State 1
Reference State

The Reference State represents what is believed to show the natural range of variability that dominated the dynamics of the ecological site prior to European settlement. Historically, this state ranged from a tall, warm-season grass dominated site to one dominated by deciduous shrubs, saplings, and trees depending upon disturbance regime. The primary disturbance mechanisms for this site in the reference condition included periodic fire and grazing by large herding ungulates. Timing of fires and grazing coupled with weather events dictated the dynamics that occurred within the natural range of variability. Dominance during the herbaceous phases of this state shifted between warm-season and cool-season grasses. Although slight shifts may have occurred in timing of energy capture, hydrologic function, and nutrient cycling between plant community phases within the Reference State (1.0), overall the ecological processes were functioning at near optimum levels. High basal density and deep root systems resulted in low runoff rates and high infiltration rates.

Areas of trees and shrubs existed within this state due to irregularity of burn patterns. Areas which escaped fire may have permitted trees and shrubs to become established. These areas may have served as a seed source for further expansion of the woody dominated plant communities as the fire frequency was altered after settlement.

Community 1.1
Big Bluestem-Switchgrass-Needlegrass/Scattered Shrubs/Scattered Trees

Interpretations are based primarily on the Big Bluestem-Switchgrass-Needlegrass/Scattered Shrubs/Scattered Trees Plant Community. This is also considered to be the Reference Plant Community (1.1). This community evolved with grazing by large herbivores and occasional prairie fire. The vegetation was about 70 percent grasses and grass-like plants, 10 percent forbs, 10 percent shrubs, and 10 percent trees. Major grasses included big bluestem, switchgrass, green needlegrass, Indiangrass, and western wheatgrass. Other grasses that occurred within this community included slender wheatgrass, thickspike wheatgrass, Canada wildrye, little bluestem, sideoats grama, and blue grama. Major forbs and shrubs included American licorice, sunflower, goldenrod, and western snowberry. Green ash, American elm, bur oak, and other native tree species occurred as scattered individuals to larger patches.

This plant community was well adapted to the Northern Great Plains climatic conditions. Individual species varied greatly in production depending on growing conditions (timing and amount of precipitation and temperature). Community dynamics, nutrient cycle, water cycle, and energy flow were properly functioning. Due to the diversity of warm- and cool-season species within this plant community phase, energy capture was spread more evenly throughout the growing season compared to other plant community phases within this state. Plant litter was properly distributed in contact with the soil surface and with very little movement offsite. Natural plant mortality was very low. The diversity in plant species allowed for high drought tolerance. Runoff from adjacent sites and moderate or high available water capacity provided a favorable soil-water-plant relationship.

State 2
Native/Invaded State

The Native/Invaded State (2.0) represents the more common range of variability that exists with higher levels of grazing management but in the absence of periodic fire due to fire suppression. The invasion of non-native cool-season grasses has also altered the natural range of variability for this ecological site. Currently this state is dominated by tall native warm-season grasses, but invasive introduced cool-season grasses are now present in all community phases of this state. It can be found on areas that are properly managed with grazing and/or prescribed burning, and sometimes on areas receiving occasional short periods of rest. Many times, this state appears as a mosaic of community phases caused primarily by continuous season-long grazing. Native cool- and warm-season species can decline and a corresponding increase in non-native cool-season grasses will occur. Non-native cool-season grasses will typically make up less than 15 percent of total annual production. Preliminary studies tend to indicate that when Kentucky bluegrass exceeds 30 percent of the plant community and native grasses represent less than 40 percent of the plant community composition a threshold has been crossed to an Invaded State (5.0). These invaded plant communities that are dominated by Kentucky bluegrass will have significantly less cover and diversity of native grasses and forb species (Toledo, D. et al., 2014).

Community 2.1
Big Bluestem-Switchgrass-Needlegrass-Non-Native Cool-Season Grasses (<15%)/Scattered Shrubs/Scattered Trees

This plant community phase is similar to the Big Bluestem-Switchgrass-Needlegrass/Scattered Shrub /Scattered Trees Plant Community (1.1) but it also contains minor amounts of non-native invasive grass species such as Kentucky bluegrass. smooth brome, and possibly timothy (up to about 15 percent by air-dry weight). The potential vegetation is about 70 percent grasses or grass-like plants, 10 percent forbs, 10 percent shrubs, and 10 percent mature trees. The community is dominated by warm-season grasses. Major grasses include big bluestem, switchgrass, green needlegrass, Indiangrass, and western wheatgrass. Other grasses that occur within this community include slender wheatgrass, thickspike wheatgrass, Canada wildrye, little bluestem, sideoats grama, and blue grama. Major forbs and shrubs include American licorice, sunflower, goldenrod, chokecherry, and western snowberry. Green ash, American elm, bur oak, and other native tree species occur as scattered individuals to larger patches.

Ecological processes are functioning at levels near what would be expected for the Reference State (1.0) although nutrient cycling may be somewhat altered due to changes in disturbance regimes (lack of fire, frequency and intensity of grazing events) and energy capture may be shifted slightly to more late spring, early summer.

This plant community is resilient and well adapted to the Northern Great Plains climatic conditions. The diversity in plant species allows for high drought tolerance. This is a sustainable plant community in regard to soil and site stability, watershed function, and biologic integrity.

Community 2.2
Rhizomatous Wheatgrass-Kentucky Bluegrass (<15%)-Big Bluestem/Scattered Shrubs/Scattered Trees

This plant community is characterized by a shift to mid-cool-season rhizomatous grasses with minor amounts of tall warm-season and mid-cool-season bunchgrasses. The vegetation is about 70 percent grasses and grass-like plants, 10 percent forbs, 10 percent shrubs, and 10 percent trees. Dominant grasses would include western wheatgrass and Kentucky bluegrass with minor amounts of needlegrasses, big bluestem, and switchgrass. Major forbs would include Cumin ragweed (western ragweed), goldenrods, and western yarrow. Chokecherry and snowberry would be the dominate shrubs. Green ash, plains cottonwood, and possibly bur oak will be present in most areas. Energy capture by this plant community phase has shifted from late spring and summer to early spring through early summer.

Pathway 2.1A
Community 2.1 to 2.2

Continuous seasonal grazing which includes grazing at moderate to heavy stocking levels at the same time of year each year; or continuous season-long grazing; will shift this community (2.1) to the Rhizomatous Wheatgrass-Kentucky Bluegrass (<15%)/Shrubs/Scattered Trees Plant Community (2.2).

Pathway 2.2A
Community 2.2 to 2.1

Prescribed grazing (proper stocking levels, alternating season of use, and providing adequate recovery periods); possibly prescribed burning in combination with prescribed grazing; will convert this plant community (2.2) to the Big Bluestem-Switchgrass-Needlegrass-Rhizomatous-Non-Native Cool-Season Grass (<15%)/Shrubs/Scattered Trees Plant Community (2.1).

State 3
Invaded State

This Invaded State (3.0) is the result of invasion and dominance of introduced species. The Invaded State is characterized by the dominance of Kentucky bluegrass and smooth brome, and an increasing thatch layer that effectively blocks introduction of other plants into the system. Plant litter accumulation tends to favor the more shade-tolerant, introduced grass species. The nutrient cycle is also impaired, and the result is typically a higher level of nitrogen, which also favors the introduced species. Increasing plant litter decreases the amount of sunlight reaching plant crowns, thereby shifting competitive advantage to shade-tolerant introduced grass species. Studies indicate that soil biological activity is altered, and this shift apparently exploits the soil microclimate and encourages growth of the introduced grass species. Once the threshold is crossed, a change in grazing management alone cannot cause a reduction in the invasive grass dominance. Preliminary studies would tend to indicate this threshold may exist when Kentucky bluegrass exceeds 30 percent and native grasses represent less than 40 percent of the plant community composition. Plant communities dominated by Kentucky bluegrass have significantly less cover and diversity of native grasses and forb species (Toledo, D., et al., 2014).

Once this state is well established, even drastic events such as high intensity fires driven by high fuel loads of litter and thatch may not result in more than a very short-term reduction of Kentucky bluegrass. These events can reduce the dominance of Kentucky bluegrass, but due to the large amount of rhizomes in the soil, there is little opportunity for the native species to establish and dominate before Kentucky bluegrass rebounds and again dominates the system.

Community 3.1
Kentucky Bluegrass (>30%)-Smooth Brome/Scattered Shrubs/Scattered Trees

This plant community phase is a result of heavy, continuous grazing, excessive haying, or extended periods of non-use and no fire. It is characterized by a dominance of Kentucky bluegrass and smooth brome. The dominance is at times so complete that other species are difficult to find on the site. A thick duff layer also accumulates at or above the soil surface through non-use. Vegetative production can be variable in this plant community. The period that forage palatability is high is relatively short, as these cool-season species mature rapidly.

Grasses constitute about 70 percent of the production with forbs contributing 10 percent, shrubs 10 percent, and trees 10 percent. Dominant forbs include white sagebrush (cudweed sagewort), goldenrod, and American licorice. Shrubs would include snowberry, plum, chokecherry, and prairie rose.

Grazing pressure alone cannot induce a reduction in sodgrass dominance. Production is limited to the sod forming species. Infiltration continues to decrease, and runoff increases. Energy capture into the system is restricted to early season low producing species. The opportunity for high intensity spring burns is reduced by early green-up and increased moisture and humidity at the soil surface. Nutrient cycling is greatly reduced, and native plants have great difficulty becoming established.

Community 3.2
Kentucky Bluegrass Sod/Remnant Shrubs/Trees/Weedy Annuals and Perennial Forbs

This plant community is characterized by a dense Kentucky bluegrass sod. Kentucky bluegrass is the dominant grass species with minor amounts of other grasses such as western wheatgrass and needlegrass, as well as, grass-likes still represented. Forb species would include curly-cup gumweed, western yarrow, and stiff goldenrod. Shrubs are very limited but may include snowberry.

This plant community is resistant to change, and if disturbed, it is resilient. Bluegrass will increase under grazing pressure. Cool, moist climatic conditions will also tend to increase bluegrass production. The opportunity for spring burns can be limited due to lack of fine fuel and early green up. Production is reduced due to lack of plant vigor. Infiltration is greatly reduced due to the dense sod while energy capture is shifted to early spring through early summer.

Pathway 3.1A
Community 3.1 to 3.2

Heavy, continuous seasonal grazing (stocking levels well above carrying capacity for extended portions of the growing season, and at the same time of year each year) or heavy, continuous season-long grazing will convert this plant community (3.1) to the Kentucky Bluegrass Sod/Remnant Shrubs/Trees/Weedy Annual and Perennial Forbs Plant Community (3.2).

Pathway 3.2A
Community 3.2 to 3.1

Prescribed burning followed by prescribed grazing (alternating season of use and providing adequate recovery periods) or periodic light to moderate grazing, possibly including periodic rest, may convert this plant community (3.2) to the Kentucky Bluegrass-Smooth Brome/Scattered Shrubs/Trees Plant Community (3.1).

State 4
Wooded Overstory State

Historically, this state existed as small patches of trees and shrubs scattered across the site. Repeated intense disturbances (e.g., fire coupled with grazing) would have reverted these smaller patches of trees to the herbaceous dominated Reference State (1.0). In pre-European times, periodic low intensity fires typically would have maintained these small, wooded patches in a tree dominated state. Alterations to the historic fire and grazing disturbance regimes have resulted in these scattered tree/shrub patches forming almost continuous woody dominated plant communities across the site. This state is characterized by an overstory of tall trees, an understory of shrubs, and depending upon the amount of canopy cover, an herbaceous understory of grasses, sedges, and forbs.

The dynamics of the Wooded Overstory State (4.0) are largely due to flooding and the natural successional changes, starting with cottonwood and shrub establishment, and eventually the development of a green ash and boxelder plant community. The successional process can restart following another flooding event. Water control structures which limit flooding, livestock grazing, heavy wildlife browse, fire, the introduction of non-native, cool-season grasses, and encroachment of juniper can alter the dynamics of this site, resulting in old remnant stands of trees with little, if any regeneration.

Community 4.1
Cottonwood/Prunus-Snowberry/Forbs/Grasses

This plant community typically develops after a flooding event. Flooding reduces herbaceous competition through scouring and silt deposition at the soil surface, which provides a site for regeneration and establishment of cottonwood and shrubs.

Long-term rest periods during the growing season will be required to allow cottonwood seedlings to reach a height which is out of reach of livestock. Late winter and early spring grazing will also need to be closely monitored to prevent grazing of cottonwood seedlings during early spring leaf development. Restricted grazing during late-summer and fall grazing when browsing is common is also necessary for this plant community to establish. Plains cottonwood develop quickly into a robust tree so grazing deferment may only be required for 3 to 4 years.

Trees will range from seedlings to saplings, and the herbaceous understory will still be productive as a result of the filtered canopy of the deciduous trees. Understory shrubs, primarily plum, chokecherry, and snowberry will likely establish. However, other species, including silver buffaloberry, silver sagebrush, big sagebrush, and currants can occur and make up a significance percentage of the shrub layer.

Community 4.2
Mature Cottonwood-Green Ash-Boxelder/Prunus-Snowberry/Forbs/Grass Understory

This plant community develops over time with prescribed grazing and no flooding or fire. Mature cottonwood trees and woody shrubs provide a suitable microclimate for establishment of other deciduous trees. Green ash and boxelder are typically the first trees to establish, but other species such as hackberry and possibly bur oak will establish as well. Regeneration of woody species will normally be evident (i.e., seedlings and saplings should be present). The herbaceous plant community will remain relatively productive but will be reduced somewhat from the Reference Plant Community (1.1). This is due mainly to the competition from the woody shrub understory.

Community 4.3
Green Ash-Boxelder/Prunus-Snowberry/Forbs/Grass Understory

This plant community develops over time, with prescribed grazing and no flooding. Mature cottonwood trees will likely remain in lesser numbers, but the dominant trees will normally consist of green ash and boxelder. At times there will be a mix of all three species; however, some areas will be dominated by one or two of these species. Woody shrubs will remain in the understory, but typically in lesser amounts than in the previous two plant communities. While somewhat reduced, the herbaceous understory will remain relatively productive. The trees will mostly be in the mature stage, but regeneration will normally be evident (i.e., seedlings and saplings should be present).

Pathway 4.1A
Community 4.1 to 4.2

No flooding and long-term prescribed grazing that manages the herbaceous understory, but is not detrimental to woody regeneration, will allow this plant community (4.1) to develop into the Mature Cottonwood-Immature Green Ash-Boxelder/Prunus-Snowberry/Forbs/Grass Understory Plant Community (4.2). Existing saplings must be large enough to avoid damage by livestock and wildlife for this pathway to occur.

Pathway 4.2A
Community 4.2 to 4.1

Flooding, and possibly fire, which opens-up the herbaceous understory and allows for woody regeneration, followed by long-term prescribed grazing that manages for woody regeneration and establishment will shift this plant community (4.2) back to the Cottonwood/Prunus-Snowberry/Forbs/Grasses Plant Community (4.1).

Pathway 4.2B
Community 4.2 to 4.3

No flooding, no fire, and long-term prescribed grazing that manages the herbaceous understory but is not detrimental to woody regeneration, and time will transition this plant community (4.2) to the Green Ash-Boxelder/Prunus-Snowberry/Forbs/Grass Understory Plant Community (4.3).

Pathway 4.3A
Community 4.3 to 4.1

Flooding, and possibly fire, which opens up the herbaceous understory and allows for woody regeneration, followed by long-term prescribed grazing that manages for woody regeneration and establishment will shift this plant community (4.3) back to the Cottonwood/Prunus-Snowberry/Forbs/Grasses Plant Community (4.1).

State 5
Wooded Invaded State

The Woody Invaded State develops as a result of continuous season-long grazing, or continuous seasonal grazing and no fire combined with the invasion and establishment of Russian olive, saltcedar, or conifer trees. With time, the cottonwood, boxelder, and ash trees that survive become mature, with little or no regeneration. This is due mainly to grazing of seedlings and saplings. Wildlife browse can also contribute to the loss of native tree and shrub regeneration. Grazing that limits regeneration also results in a reduction of the desirable native herbaceous species, often resulting in a dominance of species such as bluegrass and smooth brome, and forbs such as western ragweed, Canada thistle, burdock, and hound’s tongue.

Community 5.1
Scattered Mature Native Trees-Russian Olive/Ponderosa Pine/Shrubs/Forbs/Non-Native Cool-Season Grasses

This plant community developed due to the lack of natural occurring flooding events, native woody regeneration, and continuous season-long grazing without adequate recovery periods. Older mature trees remain, including cottonwood, boxelder, and green ash. The trees are scattered, and the site may have a “park-like” appearance with few trees and reduced understory. If grazed during the winter, the increased durations of livestock loitering can result in manure accumulations and soil compaction which will reduce the vigor of the native understory plant community. Kentucky bluegrass and smooth brome continue to persist as dominant grass species at reduced production rates. The presence of non-desirable forb species such as Canada thistle, burdock, and hound’s tongue can be prolific and difficult to control. When invaded by Russian olive and/or saltcedar these species will increase dramatically over time and will eventually dominate the site.

Transition T1A
State 1 to 2

Continuous season-long grazing; excessive haying; long-term light grazing; or no use and no fire; and the invasion of non-native cool-season grasses will transition the Reference State (1.0) to the Native/Invaded State (2.0).

Transition T1B
State 1 to 4

Flooding, which opens the herbaceous understory and allows for woody establishment; no fire; long-term prescribed grazing to promote tree survival; and an extended period of time will transition the Reference State (1.0) to the Wooded Overstory State (4.0).

Transition T2A
State 2 to 3

Continuous heavy grazing; excessive haying; or long-term light grazing will result in an increase in non-native cool-season grasses and cause a transition from the Native/Invaded State (2.0) to the Invaded State (3.0). Extended periods of non-use and no fire, and heavy litter build-up will favor non-natives cool-season grasses transition this state to the Invaded State (3.0).

Transition T2B
State 2 to 4

Flooding, which opens the herbaceous understory and allows for woody establishment; no fire; long-term prescribed grazing to promote tree survival; and an extended period of time will transition the Native/Invaded State (2.0) to the Wooded Overstory State (4.0).

Restoration pathway R3A
State 3 to 2

Long-term prescribed grazing (moderate stocking levels coupled with adequate recovery periods, or other grazing systems intended to treat specific species dominance, or periodic light to moderate stocking levels, possibly including periodic rest) may lead the Invaded State (3.0) over a threshold to the Native/Invaded State (2.0). Prescribed burning may also be needed to suppress cool-season invasive grasses. This will likely take a long period of time, possibly up to ten years or more, and recovery may not be attainable. Success depends upon whether native reproductive propagules remain intact on the site.

Transition T3A
State 3 to 5

Encroachment of juniper trees from upland sites, or invasion of non-native deciduous trees; no fire for extended periods of time; continuous season-long grazing, or continuous seasonal grazing, and time; will cause a transition from the Invaded State (3.0) to the Wooded Invaded State (5.0). Canopy cover increases as trees increase in size, which alters microclimate and reduces fine fuel amounts, resulting in reduced fire intensity and frequency.

Context dependence.Encroachment of juniper trees from upland sites, or invasion of non-native deciduous trees; no fire for extended periods of time; continuous season-long grazing, or continuous seasonal grazing.

Transition T4A
State 4 to 2

Fire; invasion of non-native, cool-season grasses; excessive haying; continuous season-long grazing or continuous seasonal grazing resulting in little woody regeneration; and time; will transition the Wooded Overstory State (4.0) to the Native/Invaded State (2.0).

Transition T4B
State 4 to 5

Encroachment of juniper from upland sites, and/or invasion of non-native deciduous trees, coupled with no fire and continuous season-long grazing or continuous seasonal grazing will transition the Wooded Overstory State (4.0) to the Wooded Invaded State (5.0).

Transition T5A
State 5 to 3

Fire, brush management to remove Russian olive; continuous season-long grazing; or continuous seasonal grazing will transition the Wooded Invaded State (5.0) to the Invaded State (3.0).