State 1
Grassland

Community 1.1
Midgrass Prairie

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, 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. 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 are limited by the dry climate.

Community 1.2
Mixed-grass

The Mixed-grass Savannah Community (1.2) is 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 abusive heavy 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 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 still 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. 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

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 Mixed-grass Savannah Community (1.2).

Pathway 1.2A
Community 1.2 to 1.1

Prescribed grazing, return of fire, and brush management will be necessary to transition back to the reference community (1.1).

State 2
Shrubland

Community 2.1
Shortgrass Mesquite/Mixed-Brush

The 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. 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

The Mesquite/Mixed-Brush Shortgrass Community (2.2) is dominated by mesquite and shrubs with few shortgrasses present. Remnants of the 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 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 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 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

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).

State 3
Reclamation

Community 3.1
Open Grassland

This community is the product of endeavors to reclaim the Shrubland State (2) back to a grassland. 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 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.

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 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 control brush effectively with fire. The Mixed-grass Savannah Community (1.2) then becomes the 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 T2A
State 2 to 3

Brush management is the primary driver for this transition. Once the woody species have been removed, range planting, return of natural fire intervals, and prescribed grazing are needed.

Transition T3A
State 3 to 2

Without brush management, prescribed fire, and prescribed grazing, the reclamation efforts will become covered in brushy species.