State 1
Midgrass Savannah

Community 1.1
Midgrass Savannah

The reference plant community for this site is a savannah composed of midgrasses with scattered trees and shrubs which have evolved under the influence of grazing, periodic fire, and fluctuations between wet and dry periods, often lasting years at a time. The production on the site varies greatly over the years due to the episodic nature of the rainfall. The overstory shades up to 10 percent of the site and consists primarily of mesquite (Prosopis glandulosa), hackberry (Celtis laevigata), western soapberry (Sapindus saponaria), and occasional live oaks (Quercus virginiana), with shrubs such as algerita (Mahonia trifoliata), ephedra (Ephedra spp.), littleleaf sumac (Sumac spp.), condalia (Condalia spp.), wolfberry (Symphoricarpos orbiculatus), and fourwing saltbush (Atriplex canescens). Mesquite tree size diminishes from east to west. Midgrasses such as sideoats grama (Bouteloua curtipendula), cane bluestem (Bothriochloa barbinoidis), silver bluestem (Bothriochloa laguroides), and plains bristlegrass (Setaria leucopila) dominate the site. Subdominants include Arizona cottontop (Digitaria californica), buffalograss (Buchloe dactyloides), tobosa (Hilaria mutica), Texas wintergrass (Nassella leucotricha), and Canada wildrye (Elymus canadensis). Perennial forbs are a small, but important, component of the plant community. Plants are vigorous and reproduction by rhizome, stolon or seed is rapid during favorable weather. Bare ground is less than 25 percent. Interspaces between plants are mostly covered with litter. The soil surface is relatively cool, moderately rich in humus, and hosts a healthy microbe population actively decomposing organic matter. Soil erosion is insignificant. Infiltration is complete for most rainfall events and runoff occurs only during heavy rains when overland flow is high. Concentrated water flow patterns are rare. Recurrent fire, climatic patterns and grazing by bison, pronghorn and other herbivores were natural processes that maintained this historic plant community.

Interruption of the ecological processes of a site brings about change. The reference plant community included large populations of desirable grasses and forbs. However, continued overuse and drought have resulted in their disappearance from large portions of the site. As fire is eliminated and overstocking becomes continual, the more palatable grasses such as sideoats grama, cane bluestem, Texas cupgrass (Eriochloa sericea), Arizona cottontop, plains bristlegrass, Canada wildrye, and vine mesquite (Panicum obtusum) decrease as do the palatable perennial forbs, while unpalatable short and annual grasses and forbs, shrubs, succulents, and trees take the place of these more desirable plant species. Encroachment by small mesquite, various shrubs and prickly pear cactus commences. More bare ground appears. The diversity of native forbs and grasses has been significantly reduced, while the presence of introduced and native invader species seems to be increasing annually. The community shifts toward the Mid and Shortgrass Mesquite Savannah Community. With institution of sound management practices, however, this trend can be reversed, and a measure of productivity restored. Understanding the ecology of the site and use of sound grazing management, individual plant treatment and prescribed burning where practical are keys to any attempts to return to the reference community.

Community 1.2
Mid/Shortgrass Mesquite Savannah

This community still resembles a midgrass savannah plant structure to casual observation. However, due to the measurable decline of dominant midgrasses caused by overstocking, elimination of fire, lack of brush management and, possibly changes in weather patterns, the population of mesquite and other woody species begins to increase. Vigor and reproduction of the historically dominant grass species decline, and they are starting to be replaced by tobosa, buffalograss, curlymesquite (Hilaria belangeri), slim tridens (Tridens muticus), Hall’s panicum (Panicum hallii) and other short grasses. Less palatable annual and perennial forbs increase. Ground cover by litter decreases. Up to 40 percent of the ground is bare. Soil organic matter is decreasing. Infiltration begins to drop off and runoff increases. Signs of erosion begin to appear. The loss of topsoil and soil organic matter makes it very hard for these abused areas to return to the historic plant community within a reasonable period.

The retrogression at this point can be reversed with relatively small labor and cost input if measures are taken soon enough. Application of prescribed grazing is essential to stop the decline of high quality midgrasses and forbs. Prescribed burning can be used in some rainfall areas to control small woody plants and their seedlings. These can also be controlled through individual plant treatment mechanically or with appropriate chemical application.

Pathway 1.1A
Community 1.1 to 1.2

With heavy abusive grazing, no brush management, brush invasion, and no fires, the Midgrass Savannah Community will shift to the Mid/Shortgrass Mesquite Savannah Community.

Pathway 1.2A
Community 1.2 to 1.1

With prescribed grazing, brush management, IPT, and prescribed burning, the Mid/Shortgrass Mesquite Savannah Community can be reverted back to the Midgrass Savannah Community.

State 2
Shortgrass Savannah

Community 2.1
Shortgrass Mesquite/Mixedbrush Savannah

This community represents a significant vegetation shift, crossing the threshold from the Savannah State to the Shortgrass Mesquite/Mixed Brush Savannah community. The major woody increaser species, primarily mesquite, have multiplied until they comprise up to 20 percent of the overstory canopy and exert strong influence on the site, with total grass production severely restricted. The reference community midgrasses are almost gone, grazed or shaded out, and short grasses are predominant. The Texas wintergrass population becomes significant. Palatable perennial forbs are scarce. The proportion of toxic plants increases; some of the more common include western bitterweed (Hymenoxys odorata), African rue (Peganum harmala) (an introduced invader species mostly associated with oilfield activity), paperflower (Psilostrophe cooperi), perennial broomweed (Amphiachyris spp.), peavine (Lathyrus spp.), and groundsel (Senecio spp.) species. This site exhibits mesquite up to 15 feet, as well as major increases in shrubs such as condalia, algerita, pricklyash (Zanthoxylum clava-herculis), redberry juniper (Juniperus pinchotti), and succulents like prickly pear (Opuntia spp.). Redberry juniper is an invader and will be more apparent when the site is in proximity to limestone hill or low stony hill ecological sites. Tarbush (Flourensia cernua) may invade from adjacent loamy ecological sites.

Up to 60 percent of the ground is bare, which lends itself to a proliferation of annual forbs in some years, particularly when a wet fall/winter follows a dry spring/summer. Some, such as filaree (Erodium texanum) or redseed plantain (Plantago rhodosperma), provide a certain amount of high-quality forage for sheep, goats, and deer during winter and early spring, but quickly dry up when summer arrives. Litter is scarce and organic matter is low. Less water infiltrates and runoff increases. Topsoil loss through erosion accelerates, evidenced by plants on pedestals, rills, and stunted plant growth. Sheet erosion, though not easily detected visually, is high, particularly when the site is between a steep watershed and a draw or stream. If proper management is not planned and implemented, the site will continue to degrade and the community will shift toward a Mesquite/Mixed Brush Complex Community. By implementing conservation measures such as brush management (chemical, mechanical or, in specific cases, using biological species such as sheep and goats), range seeding (not recommended in areas of less than 18 inches annual rainfall), prescribed grazing and prescribed burning where appropriate, the land manager can possibly shift the community back toward a Midgrass Savannah community.

State 3
Mesquite Complex

Community 3.1
Mesquite/Mixed Brush Complex

The Mesquite/Mixed Brush Complex is the result of an extreme shift of site characteristics from the original Midgrass Savannah Community. Mesquite and other woody increasers and invaders dominate, with canopy cover ranging from 20 percent upward. Their strong competition for water, sunlight and nutrients has severely limited or eliminated short grass populations, let alone the original midgrass community. Species such as hairy tridens (Erioneuron pilosum), red grama (Bouteloua trifida), Texas grama (Bouteloua rigidiseta), burrograss (Scleropogon brevifolius), various threeawns (Aristida spp.), tobosa, and annuals dominate the grass plant population of this site. If the woody population is primarily large mesquite trees, a significant amount of Texas wintergrass may develop, often in conjunction with prickly pear. The forb component consists predominantly of annuals or unpalatable perennials. More than 80 percent of the ground can be bare of grasses and forbs.

Often most of the original, fertile topsoil has eroded away. Gullies may have formed. Bare soil has crusted and is relatively impermeable. However, under a heavy canopy of mesquite, juniper and/or mixed brush a buildup of leaf/needle litter occurs, which improves infiltration and helps retard erosion. This community very likely cannot be restored to the reference plant community. Decades of transition from a Midgrass Savannah Community (1.1) have negatively impacted soil properties, species diversity, site integrity, and hydrology features. However, the site can be reclaimed. Reclamation involving brush management with heavy equipment, aerial spraying, reseeding native grasses and forbs where rainfall is adequate, prescribed grazing, and reintroduction of fire through prescribed burning can restore the site to a semblance of its former self, but it will probably never completely reflect the original. It can, however, be maintained in a productive, stable state for grazing and, when native plants can be seeded and maintained, beneficial to wildlife.

State 4
Reclamation

Community 4.1
Open Grassland

This community is the product of endeavors to reclaim the Mesquite/Mixed Brush Complex or, less frequently, the Shortgrass Mesquite/Mixed Brush Savannah Community. Depending on the goals of the land user, reclamation efforts might involve the whole site or only part of it. A land manager involved primarily with livestock might prefer more open, grassy areas, whereas one interested mostly in wildlife would probably want to leave substantial brushy areas.

Through brush management, reseeding of native species (both grasses and forbs) in areas of adequate rainfall, prescribed grazing and re-introduction of fire where appropriate, one can possibly manipulate this site successfully towards a reference community appearance, but it will never be able to mirror the original site. However, utilizing natives as the reseeding source will greatly benefit wildlife species such as deer, turkey, quail, and other birds.

This Open Grassland Community may also be comprised of seeded species which are non-native and which may occur as a monoculture community. This type may contain less cover or food for wildlife, often practically devoid of native grasses and forbs. The annual production was taken from the variations of the plant species that are described in this plant community.

The site’s capacity to produce must be determined over time under careful management. Maintenance through prescribed grazing, prescribed burning and individual plant treatment with appropriate chemicals can preserve the site’s sustained production indefinitely. Without these measures, the site will experience renewed encroachment of mesquite and other increasers/invaders.

Community 4.2
Open Grassland with Mesquite Encroachment

This community is a man-induced Open Grassland Community that has an encroachment of woody species. Through the re-introduction of prescribed burning, prescribed grazing, and individual plant treatment, this site can successfully be shifted back toward the Open Grassland Community and remain very productive. If these management alternatives are not implemented in a timely manner, this site will become reinfested with woody species. Over a period of years or possibly decades, it will again become heavily infested with brush and will have limited forage productivity, subsequently reverting to the Mesquite/Mixed Brush Complex.

Pathway 4.1A
Community 4.1 to 4.2

With heavy abusive grazing, no brush management, brush invasion, no fires, and drought conditions, the Open Grassland Community will shift to the Open Grassland/Mesquite Encroachment Community.

Pathway 4.2A
Community 4.2 to 4.1

With prescribed grazing, brush management, IPT, and prescribed burning, the Open Grassland/Mesquite Encroachment Community will revert back to the Open Grassland Community.

Transition T1A
State 1 to 2

With heavy abusive grazing, no brush management, brush invasion, no fires, and drought conditions, the Midgrass Savannah State will transition to the Shortgrass Savannah State.

Restoration pathway R2A
State 2 to 1

With prescribed grazing, brush management, individual plant treatment (IPT), range planting, and prescribed burning conservation practices, the Shortgrass Savannah State can be reverted back to the Midgrass Savannah State.

Transition T2A
State 2 to 3

With heavy abusive grazing, no brush management, brush invasion, no fires, and drought conditions, the Shortgrass Savannah State will transition to the Mesquite Complex State.

Transition T3A
State 3 to 4

With heavy abusive grazing, no brush management, brush invasion, no fires, and drought conditions, the Mesquite Complex State can be transitioned to the Reclamation State.

Transition T4A
State 4 to 3

With heavy abusive grazing, no brush management, brush invasion, no fires, and drought conditions, the Reclamation State State will transition to the Mesquite Complex State.