State 1
Grassland State

The Grassland State defines the ecological potential and natural range of variability resulting from the natural disturbance regime of the Subirrigated ecological site. This state is supported by empirical data, historical data, local expertise, and photographs.

Characteristics and indicators. The Grassland State is defined by a suite of native plant communities that are the result of periodic fire, drought, and grazing. These events are part of the natural disturbance regime and climatic process. The Reference Plant Community consists of warm-season tall- and midgrasses, cool-season and sod-forming grasses, forbs, and shrubs. The Tallgrass/Midgrass Plant Community is made up primarily of warm-season tallgrasses with midgrasses, sedges, and rushes as a subdominant component and decreasing amounts of forbs. The Midgrass Plant Community is dominated by less desirable midgrasses, while shortgrasses, forbs, sedges, rushes, and tallgrasses are sudominant.

Resilience management. Management that includes a forage and animal balance and a prescribed burning program should sustain the Grassland State and prevent a transition.

Community 1.1
Reference Plant Community

Figure 9. MLRA 74 Reference Plant Community.

The interpretive plant community for the Subirrigated ecological site is the Reference Plant Community. It represents the original plant community that existed prior to European settlement. The site is characterized as a grassland essentially free of trees and large shrubs. It is dominated by tall warm-season grasses including big bluestem, Indiangrass, switchgrass, eastern gamagrass, and prairie cordgrass. Another tall grass, common reed, is occasionally found on the site. It generally forms large colonies on deep sandy alluviums adjacent to streams. Combined, these tall grasses will account for 75 to 85 percent of the total vegetation produced annually. Other prevalent grasses and grasslike plants are Canada wildrye, Virginia wildrye, western wheatgrass, little bluestem, marsh bristlegrass, composite dropseed, and several species of sedges and rushes. The two major forbs found interspersed throughout the grass sward are Maximilian sunflower and prairie bundleflower. Other important forbs include Canada goldenrod, pitcher sage, white heath aster, white sagebrush, American licorice, roundhead lespedeza, and white prairie clover. Desert false indigo, common buttonbush, and roughleaf dogwood are shrubs that occur in sparse amounts over the site. Eastern cottonwood and black willow are the major trees. Eastern cottonwood may be found as isolated plants scattered over the site or it may form small groves. Black willow is generally located along drainageways. In a number of locations this plant community is managed exclusively for hay production. Mowing tends to reduce the amount of switchgrass and prairie cordgrass plants and favor big bluestem, Indiangrass, and eastern gamagrass.

Resilience management. This is a stable, resilient, and very productive plant community when adequately managed. A prescribed grazing program that incorporates periods of rest and recovery during the growing season perpetuates the more palatable tall grasses and forb species.

Community 1.2
Tallgrass/Midgrass Plant Community

Figure 12. MLRA 74 Tallgrass-Midgrass Plant Community.

The composition of the Tallgrass-Midgrass Plant Community is dominated by a mixture of tallgrasses and midgrasses. Compared with the Reference Plant Community, there has been a decrease of the more palatable tallgrasses and forbs and a subsequent increase in less palatable and lower-producing midgrasses. Although reduced by overgrazing, tall grasses such as big bluestem, Indiangrass, switchgrass, and prairie cordgrass remain the dominant plants in this community. However, the proportion of midgrasses, sedges, and rushes in the overall production of the site has increased. These include composite dropseed, little bluestem, western wheatgrass, marsh bristlegrass, Torrey’s rush, and threesquare. Other secondary grasses that have increased are Texas bluegrass, alkali sacaton, vine mesquite, and sedges. Combined, secondary plants now comprise 30 to 40 percent of the total annual production. Forbs (Maximilian sunflower and prairie bundleflower) have decreased and have largely been replaced by white heath aster, white sagebrush, Cuman ragweed, Baldwin's ironweed, and Canada goldenrod. Forbs account for 8 to 10 percent of the annual production. In some locations the site supports an increasing amount of shrubs and trees. The most abundant shrubs are desert false indigo, common buttonbush, rough leaf dogwood, Great Plains false willow, and coralberry. Eastern cottonwood, black willow, American elm, and Russian olive (Elaeagnus angustifolia) are the major trees found on the site. Shrubs and trees usually will not comprise over 5 percent of the total production.

Resilience management. Planned periods of deferment from grazing during the growing season are important in maintaining the vigor and production of some of the major grasses found in this plant community. Eastern gamagrass and big bluestem are especially preferred and selectively grazed by cattle. When the site is grazed continuously throughout the growing season, these grasses are usually overgrazed and thus maintained in a lower state of plant vigor. Continued for many years, overgrazing will result in a gradual reduction of these grasses. Prescribed grazing that incorporates periods of deferment during the growing season will improve the vigor and gradual recovery of the more palatable tall grasses and forbs.

Community 1.3
Midgrass/Shortgrass Plant Community

Figure 13. MLRA 74 Midgrass-Shortgrass Plant Community.

The Midgrass-Shortgrass Plant Community results from many years of overgrazing. The amount of tallgrasses has decreased significantly and the site is dominated by midgrasses and shortgrasses. Major midgrasses are composite dropseed, Madagascar dropseed, vine mesquite, silver beardgrass, sideoats grama, western wheatgrass, and marsh bristlegrass. Shortgrasses include Kentucky bluegrass, Texas bluegrass, Texas dropseed, buffalograss, blue grama, Carolina crabgrass, and inland saltgrass. Grasslike plants such as chairmaker’s threesquare, Baltic rush, Torrey’s rush, and sedges have increased and may comprise 10 to 20 percent of the plant community in some locations. Major forbs on the site are Cuman ragweed, Canada goldenrod, Missouri goldenrod, white sagebrush, Carruth’s sagewort, white heath aster, swamp smartweed, swamp milkweed, swamp verbena, annual marshelder, and annual ragweed. In some locations the Subirrigated site supports an increasing amount of shrubs and trees. The most abundant shrubs are desert false indigo, common buttonbush, rough leaf dogwood, Great Plains false willow, and coralberry. Saltcedar (Tamarix ramosissima) may occur on soils with moderate salinity. Eastern cottonwood, black willow, peachleaf willow, American elm, eastern redcedar (Juniperus virginiana), and Russian olive are the major trees found on the site. Both eastern redcedar and Russian olive were introduced to the area through shelterbelt and windbreak plantings and have spread onto the site. Shrubs and trees usually will not comprise over ten percent of the total production. Remnant plants of big bluestem, Indiangrass, switchgrass, prairie cordgrass, eastern gamagrass, and Maximilian sunflower are often found scattered throughout the site. These plants are usually grazed repeatedly and maintained in a low state of vigor. These remnants respond favorably to periods of rest from grazing during the growing season and often regain vigor in one to two years.

Resilience management. Remnant plants of big bluestem, Indiangrass, switchgrass, prairie cordgrass, eastern gamagrass, and Maximilian sunflower are often found scattered throughout the site. These plants are usually grazed repeatedly and maintained in a low state of vigor. They respond favorably to periods of rest from grazing during the growing season and often regain vigor in one to two years.

Pathway 1.1 to 1.2
Community 1.1 to 1.2

Reference Plant Community

Tallgrass/Midgrass Plant Community

The following describes the mechanisms of change from Plant Community 1.1 to Plant Community 1.2. These mechanisms include management controlled by repetitive heavy use, no rest or recovery of the key forage species, and no forage and animal balance for many extended grazing seasons. This type of management for periods greater than 10 years will shift functional and structural plant group dominance toward Plant Community 1.2.

Pathway 1.2 to 1.1
Community 1.2 to 1.1

Tallgrass/Midgrass Plant Community

Reference Plant Community

The following describes the mechanisms of change from Plant Community 1.2 to Plant Community 1.1. Management (10-15 years) that includes adequate rest and recovery of the key forage species (big bluestem, Indiangrass, and switchgrass) within the Reference Plant Community. If woody species are present, prescription fires every 6-8 years will be necessary for their removal and maintenance.

Pathway 1.2 to 1.3
Community 1.2 to 1.3

Tallgrass/Midgrass Plant Community

Midgrass/Shortgrass Plant Community

These mechanisms include management controlled by repetitive heavy use, no rest or recovery of the key forage species, and no forage and animal balance for many extended grazing seasons. This type of management lasting for periods greater than 20 years will shift functional and structural plant group dominance toward a Midgrass-Shortgrass Plant Community.

Pathway 1.3 to 1.2
Community 1.3 to 1.2

Midgrass/Shortgrass Plant Community

Tallgrass/Midgrass Plant Community

Causes of plant community shift include management (10-15 years) with adequate rest and recovery of the key forage species (little bluestem, sideoats grama, big bluestem, switchgrass, and Indiangrass) within the Tallgrass/Midgrass Plant Community. If woody species are present, prescription fires every 6-8 years will be necessary for their removal and maintenance.

State 2
Woody State

The Woody State is dominated by a shrub and/or tree plant community.

Characteristics and indicators. The increase and spread of shrubs and trees results from an absence of fire. Woody plants can increase up to 34 percent from a lack of fire according to a study from 1937 to 1969, in contrast to a 1 percent increase on burned areas (Bragg and Hulbert, 1976). Periodic burning tends to hinder the establishment of most woody species and favors forbs and grasses. However, it should be pointed out that not all unburned areas have a woody plant invasion. Hydrologic function is affected by the amount of vegetative cover. Canopy interception loss can vary from 25.4 percent to 36.7 percent (Thurow and Hester, 1997). A small rainfall event is usually retained in the foliage and does not reach the litter layer at the base of the tree. Only when canopy storage is reached and exceeded does precipitation fall to the soil surface. Interception losses associated with the accumulation of leaves, twigs, and branches at the base of trees are considerably higher than losses associated with the canopy. The decomposed material retains approximately 40 percent of the water that is not retained in the canopy (Thurow and Hester, 1997). Soil properties affected include biological activity, infiltration rates, and soil fertility. Special planning will be necessary to assure that sufficient amounts of fine fuel are available to carry fires with enough intensity to control woody species. In some locations the use of chemicals as a brush management tool may be desirable to initiate and accelerate this transition. Birds, small mammals, and livestock are instrumental in the distribution of seed and accelerating the spread of most tree and shrubs common to this site. The speed of encroachment varies considerably and can occur on both grazed and non-grazed pastures. Many species of wildlife, especially bobwhite quail, turkey, and white-tailed deer benefit from the growth of trees and shrubs for both food and cover. When management for specific wildlife populations is desirable, these options should be considered in any brush management plan.

Resilience management. This Woody State is sustained by a lack of fire and brush management.

Community 2.1
Tree/Shrub Community

Trees and shrubs dominate this plant community and may produce 40 to 50 percent of the total vegetation. Major trees include eastern cottonwood, black willow, peachleaf willow, American elm, Siberian elm (Ulmus pumila), common hackberry (Celtis occidentalis), eastern redcedar, and Russian olive. More abundant shrubs are roughleaf dogwood, coralberry, Great Plains false willow, desert false indigo, and common buttonbush. Saltcedar has invaded and become well established in some locations, especially where soils are moderately saline. The spread of these woody plants results in the absence of fire and may occur on the site regardless of grazing management. However, not all unburned areas have a woody plant problem. Encroachment may occur on areas that have been overgrazed for years as well as on areas where both grazing and fire have been excluded. The speed and method of encroachment varies considerably. Cottonwood and willow produce an abundance of seed that is distributed long distances by the wind. Russian olive and eastern redcedar are spread by birds. Periodic burning tends to hinder the establishment of most of these woody species and favor forb and grass species. Where woody plants have invaded overgrazed areas, understory vegetation is generally dominated by plants such as Texas bluegrass, Kentucky bluegrass, composite dropseed, marsh bristlegrass, chairmaker’s threesquare, sedges, white sagebrush, swamp verbena, Baldwin's ironweed, and white heath aster. Where woody plants have encroached onto nonutilized areas, the understory consists largely of big bluestem, Indiangrass, prairie cordgrass, Canada wildrye, chairmaker’s threesquare, sedges, prairie bundleflower, and Maximilian sunflower. Herbage production is significantly reduced because of the tree and shrub competition. Grass yields vary from 30 to 40 percent of the total vegetative production. Forbs generally produce 5 to 10 percent of the total.

Resilience management. Usually a prescribed burning program, accompanied by prescribed grazing, will return the plant community to one dominated by grasses and forbs. Special planning will be necessary to assure that sufficient amounts of fine fuel are available to carry fires with enough intensity to control the woody species. In some locations use of chemicals or mechanical methods as a brush management tools may be necessary to initiate and accelerate this transition.

State 3
Tillage State

The Tillage State consists of abandoned cropland that has been naturally revegetated ("go-back") or seeded to grassland.

Characteristics and indicators. Many reseeded plant communities were planted with a local seeding mix under the Conservation Reserve Program (CRP), or were planted to a monoculture of sideoats grama or other species. Go-back communities are difficult to define due to the variability of plant communities that can exist. Many of these communities are represented by the genus Aristida (threeawns). This is an alternative state since the energy, hydrologic, and nutrient cycles are altered to that of the Reference State in its natural disturbance regime. Bulk density, aggregate stability, soil structure, and plant functional and structural groups are not fully restored to that of the Reference State. Mechanical tillage can destroy soil aggregation. Soil aggregates are an example of dynamic soil property change. Aggregate stability is critical for infiltration, root growth, and resistance to water and wind erosion (Brady and Weil, 2008).

Resilience management. This state should incorporate prescribed grazing and prescribed burning management strategies.

Community 3.1
Reseed Community

The Reseed Plant Community occurs on areas that were formerly farmed. When farming operations ended, the area was seeded and established to a mixture of plants. These were usually native species common in the Reference Plant Community. Most seeding mixtures consisted of a blend of grasses that included big bluestem, Indiangrass, switchgrass, and little bluestem. In some locations seed of additional plants such as eastern gamagrass, prairie bundleflower, and Maximilian sunflower were included in the mixture. When reseeded areas and areas supporting native rangeland exist in the same pasture, they seldom are utilized at the same intensity. There is usually a preference by domestic livestock for the plants on the native rangeland areas. When feasible, reseeded plant communities should be managed as separate pastures or units. These areas are generally productive when managed for hay production. Some seeded areas are invaded by trees and shrubs during the establishment period of the desired plants. These invader species commonly include Siberian elm, common hackberry, eastern redcedar, eastern cottonwood, black willow, roughleaf dogwood, and Great Plains false willow. Occasional burning is effective in controlling the establishment of these woody plants. Once seeded areas become fully established, production is comparable to that of the Reference Plant Community. Total annual production is variable. Sufficient data does not exist to give estimates at this time.

Resilience management. Following termination of cultivation, total annual production is quite variable and full recovery of the original plant community, including forbs and legumes, may take many decades. Additions of organic matter and minerals, deferred grazing, prescribed burning, and related management practices described earlier for this ecological site can be beneficial to the rehabilitation.

Community 3.2
Go-back Plant Community

This plant community occurs on areas that were formerly farmed. When tillage operations were discontinued, the areas were allowed to revegetate or “go back” naturally. This was in contrast to artificial reseeding with selected species or a group of species. This is a slow, gradual process that entails many years and many successional changes or stages in the plant community. The speed and extent of revegetation depends on the size of the area, level of grazing management and the proximity of the area to existing seed sources. In the initial stages of revegetation the site is usually dominated by annual forbs such as annual ragweed, Canadian horseweed (Conyza canadensis), common sunflower (Helianthus annuus), Mexican fireweed (Kochia scoparia), annual marshelder, and golden tickseed. Gradually these are replaced by annual grasses including prairie threeawn (Aristida oligantha), prairie cupgrass (Eriochloa contracta), little barley (Hordeum pusillum), cheatgrass (Bromus tectorum), and bearded sprangletop (Leptochloa fusca ssp. fascecularis). Usually plant succession will progress until the plant community is dominated by perennial grasses and grasslike plants including composite dropseed, alkali sacaton, foxtail barley, marsh bristlegrass, silver beardgrass, inland saltgrass, Texas dropseed, buffalograss, Torrey’s rush, and chairmaker’s threesquare. These plants can form a stable community. In time, with prescribed grazing management, other perennial grasses and forbs common in the Reference Plant Community return to the site. Some go-back areas are invaded by trees and shrubs. The more common include Siberian elm, common hackberry, eastern redcedar, eastern cottonwood, black willow, roughleaf dogwood, and Great Plains false willow. Occasional burning is effective in controlling these woody plants.

Resilience management. Following termination of cultivation, total annual production is quite variable and full recovery of the original plant community, including forbs and legumes, may take many decades. Additions of organic matter and minerals, deferred grazing, prescribed burning, and related management practices described earlier for this ecological site can be beneficial to the rehabilitation.

Transition 1 to 2
State 1 to 2

Changes from a Grassland State to a Woody State lead to changes in hydrologic function, forage production, dominant functional and structural groups, and wildlife habitat. Understory plants may be negatively affected by trees and shrubs by a reduction in light, soil moisture, and soil nutrients. Increases in tree and shrub density and size have the effects of reducing understory plant cover and productivity, with desirable forage grasses often being most severely reduced (Eddleman, 1983). As vegetation cover changes from grasses to trees, a greater proportion of precipitation is lost through interception and evaporation; therefore, less precipitation is available for producing herbaceous forage or for deep drainage or runoff (Thurow and Hester, 1997). Tree and shrub establishment becomes increasingly greater while fine fuel loads decrease. As trees and shrubs increase at levels of greater than 20 percent canopy cover, the processes and functions that allow the Woody State to become resilient are active and dominate over the processes and systems inherent of the Grassland State. Using prescribed fire as a standalone management tool is unsuccessful to eradicate the trees and shrubs due to a lack of fine fuel loads.

Constraints to recovery. A closed canopy cover and lack of fine fuel loads could potentially preclude recovery of the former state.

Transition 1 to 3
State 1 to 3

This transition is triggered by a management action as opposed to a natural event. Tillage, or breaking the ground with machinery for crop production, will move the Grassland State to a Tillage State.

Context dependence. The resilience of the Reference State has been compromised by the fracturing and blending of the native virgin sod. The energy, hydrologic, and nutrient cycles are altered and vary from that of the Grassland State.

Restoration pathway 2 to 1
State 2 to 1

Restoration efforts will be costly and labor-intensive, and it can take many years, if not decades, to return to a Grassland State. Once canopy levels reach greater than 20 percent, estimated cost to remove trees is very expensive and includes high energy inputs. The technologies needed in order to go from an invaded Woody State to a Grassland State include but are not limited to: prescribed burning—the use of fire as a tool to achieve a management objective on a predetermined area under conditions where the intensity and extent of the fire are controlled; brush management— manipulating woody plant cover to obtain desired quantities and types of woody cover and/or to reduce competition with herbaceous understory vegetation, in accordance with overall resource management objectives; and prescribed grazing—the controlled harvest of vegetation with grazing or browsing animals managed with the intent to achieve a specified objective. In addition, grazing at an intensity that will maintain enough cover to protect the soil and maintain or improve the quantity and quality of desirable vegetation. When a juniper tree is cut and removed, the soil structure and the associated high infiltration rate may be maintained for over a decade (Hester, 1996). This explains why the area near the dripline usually has substantially greater forage production for many years after the tree has been cut. It also explains why runoff will not necessarily dramatically increase once juniper is removed. Rather, the water continues to infiltrate at high rates into soils previously ameliorated by junipers, thereby increasing deep drainage potential. In rangeland, deep drainage amounts can be 16 percent of the total rainfall amount per year (Thurow and Hester, 1997).