State 1
Prairie State - Reference

Community 1.1
Tallgrass Prairie Community

Figure 9. 1.1 Tallgrass Prairie Community

The Tallgrass Prairie Community (1.1) is the reference community. It is characterized by moderately deep to deep, neutral to calcareous, stony or very stony, clay loams, silty clay loams, or loams. The soils are fertile and can store large amounts of water. Limestone fragments and rocks cover 5 to 20 percent of the soil surface, but do not inhibit plant growth. This site is dominated by warm-season, perennial tallgrasses, with warm-season, perennial midgrasses filling most of the remaining species composition. The warm-season, perennial forb component varies between 5 and 15 percent depending on climatic patterns and local precipitation. Woody species make up a minor component of the community, typically 2 percent or less.

Indiangrass dominates the site. Indiangrass, little bluestem and big bluestem act as decreasers on this site and are the first species to be removed by improper grazing management. Important midgrasses include sideoats grama (Bouteloua curtipendula), meadow dropseed (Sporobolus compositus), silver bluestem (Bothriochloa laguroides), and Texas wintergrass. Forbs commonly found on the site include: Maximilian sunflower (Helianthus maximiliani), Engelmann daisy (Engelmannia peristenia), blacksamson (Echinacea angustifolia), scurfpea (Psoralidium), halfshrub sundrop (Calylophus serrulatus), sensitive-briar (Mimosa spp.), and yellow neptunia (Neptunia lutea). Tree species are limited to scattered live oaks which may grow in small mottes.

The reference grassland community will transition to a midgrass-dominated community under the stresses of improper grazing management. The first species to decrease in dominance will be the most palatable and/or least grazing tolerant grasses and forbs (e.g., Indiangrass, big bluestem, and Engelmann daisy). If improper grazing management continues, little bluestem will decrease and midgrasses such as silver bluestem and sideoats grama will increase in composition. Forbs, particularly less palatable species, will increase at this stage. This site can have dramatic increases in forbs, particularly following a fire.

This plant community has very little bare ground. Plant basal cover, litter, and rock fragments make up almost 100 percent ground cover. Infiltration and runoff are moderate. Soils are high in organic matter and the heavy plant cover contributes to increasing organic matter and soil building.

Community 1.2
Midgrass Prairie Community

Figure 12. 1.2 Midgrass Prairie Community

The Midgrass Community Phase (1.2) is the result of improper cattle grazing management over a long period of time. Tallgrasses decrease in vigor and production, allowing midgrasses, shortgrasses and forbs to increase to the point that they make up more than 50 percent of species composition. Woody species may begin to encroach from adjacent sites depending on fire and brush control methods.

Important grasses include: little bluestem, silver bluestem, sideoats grama, hairy grama, dropseeds, buffalograss, Texas wintergrass, and tridens species. Some of the perennial forbs persist, but less palatable forbs will increase. Forbs can increase to as high as 40 percent in this community, particularly following fire. Invasive shrub species encroach when overgrazing by livestock has reduced grass cover, exposed more soil, and reduced grass fuel for fire. Typical invaders include honey mesquite (Prosopis glandulosa) and juniper (Juniperus ashei).

Aggressive, introduced grasses such as King Ranch bluestem (Bothriochloa ischaemum) may begin to invade the Midgrass Plant Community, particularly if they have been seeded in nearby pastures or fed in hay.

Heavy continuous grazing will reduce plant cover, litter, and mulch. Bare ground will increase and expose the soil to crusting and erosion. Some mulch and litter movement may occur during rainstorms, but little soil movement occurs due to gentle slopes in this vegetation type. Litter and mulch will move off site as plant cover declines. Increasing woody species include honey mesquite, juniper, and lotebush. Once shrubs reach a height of about 3 feet, they become more resistant to being killed by fires.

If improper grazing management continues Midgrass Plant Community will transition (1.2B) to the Shortgrass/Midgrass Prairie State. Tallgrasses will disappear and late successional midgrasses will decline noticeably. Grazing-resistant shortgrasses, early successional midgrasses, unpalatable forbs and annuals will become the representative plant community.

Pathway 1.1A
Community 1.1 to 1.2

Tallgrass Prairie Community

Midgrass Prairie Community

The Tallgrass Prairie State is comprised of two plant communities. The Tallgrass Prairie Community (1.1) will shift to the Midgrass Prairie Community (1.2) when there is continued growing season stress on the palatable tallgrass species. These stresses include excessive stocking rates, insufficient critical growing season deferment, excess defoliation intensity, repeated long-term growing season defoliation, and/or long-term drought. Increaser species (midgrasses, shortgrasses, and forbs) are frequently endemic species released from tallgrass competition. Woody species canopy is a very small part of the reference community (scattered trees or mottes making up less than 5% canopy cover). Dominance of tallgrasses falling below 50% of species composition indicates a transition to the Midgrass Prairie Community. The reference community can be maintained through the implementation of managed grazing that includes proper stocking rates, adequate growing season deferment to allow establishment of tallgrass propagules and/or the recovery of the vigor of stressed individual plants. Proper grazing management may be combined with fire to create a shift towards, or maintain the reference plant community. The driver for community shift 1.1A for the herbaceous component is improper grazing management.

Pathway 1.2A
Community 1.2 to 1.1

Midgrass Prairie Community

Tallgrass Prairie Community

The Midgrass Prairie Community (1.2) will return to the Tallgrass Prairie Community (1.1) under grazing management that includes proper stocking rates and sufficient critical growing season deferment in combination with proper grazing intensity. Favorable moisture conditions will facilitate or accelerate this transition. The understory component may return to dominance by tallgrasses in the absence of fire. The driver for community shift 1.2A for the herbaceous component is proper grazing management.

State 2
Shortgrass/Midgrass State

Community 2.1
Shortgrass/Midgrass Community

Figure 15. 2.1 Shortgrass/Midgrass Community

The Shortgrass/Midgrass Community (2.1) exists as a result of long-term abusive grazing and/or extended severe drought conditions.

Sideoats grama and other late successional midgrasses decrease significantly and are replaced by shortgrasses and early successional midgrasses such as buffalograss (Bouteloua dactyloides), dropseeds (Sporobolus spp.), tumble windmillgrass (Chloris verticillata), tumblegrass (Schedonnardus paniculatus), Texas grama (Bouteloua rigidiseta), threeawns (Aristida spp.), annuals, western ragweed (Ambrosia psilostachya), and broomweed (Amphiachyris dracunculoides). Plant vigor and productivity of the grassland component is reduced due to competition for sunlight, nutrients, and water from “weedy” species. As the grassland vegetation declines, more soil is exposed, leading to crusting and erosion.

State 3
Mixed-brush State

Community 3.1
Mixed Brush Community

Figure 18. 3.1 Mixed Brush Community

The Mixed-Brush Community (3.1) has 15-30 percent woody canopy cover and is the result of many years of improper grazing, lack of periodic fires, and/or a lack of proper brush management. Invading woody species such as honey mesquite and juniper dominate the Mixed Brush Community (3.1). The site can now have the appearance of a shrubland interspersed with open grassland areas. Common understory shrubs are pricklypear (Opuntia spp.), lotebush (Ziziphus obtusifolia), yucca (Yucca spp.), and sumac (Rhus spp.).

Remnant midgrasses and opportunistic shortgrasses, annuals, and perennial forbs dominate the site. Texas wintergrass, sedges, and annuals are found in and around tree/shrub cover. Grasses and forbs make up 50 percent or less of the annual herbage production. Common forbs include dotted gayfeather, croton, western ragweed, verbena (Verbena spp.), snow-on-the-prairie (Euphorbia bicolor), Mexican sagewort (Artemisia ludoviciana ssp. mexicana), and sensitive-briar.

The shrub canopy acts to intercept rainfall and increase evapotranspiration losses, creating a more xeric microclimate. Soil fauna and organic mulch are reduced, exposing more of the soil surface to erosion in interspaces. The exposed soil crusts readily. However, within the woody canopy, hydrologic processes stabilize and soil organic matter and mulch begin to increase and eventually stabilize under the shrub canopy.

The Mixed Brush Community (3.1) can provide good cover habitat for wildlife, but only limited forage or browse is available for livestock or wildlife. At this stage, highly intensive restoration practices are needed to return the brushy community to grassland. Alternatives for restoration include: brush management and range planting, with proper stocking; prescribed grazing; and prescribed burning following restoration to maintain the desired community.

Excessive cattle grazing tends to create a different response and structure to the community than does excessive deer or goat grazing. Excessive cattle grazing tends to accelerate invasion of shrubs because it creates conditions where young shrubs increase in vigor and size while palatable grasses decrease in vigor and abundance. Excess deer or goat grazing tends to create a dominance of large trees by removing both young shrubs and the young growth that grow below the browse line on larger shrubs and trees. While large trees will continue to increase in size, they will have very little production below the browse line. The site becomes dominated by large trees with little forage available for livestock or wildlife. Large trees with little understory provide much less soil protection than do dense stands of grass. As soils erode, understory species have reduced potential to revegetate the site. The bare area under the browse line creates a situation that provides poor forage conditions and poor visual cover for wildlife.

If irreversible soil damage has occurred, it may be possible to remove brush and seed the site to a grassland community. The resulting grassland will not look or function like the reference community (1.1). Instead, it is likely to be dominated by few introduced midgrasses and produce less biomass than the community 1.1. However, it is very difficult and expensive to restore the site to reference (1.1) conditions due to the loss of organic matter, soil horizons, soil microbes, and soil structure necessary to maintain the reference community (1.1). Rangeland health functions will depart substantially from reference (1.1) conditions.

Transition T1A
State 1 to 2

Excessive grazing and/or extended severe drought will eventually result in almost complete loss of the tallgrass and a severe decline of higher successional midgrass species on this site. They are replaced by shortgrasses, lower successional midgrasses, less palatable forbs, and annuals. The driver for transition T1A for the herbaceous component is improper grazing management.

Transition T1B
State 1 to 3

The grassland states and plant communities are resistant to shrub dominance. However, shrubs are present in minor amounts in those states and communities, therefore propagules are present. Even with proper grazing and favorable climate conditions, lack of fire or brush control for over 25 years will allow woody species to encroach from adjacent sites and allow endemic woody species to increase in canopy to reach the 30% threshold level. Once canopy cover reaches 15% the transition to the mixed brush state has begun. Canopy cover of 30% indicates that the transition has occurred. Improper grazing management, prolonged drought, and a warming climate will provide a competitive advantage to shrubs which will accelerate this process. This transition can occur from any of the grassland states and plant communities. The drivers for this transition are excessive grazing as well as lack of fire and/or brush control. Introduction of aggressive woody invader species (i.e. mesquite or juniper) increase the risk that this state transition will occur and accelerate the rate at which it is likely to occur. The driver for this transition is lack of fire and/or brush control.

Restoration pathway R2A
State 2 to 1

The Shortgrass/Midgrass State will require range planting accompanied by return to the proper grazing management that includes proper stocking rates and sufficient critical growing season deferment in combination with proper grazing intensity in order to return to the Tallgrass State. Favorable moisture conditions will facilitate or accelerate this transition. The driver for the herbaceous component is proper grazing management.

Transition T2A
State 2 to 3

The grassland states and plant communities are resistant to shrub dominance. However, shrubs are present in minor amounts in those states and communities, therefore propagules are present. Even with proper grazing and favorable climate conditions, lack of fire or brush control for over 25 years will allow woody species to encroach from adjacent sites and allow endemic woody species to increase in canopy to reach the 30% threshold level. Once canopy cover reaches 15% the transition to the mixed brush state has begun. Canopy cover of 30% indicates that the transition has occurred. Improper grazing management, prolonged drought, and a warming climate will provide a competitive advantage to shrubs which will accelerate this process. This transition can occur from any of the grassland states and plant communities. The drivers for this transition are excessive grazing as well as lack of fire and/or brush control. Introduction of aggressive woody invader species (i.e. mesquite or juniper) increase the risk that this state transition will occur and accelerate the rate at which it is likely to occur. The driver for this transition is improper grazing management as well as lack of fire and/or brush control. A system of brush management and fire can reduce the woody component below the transition level of 30% canopy. Managers may chose to leave some brush for wildlife habitat objectives. Continued fire and/or brush management will be required to maintain woody density and canopy below the threshold. If the herbaceous component has transitioned to shortgrasses and low forbs, proper grazing management (combined with favorable moisture conditions and adequate seed source) will be necessary to facilitate the shift of the understory component to a midgrass-dominated plant community. Range planting may accelerate the transition of the herbaceous community, particularly when combined with favorable growing conditions.

Restoration pathway R3A
State 3 to 1

Restoration of the Mixed Brush State to the Tallgrass Prairie State requires substantial energy input. Mechanical or chemical brush control treatments can be used to remove woody species. A long-term prescribed fire program may sufficiently reduce brush density to a level below the threshold of the Mixed Brush State, particularly if the woody component is dominated by species that are not re-sprouters. However, fire may not be sufficient to remove mature trees. A mixed program consisting of mechanical, chemical, and fire measures may be used. Brush control in combination with prescribed fire, proper grazing management, and favorable growing conditions may be the most economical means of creating and maintaining the desired plant community. If remnant populations of tallgrasses, midgrasses, and desirable forbs are not present at sufficient levels, range planting will be necessary to restore the reference plant community. Depending on the understory community and inputs of seed, the restoration pathway can result in a return to any of the Grassland State Communities. The driver for Restoration Pathway R3A is fire and/or brush control combined with restoration of the herbaceous community and proper grazing management. Restoration may require aggressive treatment of invader species.

Restoration pathway R3B
State 3 to 2

Restoration of the Mixed Brush State to the Shortgrass/Midgrass Prairie State requires substantial energy input. Mechanical or herbicidal brush control treatments can be used to remove woody species. A long-term prescribed fire program may sufficiently reduce brush density to a level below the threshold of the Mixed Brush State, particularly if the woody component is dominated by species that are not re-sprouters. However, fire may not be sufficient to remove mature trees. A mixed program consisting of mechanical, chemical, and fire measures may be used. Brush control in combination with prescribed fire, proper grazing management, and favorable growing conditions may be the most economical means of creating and maintaining the desired plant community. The driver for Restoration Pathway R3B is fire and/or brush control combined with restoration of the herbaceous community and proper grazing management. Restoration may require aggressive treatment of invader species.