Subirrigated (Sb)
Scenario model
Current ecosystem state
Select a state
Management practices/drivers
Select a transition or restoration pathway
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Transition T1A
Introduction of non-native invasive species such as Kentucky bluegrass, noxious weeds, etc.
More details -
Transition T2A
Prolonged improper grazing
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Transition T2B
Displacement of native species by non-native invasive species (Kentucky bluegrass, noxious weeds, etc.)
More details -
Transition T2C
Conversion to cropland
More details -
Restoration pathway R3A
Proper grazing management, normal or above-normal moisture, revegetation (management intensive and costly)
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Transition T3B
Conversion to cropland
More details -
Transition T4A
Conversion to cropland
More details -
No transition or restoration pathway between the selected states has been described
Target ecosystem state
Select a state
Description
The Historic Reference State (1) contains one community phase characterized by sedges, and reedgrasses. This state is considered extinct and is included here for historical reference purposes. It evolved under the combined influences of climate, grazing, fire, and floodplain hydrology. In general, this state was resilient to grazing and fire, although these factors could influence species composition in localized areas. Hydrology, particularly of groundwater, was an important ecological driver for this site. Depth and duration of the seasonal water table strongly influenced species composition and productivity.
Submodel
Description
The Contemporary Reference State (2) contains two community phases characterized by sedges, reedgrasses, and other mid-statured rhizomatous grasses. It evolved under the combined influences of climate, grazing, fire, and floodplain hydrology, with hydrology having the greatest influence on cover and production. This state differs from the historical reference state in that it is influenced by introduced plant species and has altered fire and grazing regimes. In general, this state is resilient to grazing and fire, although these factors can influence species composition in localized areas.
Submodel
Description
The Altered State (3) consists of one community phase. The dynamics of this state are driven by long term improper grazing management. Species diversity of sedges is greatly reduced, often consisting of only one species. Rushes and unpalatable forbs increase at the expense of rhizomatous grasses and palatable sedges. Proper grazing management can reduce rush cover and increase the cover of rhizomatous grasses, but this recovery may take decades.
Submodel
Description
The Invaded State (4) occurs when invasive plant species invade adjacent native grassland communities and displace the native species. Data suggest that native species diversity declines significantly when invasive species exceed 30 percent of the plant community. The most common concerns are non-native perennial grasses such as Kentucky bluegrass, which is widespread throughout the Northern Great Plains (Toledo et al., 2014). Kentucky bluegrass is very competitive and displaces native species by forming dense root mats, altering nitrogen cycling, and having allelopathic effects on germination (DeKeyser et al., 2013). It may also alter soil surface hydrology and modify soil surface structure (Toledo et al., 2014). Plant communities dominated by Kentucky bluegrass have significantly less cover of native grass and forb species (Toledo et al., 2014; DeKeyser et al., 2009). Invasive grass species can invade relatively undisturbed grasslands, although it is not clear what triggers them to displace native species. In some cases, they have been found to substantially increase under long-term grazing exclusion (DeKeyser et al., 2009, 2013; Grant et al., 2009), but a consistent correlation to grazing management practices cannot be made at this time. Reduced plant species diversity, simplified structural complexity, and altered biologic processes result in a state that is substantially departed from both the Reference State (1) and the Contemporary Reference State (2).
Noxious weeds such as leafy spurge and Canada thistle are not widespread in MLRA 53A, but they can be a concern in localized areas. These species are very aggressive perennials. They typically displace native species and dominate ecological function when they invade a site. In some cases, these species can be suppressed through intensive management (herbicide application, biological control, or intensive grazing management). Control efforts are unlikely to eliminate noxious weeds, but their density can be sufficiently suppressed so that species composition and structural complexity are similar to that of the Contemporary Reference State (2). However, cessation of control methods will most likely result in recolonization of the site by the noxious species.
Submodel
Description
The Cropland State (5) occurs when land is put into cultivation. Deep, fertile soils and favorable moisture conditions make the Subirrigated ecological site prime farmland. Additionally, its proximity to perennial streams make it possible to apply irrigation. Because of this, many acres of the Subirrigated ecological site have been converted to farmland, particularly along the major rivers. It is most commonly planted to non-native perennial species for production of hay. Common species include alfalfa, orchardgrass, creeping foxtail, and grass/alfalfa mixes. Annual crops such as wheat and barley are occasionally planted in rotation with perennial species. In some cases, irrigation is applied in an attempt to increase production. Flood irrigation is most common but center pivot sprinklers are used in some areas. Cropping and irrigation projects have vastly altered vegetation and hydrology on much of the Subirrigated ecological site. Once the site is converted to production agriculture, land values increase significantly and it is unlikely that the site will be converted back to natural vegetation.
Submodel
Mechanism
Introduction of non-native grass species occurred in the early 20th century. The naturalization of these species in relatively undisturbed grasslands, coupled with changes in fire and grazing regimes, transitions the Reference State (1) to the Contemporary Reference State (2).
Mechanism
Improper grazing practices weaken the resilience of the Contemporary Reference State (2) and drive its transition to the Altered State (3). The Contemporary Reference State (2) transitions to the Shortgrass State (3) when species diversity is severely reduced and mid-statured grasses become rare. Grazing resistant species such as Nebraska sedge and Baltic rush (Juncus arcticus ssp. littoralis) dominate the plant community.
Mechanism
The Contemporary Reference State (2) transitions to the Invaded State (4) when aggressive introduced species or noxious weeds displace native species. The most common concerns on this site are introduced forbs such as curly dock and noxious weeds. The precise triggers of this transition are not clear and further investigation is needed. In addition, other rangeland health attributes, such as reproductive capacity of native grasses and soil quality, have been substantially altered.
Mechanism
Tillage or application of herbicide followed by seeding of cultivated crops such as wheat, barley or introduced hay, transitions the Contemporary Reference State (2) to the Cropland State (5).
Mechanism
A reduction in livestock grazing pressure alone may not be sufficient to return the Altered State (3) to the Contemporary Reference State (2). Nebraska sedge in particular can resist displacement by other species (Hansen et al., 1995). Intensive grazing management and revegetation may be necessary, but these are labor intensive and costly. Therefore, returning the Altered State (3) to the Contemporary Reference State (2) can require considerable energy and cost and may not be feasible within a reasonable amount of time.
Relevant conservation practices
| Practice | External resources |
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Critical Area Planting |
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Prescribed Grazing |
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Range Planting |
Mechanism
Tillage or application of herbicide followed by seeding of cultivated crops such as wheat, barley or introduced hay, transitions the Altered State (3) to the Cropland State (5).
Model keys
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