State 1
Grassland State

The interpretive or reference plant community for this site is a Tallgrass Prairie Community (1.1). This community is believed to have been a relatively open prairie with scattered motts of oak and an abundance of forbs. Little bluestem contributed from 20 to 25 percent of the herbage production. Indiangrass, switchgrass, sand bluestem, giant dropseed and purple tridens contributed 30 to 40 percent. Woody species included post oak, Havard oak, sand sagebrush, skunkbush, prickly-ash, bumelia and net-leaf hackberry. Woody plants are thought to have represented five to ten percent of the composition. The woody species were apparently kept at low levels because of frequent wildfires and occasional long droughts. Forbs such as Engelmann’s daisy, prairie clover, and dotted gayfeather thrived. It is estimated that the Tallgrass Prairie Community (1.1) produced as much as 5000 to 6000 pounds herbage in years with good moisture and as little as 3000 pounds to 4000 pounds in unfavorable years. The Mixed-Grass Plant Community (1.2) still have most reference species present but the dominant tallgrasses are being displaced by increases in silver bluestem, Arizona cottontop, sideoats grama, sand lovegrass and weeds. Of the tallgrasses, little bluestem is most persistent, often increasing initially under continued overgrazing before declining. Havard oak, sand sagebrush, skunkbush sumac, yucca, elbowbush and post oak increase in density and cover, varying from 15 to 25 percent canopy cover in this phase. Most climax forbs such as gaura, heath aster, dotted gayfeather, and verbena persist in the Mixed-grass Community. Annual yields range from 2500 to 5500 pounds.

Community 1.1
Tallgrass Prairie Community

The interpretive or reference plant community for this site is a Tallgrass Prairie Community (1.1). The reference plant community is believed to have been a relatively open prairie with scattered motts of oak and an abundance of forbs. Little bluestem contributed from 20 to 25 percent of the herbage production. Indiangrass, switchgrass, sand bluestem, giant dropseed and purple tridens contributed 30 to 40 percent. Woody species included post oak, Havard oak, sand sagebrush, skunkbush, prickly-ash, bumelia and net-leaf hackberry. Woody plants are thought to have represented five to ten percent of the composition. The woody species were apparently kept at low levels because of frequent wildfires and occasional long droughts. Forbs such as Engelmann’s daisy, prairie clover, dotted gayfeather, sagewort and verbena thrived in the sandy soils because of good soil moisture relationships. It is estimated that the Tallgrass Prairie Community (1.1) produced as much as 5000 to 6000 pounds herbage in years with good moisture and as little as 3000 pounds to 4000 pounds in unfavorable years. Grasses and forbs contributed up to 80 to 85 percent of the total annual production in reference conditions. The tallgrasses aided in the infiltration of rainfall and reduced runoff. Little runoff is thought to have occurred under normal rainfall conditions. Litter and organic matter buildup was limited by the dry climate, but ground cover is presumed to have been sufficient to prevent wind or water erosion under normal conditions. The Tallgrass Prairie Community (1.1) furnished good forage for grass-eating type animals such as bison before settlement and for horses and cattle after settlement. It was excellent habitat for deer, quail, dove, prairie chicken and other wildlife. Near reference grassland conditions can be maintained with proper stocking, prescribed grazing and frequent prescribed burning. The site is responsive to good management. Little bluestem is often persistent even under moderate grazing. Stocking rates must consider the kind of livestock and balance their numbers with current annual forage production and competition from other herbivores. Proper stocking and flexibility in animal numbers is important because of the nature of the soil and the need for plant cover to guard against wind erosion and water erosion on steeper slopes. Livestock overgrazing or a decrease in intensity and frequency of fires and no brush management will allow this plant community to transition into a Mixed-grass Community (1.2), which is relatively open grassland with various amounts of invading shrubs.

Community 1.2
Mixed-Grass Community

Figure 10. 1.2 Mixed-grass Community

The Mixed-grass Community (1.2) is the result of the interaction of long-term overgrazing, reduction in intensity and frequency of fires and possibly climate change (Milchunas 2006). The reduction in vegetative structure and ground cover resulting from continued overgrazing reduces the competitive advantage of grasses and allows increases in indigenous shrubs and invasion of less palatable shrubs, grasses and forbs from adjacent sites. Reduction in fire frequency and intensity allows the shrubs to become established. Continued overgrazing allows the less palatable grasses and forbs, or more grazing resistant species, to replace the more palatable tall and midgrasses. The composition of the Mixed-grass Community on this site varies with time and intensity of grazing. Most reference community species are present but the dominant tallgrasses are being displaced by increases in silver bluestem, Arizona cottontop, sideoats grama, sand lovegrass and weeds. Of the tallgrasses, little bluestem is most persistent, often increasing initially under continued overgrazing before declining. Havard oak, sand sagebrush, skunkbush sumac, yucca, elbowbush and post oak increase in density and cover, varying from 15 to 25 percent canopy cover in this phase. Litter and soil organic matter are lower than in climax condition and some wind or water erosion might occur. Most climax forbs such as gaura, heath aster, dotted gayfeather verbena, catclaw sensitivebriar, primrose and wild buckwheat persist in the Mixed-grass phase. Annual yields range from 2500 to 5500 pounds. Total herbage production is only slightly reduced, due primarily to fertility loss, but the proportionate production by woody species and unpalatable forbs increases as their percentage composition increases. The Mixed-grass Community on the Loamy Sand Prairie Ecological Site provides good grazing for grazers, such as cattle and excellent habitat for browsing animals, such as deer and goats. It can be maintained and retrogression reversed by proper grazing, minimal brush management and periodic prescribed burning. With continued overgrazing by livestock and no brush management, however, the shrub component matures and starts to dominate. Concurrently, shortgrasses and weeds continue to replace the tall and midgrasses. When woody plant cover reaches about 25 percent and/or the shrubs become resistant to fire this community transitions into a Shortgrass/Mixed-brush (2.1) Community. Once the Shortgrass/Mixed-brush (2.1) threshold is reached, grazing management and prescribed burning will generally not be effective in maintaining the community. More costly, accelerated brush control practices will be required to reverse the trend toward dense woodland.

Pathway 1.1A
Community 1.1 to 1.2

With Heavy Continuous Grazing, No Fires, Brush Invasion, and No Brush Management, the Tallgrass Prairie Community will shift to the Mixed-grass Community.

Pathway 1.2A
Community 1.2 to 1.1

With the implementation of various conservation practices such as Prescribed Grazing, Prescribed Burning, and Brush Management, the Mixed-grass Community can be shifted to the Tallgrass Prairie Community.

State 2
Woodland State

The Shortgrass/Mixed-brush Community (2.1) has a 25 to 45 percent woody plant canopy of Mixed-brush species. Post oak and/or mesquite are often becoming the dominant overstory and sand sagebrush or shin oak are the most common shrubs. The Mixed-brush/Shortgrass/Annuals Community on the Loamy Sand Prairie site is a woodland state. Sand sagebrush, yucca, and skunkbush sumac are common. Mesquite and sometimes post oak often become the dominant overstory. Sand sagebrush will often form dense stands. With continued heavy grazing and no brush control, the trees and shrubs can approach 75 percent or more ground cover. Shortgrasses and low seral stage annual and perennial forbs occupy the woody plant interspaces.

Community 2.1
Shortgrass/Mixed-brush Community

Figure 13. 2.1 Shortgrass/Mixed-brush Community

The Shortgrass/Mixed-brush Community (2.1) has a 25 to 45 percent woody plant canopy of Mixed-brush species. Post oak and/or mesquite are often becoming the dominant overstory and sand sagebrush or shin oak are the most common shrubs. The Shortgrass/Mixed-brush Community is the result of selective overgrazing by livestock and deer and the differential response of plants to defoliation over a long period of time. Fire frequency and intensity has also been reduced as a disturbance factor because of a paucity of fine fuel available and fire prevention. With or without livestock grazing, there is a continued decline in diversity of the grassland component and an increase in woody and annual species. Plant composition and production shifts toward the non-grass component as selective grazing reduces preferred species. Annual herbage production by the grassland component is reduced due to the shift to shorter species and less vigorous plants. There is a concomitant decline in soil structure, organic matter and ground cover. The site is susceptible to water or wind erosion. All, except the more palatable woody species, have increased in size and density. Many of the reference community shrubs are present. Typically, sand sagebrush plum, skunkbush sumac, pricklyash, shin oak and mesquite are increasing in density and frequency in this vegetation type. Remnants of historic climax grasses and forbs and unpalatable invaders occupy the interspaces between shrubs. Common grasses include fringed signalgrass, hooded windmillgrass, sand dropseed, sand paspalum, three-awns and many forbs. Little bluestem, giant dropseed, and sand lovegrass are often persistent. Western ragweed, woollywhite, prairie clover, dotted gayfeather, wild buckwheat and anemone are characteristic forbs. As the grassland vegetation declines, more soil is exposed leading to erosion on steeper slopes. The increasing woody canopy causes higher interception losses coupled with higher evaporation losses. Soil organic matter and soil structure decline within the interspaces but soil conditions improve under the woody plant cover. Wind blowouts are infrequent but do occur in bare areas. Total plant production declines somewhat, being approximately 2000 to 4500 pounds per acre, depending on precipitation. The deeper rooting shrubs are able to increase vegetative growth if erosion has not depleted the soil. Generally, only about 50 percent of annual production comes from the grass component. Browsing animals such as goats and deer can find fair food value, if browse plants have not been overgrazed continuously. Forage quantity and quality for cattle is low. Unless brush management and good grazing management are applied at this stage, the transition toward the Mixed-Brush/Shortgrass/Annuals Community (2.2) will continue. The trend cannot be reversed with good grazing management alone. Woody species will eventually dominate the site.

Community 2.2
Mixed-brush/Shortgrass/Annuals Community

Figure 16. 2.2 Mixed-brush/Shortgrass/Annuals Community

The Mixed-brush/Shortgrass/Annuals Community on the Loamy Sand Prairie site is a shrubland resulting from many years of overgrazing, lack of periodic fires and little brush management. Sand sagebrush, yucca, skunkbush sumac, pricklyash and sand plums are common. Mesquite and sometimes post oak often become the dominant overstory. Sand sagebrush will often form dense stands. With continued heavy grazing and no brush control, the trees and shrubs can approach 75 percent or more ground cover. Shortgrasses and low seral stage annual and perennial forbs occupy the woody plant interspaces. Characteristic grasses are hooded windmillgrass, tumble windmillgrass, gummy lovegrass, fall witchgrass, fringed paspalum, sand paspalum and sand dropseed. Forbs commonly found in this community include camphorweed, prairie clover, verbena, astragalus, heath aster, wollywhite wildbean and anemone. Numerous annual grasses and forbs may be present. Grasses and forbs make up 30 percent or less of the annual herbage production. The Mixed-brush/Shortgrass/Annuals Community provides good cover for wildlife, but only limited preferred forage, or browse. Major high cost and high energy, accelerating practices are required to restore the Mixed-brush/Shortgrass/Annuals Community (2.2) back to a grassland state. Generally, brush management practices such as aerial herbicide application, along with other conservation practices such as range planting, grazing deferment, prescribed grazing and prescribed burning are necessary to return the shrubland state the grassland state. In practice this may not be practical or desirable depending on objectives of the land manager.

Pathway 2.1A
Community 2.1 to 2.2

Shortgrass/Mixed-brush Community

Mixed-brush/Shortgrass/Annuals Community

With heavy continuous grazing, no fire, and no brush management, the Shortgrass/Mixed-brush Community will shift to the Mixed-brush/Shortgrass/Annuals Community.

Pathway 2.2A
Community 2.2 to 2.1

Mixed-brush/Shortgrass/Annuals Community

Shortgrass/Mixed-brush Community

With Brush Management and Prescribed Grazing, the Mixed-brush/Shortgrass/Annuals can shift back to the Shortgrass/Mixed-brush Community.

State 3
Converted Land State

Community 3.1
Converted Land Community

The Loamy Sand Prairie Ecological Site is planted into the Converted Land Community (3.1) and planted to crops or pasture grasses. Technical advice as to adapted crops, cropping systems, production, and cultivation practices are available from local NRCS or Extension Service offices. When abandoned from cropping, the site should be re-vegetated with adapted native plant mixtures, which include historic climax species. Cultivation and erosion may have reduced soil productivity but near historic forage production may be obtained with a native plant mix that approximates reference community specie composition. Introduced species often require more care, but can also be productive as pasture. In any case brush management is required to prevent brush invasion from adjacent areas. If fields are abandoned and left to re-vegetate naturally, weedy grasses, forbs and shrubs will be the first species in secondary succession. Even without grazing, woody species will encroach and eventually dominate unless brush management practices such as individual plant treatments (IPT) and prescribed burning are applied.

Transition T1A
State 1 to 2

With continued overgrazing by livestock and no brush management, however, the shrub component matures and starts to dominate. Concurrently, shortgrasses and weeds continue to replace the tall and midgrasses. When woody canopy cover reaches about 25 percent and/or the shrubs become resistant to fire, the Grassland State transitions into the Woodland State.

Transition T1B
State 1 to 3

The transition to the Converted Land State occurs when crop cultivation practices, plowing, range planting, pasture planting, pest management, and nutrient management are applied to cropland, pastureland or go back land.

Restoration pathway R2A
State 2 to 1

Converting the Woodland State back to the Grassland state requires extensive and expensive reclamation practices. Without major brush control and management inputs, this plant community cannot be returned to grassland. Range planting, prescribed grazing and prescribed burning, must follow intensive mechanical brush control.

Transition T2A
State 2 to 3

The transition to the Converted Land State occurs when crop cultivation practices, plowing, range planting, pasture planting, pest management, and nutrient management are applied to cropland, pastureland or go back land.