To maintain the native planting, prescribed grazing and some form of brush control will be needed on a continuing basis or the plant community will develop into the Woody Seedling Encroachment Community (3.2).

Some land managers have chosen to seed introduced grasses instead of native species. To maintain the introduced grass planting, prescribed grazing and some form of brush control will be needed on a continuing basis or the plant community will develop into the Woody Seedling Encroachment Community (3.2). This community can also be attained by converting cropped fields into pastures.

Some sites remain in cropland today, typically small grain production for stocker-cattle grazing. While restoration of this site to a semblance of the midgrass grassland is possible with range planting, prescribed grazing, and prescribed burning, complete restoration of the reference community in a reasonable time is very unlikely due to deterioration of the soil structure and organisms. If cropping is abandoned, this land is usually planted to introduced grasses and forbs and managed as pastureland or encroachment by woody seedlings occur.

Community 3.2
Woody Seedling Encroachment

This plant community develops from native seeding, introduced seeding, and abandoned cropland communities. Seedlings of shrubs establish and spread due to the lack of fire or some other method of brush management. If the seedlings are not controlled, the Converted Land Community (3.1) will transition to the Woody Seedling Encroachment Community (3.2) and will require the application of energy in the form of machinery or herbicides to reduce the canopy. Production of the seeded species depends on the grazing management that has been applied since seeding, and the canopy of the shrubs invading or increasing on the site. As the canopy of the shrubs expands, grass and forb production will be reduced. Production will depend on the grass and forb species that invade the site as well as the canopy of the shrub invasion. It is unlikely that the Converted Land State (3) will ever fully return to the Grassland Savannah State (1). If neglected for a long time, it will transition into a Shrub/Woodland.

Pathway 3.2A
Community 3.2 to 3.1

In order to return to the Converted Land Community (3.2), the land manager must control the woody encroachment. This can be attained by mechanical or chemical brush management techniques. Proper grazing and fire may help if the system is planted in grass. If the system is being cropped, other mechanical and chemical means are necessary to return the site to full agricultural productivity.

Transition T1A
State 1 to 2

Once the woody canopy exceeds approximately 20 percent and is taller than three feet, a threshold will have been passed to the Shrub/Woodland State (2). In this case energy in the form of heavy equipment and/or herbicides will be required along with prescribed grazing to shift the plant community back to the Grassland Savannah State (1).

Transition T1B
State 1 to 3

The Grassland Savannah State (1) can be converted to the Converted Land State (3) by controlling the brush and seeding to native or introduced grasses. It may also be plowed and converted to cropland.

Restoration pathway R2A
State 2 to 1

Brush management is the key driver in restoring Shrub/Woodland State (2) back to the Grassland Savannah State (1). Reduction in woody canopy below 20 percent will take large energy inputs depending on the canopy cover. A prescribed grazing plan and prescribed burning plan will keep the state functioning.

Transition T2A
State 2 to 3

The Shrub/Woodland State (2) can be converted to the Converted Land State (3) by controlling the brush and seeding to native or introduced grasses. It may also be plowed and converted to cropland.

Transition T3A
State 3 to 2

If the Woody Plant Seedling Encroachment Community (3.2) is left alone, eventually the woody plants will create a moderate to heavy canopy. At this point, the desired understory grasses, forbs, and/or crops will be shaded out and the site will transition into a Shrub/Woodland State (2).