State 1
Reference

The reference state is considered to be representative of the natural range of variability under pre-Euro settlement conditions. This state was dominated by warm-season, deep-rooted, vegetation. Community phase changes are primarily driven by wildfire, grazing, and climatic fluctuations. The overstocking by cattle, sheep and goats in the late 1800s began a change in the plant composition of the Tallgrass Prairie Community towards a mixed-grass savannah with increasing woody species. As livestock numbers increased and grazing use exceeded the preferred plants' ability to sustain defoliation year after year, the most palatable species gave way to less palatable or more grazing resistant species. Because of selective grazing, the more palatable tall grasses decreased, giving way to secondary midgrass species.

Characteristics and indicators. The considerable precipitation (28 to 38 inches per year) comes primarily from convective storms during the warm season that favors deep-rooted vegetation. Deep-rooted trees and fire resistant shrubs, however, occupied only draws and ridges where they were protected from frequently occurring fires (Bray 1904 and Foster 1917). Recent studies conclude that before European settlement in the 1800s fires occurred at 7 to 12 year intervals in the Eastern Edwards Plateau region (Frost 1998). Without frequent and intense recurring fires, the Blackland Ecological Site would likely have been woodland.

Community 1.1
Tallgrass Prairie Community

The reference plant community for the Blackland Ecological Site was a tallgrass prairie composed of true prairie grassland vegetation that evolved under the influence of grazing, periodic fire and a humid subtropical climate. Woody plants, primarily live oak trees and mottes, were widely scattered on ridges and along draws. Shrubs such as sumac, elbowbush, ephedra (Ephedra spp.), algerita, bumelia (Sideroxylon lanuginosum) and prickly pear were likely present but were kept suppressed by periodic fires and grass competition. The grassland component accounted for 85 to 90 percent of the site’s primary annual production, with little bluestem accounting for 40 to 65 percent of the herbage production. Big bluestem and Indiangrass were confined to areas with deeper soils and were locally dominant. Secondary grasses were switchgrass (Panicum virgatum), sideoats grama, Arizona cottontop (Digitaria californica), feathery bluestems, tall dropseed (Sporobolus compositus var. compositus), Texas cupgrass (Eriochloa sericea) and Texas wintergrass. Shortgrasses like buffalograss and fall witchgrass (Digitaria cognata) were present in small amounts. Maximilian sunflower, Mexican sagewort (Artemesia ludoviciana), catclaw sensitivebriar (Mimosa aculeaticarpa var. biuncifera), bundleflower, western indigo (Indigofera miniata) and orange zexmenia (Wedelia acapulcensis var. hispida) were a few of the small (5-10 percent) but important forb component of the plant community (See Plant Community Composition and Annual Production table below). Soil erosion was low due to the abundant plant cover, litter, good soil structure and rapid infiltration. Runoff from the reference community was reduced due to grass cover and fissures in the limestone parent material. The vegetative ground cover helped disperse and slow down runoff thus holding soil in place and enhancing infiltration. Concentrated water flow patterns were rare. Without proper grazing management, that adjusts animal numbers, including deer, to annual forage production and judicious prescribed burning, the Tallgrass Prairie will transition (regress) to the Mixed-Grass Oak Savannah Plant Community (2).

Community 1.2
Mixed-Grass Oak Savannah Community

The Mixed-Grass Oak Savannah Community (2) is midgrass dominated grassland being encroached by indigenous or invading woody species that had been held at low densities by high frequency and intensity of fires and competition from a vigorous grass component. Numerous woody species, including juniper and mesquite, are increasing in density because heavy continuous grazing by livestock has reduced grass cover, exposed some soil and reduced fine fuel loads that are necessary for an effective fire. The woody canopy varies between 10 and 30 percent depending on severity of grazing, time since burned and availability of invading species. Typically, oaks increase in size and mesquite and/or juniper increase in density. Less preferred brush species such as bumelia, Texas persimmon (Diospyros texana), sumacs, condalia, elbowbush and feather dalea (Dalea spp.) also increase. The preferred tall grasses are being replaced by the more grazing resistant midgrasses. Characteristic grasses are little bluestem, sideoats grama, tall and meadow dropseed (Sporobolus asper var. asper), vine mesquite (Panicum obtusum), plains lovegrass (Eragrostis intermedia), Texas cupgrass and feathery bluestems. Most of the perennial forbs found in the historic climax remain in this plant community. In this phase, the increasing woody species are generally less than five feet tall and are subject to control by proper grazing management that allows effective prescribed burning. In the initial phase, individual plant treatments (IPT) may also be cost effective. Annual primary production ranges from 3,000 to 6,000 pounds per acre depending on precipitation amounts and soil series. Forage production is still predominantly from the grassland component. Heavy continuous grazing has reduced plant cover, litter and mulch and has increased bare ground exposing the soil to slight erosion. There could be some mulch and litter movement during rainstorms but due to gentle slopes and relatively good grass cover, little soil movement would take place in this vegetation type. The changes in species composition are small initially, but unless proper grazing and prescribed burning are applied the woody species continue to increase in size and density. As grazing continues, the tall and midgrasses give way to buffalograss and Texas wintergrass. When the canopy of the woody plants becomes dense enough (> 35 % canopy) and tall enough (> 5 feet height) to suppress grass growth and resist fire damage, a threshold in ecological succession is crossed. The Mixed-Grass Oak Savannah Community (2) transitions into the Oak/Mixed-Brush Community (3). Once this threshold is passed, normal range management practices, such as prescribed grazing and prescribed burning, cannot reverse the transition to woody plant dominance.

Pathway 1.1A
Community 1.1 to 1.2

Without proper grazing management that adjusts animal numbers, including deer, to annual forage production and judicious prescribed burning, the Tallgrass Prairie (1.1) will transition (regress) to the Mixed-Grass Oak Savannah Plant Community (1.2).

Pathway 1.2A
Community 1.2 to 1.1

In this phase, the increasing woody species are generally less than five feet tall and are subject to control by proper grazing management that allows effective prescribed burning. In the initial phase, individual plant treatments (IPT) may also be cost effective.

State 2
Encroached

This state is characterized by a shift in the dominant functional and structural groups. Understory is reduced due to shading from woody species (oak, mesquite and/or juniper). Cool-season, shortgrasses and annual and perennial forbs occupy the tree interspaces.

Community 2.1
Oak/Mixed-Brush Woodland Community

Figure 13. 3. Oak/Mixed-Brush Woodland Community

Oak, mesquite and/or juniper dominate the Oak/Mixed-Brush Woodland Community (3). Mesquite was the early understory brush species but Ashe juniper has increased tremendously in the past few decades. Common understory shrubs are pricklypear, algerita, condalia, yucca (Yucca spp.), Texas persimmon, elbowbush, pricklyash (Zanthoxylum spp.), and catclaw acacia (Acacia greggii). Shortgrasses, cool-season grasses and low quality annual and perennial forbs occupy the tree interspaces. Characteristic grasses found in this plant community are Texas wintergrass, curlymesquite, buffalograss and cedar sedge (Carex planostachys) initially. Representative forbs include dotted gayfeather (Liatris punctata var. punctata), orange zexmenia, croton (Croton spp.), western ragweed (Ambrosia psilostachya), prairie coneflower (Ratibida columnifera), snow-on-the-mountain (Euphorbia marginata) and broomweed (Gutierrezia spp.). With continued heavy grazing, either by livestock or deer, the brush canopy increases in density while shortgrasses, such as threeawns (Aristida spp.), red grama (Bouteloua trifida), Texas grama (Bouteloua rigidiseta), hairy tridens (Erioneuron pilosum) and cedar sedge replace the more palatable mid and short grasses. Grasses and forbs make up 25 percent or less of the annual herbage production. The tree and shrub canopy acts to intercept rainfall and increase evapotranspiration losses, creating a more xeric microclimate. Soil fauna and litter are reduced exposing more soil surface to erosion in the woody plant interspaces. Surface crusting is common where plant cover and soil conditions deteriorate in the grassland areas. However within the woody canopy, hydrologic processes stabilize and soil organic matter and mulch begin to increase and eventually stabilize under the mature woodland. Without major brush control and management inputs, this plant community cannot be reversed. The brush species will continue to thicken until the community stabilizes with the climate and soil. The oak/mixed-brush overstory can reach 80 to 90 percent ground cover with less than 25 percent of the herbage being produced by the weakened grassland component. With continued livestock grazing, the mature phase of the Oak/Mixed-Brush Woodland Community (3) provides cover for wildlife, but only limited preferred forage or browse is available for livestock or wildlife. Returning the Oak/Mixed-Brush Woodland Community (3) back to the grassland state requires extensive and expensive reclamation practices. Range planting, prescribed grazing and prescribed burning, must follow mechanical and/or chemical brush control. Land use other than livestock production might dictate alternative reclamation approaches to create the plant community that best fits the intended use.

State 3
Cropland State

Throughout MLRA 81C, many early settlers, having a farming background, cultivated small fields on the Blackland site for vegetable crops, grain, forage sorghum and winter cereals for livestock forage. Many of the Blackland sites have been converted to cropland in the past. Cropping of the site is still common for food and fiber production, livestock grazing, grain harvesting or planting for wildlife food plots on many ranches. Many fields, however, have been abandoned and let ‘go back’ to native rangeland or planted into introduced grasses for pastureland use.

Community 3.1
Cropland Community

Figure 16. 3. Cropland Community

Throughout MLRA 81C, many early settlers, having farming background, cultivated small fields on the Blackland site for vegetable crops, grain, forage sorghum and winter cereals for livestock forage. Many of the Blackland sites have been converted to cropland in the past. Cropping of the site is still common for food and fiber production, livestock grazing, grain harvesting or planting for wildlife food plots on many ranches. Many fields, however, have been abandoned and let ‘go back’ to native rangeland or planted into introduced grasses for pastureland use.

State 4
Pastureland State

Abandoned cropland areas, or cleared areas, are often seeded to native grass species or introduced grass species such as Kleingrass (Panicum coloratum), Gordo bluestem (Bothriochloa spp.) or bermudagrass (Cynodon spp.). Herbage production for adapted introduced grasses or native grasses can reach peak production within a few years after a full stand is established.

Community 4.1
Pastureland Community

Figure 20. 5. Pastureland Community

Abandoned cropland areas, or cleared areas, are often seeded to climax native grass species or introduced grass species such as Kleingrass (Panicum coloratum), Gordo bluestem (Bothriochloa spp.) or bermudagrass (Cynodon spp.). Herbage production for adapted introduced grasses or native grasses can reach peak production within a few years after a full stand is established. In this case, herbage production will equal the reference state if species such as big bluestem or Indiangrass are seeded. Adapted introduced species plantings such as bermudagrass may surpass reference production with the use of inputs. However, production may be dependent upon the degree of soil degradation, loss of structure and compaction. The practice of including adapted legumes or other forbs will enhance productivity and usefulness, especially for wildlife. Kept in a brush free condition with brush management, this plant community provides excellent forage for livestock and big game but poor cover habitat for big game. Invasion of pastureland by brush such as mesquite, huisache (Acacia smallii), baccharis (Baccharis spp.) and juniper is common in this MLRA. Drought and reduced soil cover due to cropping and grazing and a nearby seed source trigger the invasions. The shrub ‘seedlings’ that appear in seeded or abandoned fields are true seedlings established by seeds brought in by animals, water or wind. The invading brush must be controlled with grazing management, prescribed burning or other brush management methods or the woody invaders will again dominate.

State 5
Abandoned State

Go Back Land’ is a local name used to describe cropland fields that have been abandoned and are undergoing secondary succession. The plant community consists of a mixture of native grasses, forbs and shrubs. The ‘Go Back Land’ Community (6) results from abandoning cropland and leaving the land idle without implementing conservation practices such as range planting or brush management. Weeds and brush from the adjacent rangeland will invade the abandoned cropland. The initial invaders in abandoned fields on the Blackland site are annual, biennial and weak perennial grasses and forbs.

Community 5.1
Go Back Land Community

Figure 23. 5. Go Back Land Community

‘Go Back Land’ is a local name used to describe cropland fields that have been abandoned and are undergoing secondary succession. The plant community consists of a mixture of native grasses, forbs and shrubs. The ‘Go Back Land’ Community results from abandoning cropland and leaving the land idle without implementing conservation practices such as range planting or brush management. Weeds and brush from the adjacent rangeland will invade the abandoned cropland. The initial invaders in abandoned fields on the Blackland site are annual, biennial and weak perennial grasses and forbs. The species found on the site depends on the availability of seed sources from adjacent rangeland. The rate of succession depends on grazing management and drought frequency, but reestablishment of reference conditions can take many years. Biomass production will be limited in the early seral stage and may increase as the site recovers from cultivation. Without grazing management and brush management, brush species such as huisache, baccharis mesquite and juniper will dominate before a climax grass community can be established.

Transition T1A
State 1 to 2

The changes in species composition are small initially, but unless proper grazing and prescribed burning are applied the woody species continue to increase in size and density. As grazing continues, the tall and midgrasses give way to buffalograss and Texas wintergrass. When the canopy of the woody plants becomes dense enough (> 35 % canopy) and tall enough (> 5 feet height) to suppress grass growth and resist fire damage, a threshold in ecological succession is crossed. The Mixed-Grass Oak Savannah Community (1.2) transitions into the Oak/Mixed-Brush Community (2.1). Once this threshold is passed, normal range management practices, such as prescribed grazing and prescribed burning, cannot reverse the transition to woody plant dominance.

Transition T1B
State 1 to 3

Many early settlers, having a farming background, cultivated small fields on the Blackland site for vegetable crops, grain, forage sorghum and winter cereals for livestock forage. Many of the Blackland sites have been converted to cropland in the past. Cropping of the site is still common for food and fiber production, livestock grazing, grain harvesting or planting for wildlife food plots on many ranches.

Restoration pathway R2A
State 2 to 1

Returning the Oak/Mixed-Brush Woodland Community (2.1) back to the Grassland State (1.0) requires extensive and expensive reclamation practices. Range planting, prescribed grazing and prescribed burning, must follow mechanical and/or chemical brush control.

Transition T2B
State 2 to 3

Land use other than livestock production such as cropland might dictate alternative reclamation approaches to create the plant community that best fits the intended use. Cropland species such as small grains and forage annual crops are planted.

Transition T2A
State 2 to 4

Land use other than livestock production such as pastureland might dictate alternative reclamation approaches to create the plant community that best fits the intended use. Forage pasture species such as bermudagrass and kleingrass are planted.

Transition T3A
State 3 to 4

Cropping of the site is still common for food and fiber production, livestock grazing, grain harvesting or planting for wildlife food plots on many ranches. Many fields, however, have been planted into introduced grasses for pastureland use.

Transition T4A
State 4 to 3

Pastureland converted into cropland fields.

Transition T4B
State 4 to 5

Invasion of pastureland by brush such as mesquite, huisache (Acacia smallii), baccharis (Baccharis spp.) and juniper is common in this MLRA. Drought and reduced soil cover due to cropping and grazing and a nearby seed source trigger the invasions. The shrub ‘seedlings’ that appear in seeded or abandoned fields are true seedlings established by seeds brought in by animals, water or wind. The invading brush must be controlled with grazing management, prescribed burning or other brush management methods or the woody invaders will again dominate.

Transition T5A
State 5 to 2

In the absence of fire or brush management, abandoned fields may become dominated by woody species and resemble the woody state (2).