Recharge Closed Depression (CdR)

Description

The Historic Reference state (1) contained three community phases characterized by varying degrees of seasonal ponding. This state is considered extinct and is included here for historical reference purposes. Seasonal ponding was a key dynamic on this site and varied depending on annual precipitation patterns and catchment size. Vegetation was characterized concentric rings, or zones, within the depression that correspond to the hydroperiod of that particular zone. Some phases only exhibited one vegetation zone dominated by facultative upland species while other phases exhibited two or more zones with the most hydrophytic vegetation in the center of the depression and subsequent, drier plant communities toward the edges.

Submodel

Description

The Current Potential state (2) contains three community phases. Seasonal ponding is a key dynamic on this site and varies depending on annual precipitation patterns and catchment size. This state differs from the historical reference state in that it is influenced by nonnative plant species and has altered fire and grazing regimes. Vegetation is characterized concentric rings, or zones, within the depression that correspond to the hydroperiod of that particular zone. The Ephemeral Phase (2.1) may only exhibit one vegetation zone dominated by facultative upland species. Other phases may exhibit two or more zones with the most hydrophytic vegetation in the center of the depression and subsequent, drier plant communities toward the edges.

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Description

The Invaded state (3) 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 Kentucky bluegrass and reed canarygrass. Kentucky bluegrass is widespread throughout the Northern Great Plains (Toledo et al., 2014) and mainly affects the ephemeral and temporarily ponded phases of this site. It 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). Reed canarygrass is a vigorous, productive, long-lived, perennial, sod-forming grass that mainly affects the temporarily ponded or seasonally ponded phases of this ecological site. Although native to North America, it may become weedy or invasive in some habitats and may displace desirable vegetation if not properly managed (USDA-NRCS, 2002). Invasive grass species can invade relatively undisturbed sites, and 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.

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 Current Potential state (2). However, cessation of control methods will most likely result in recolonization of the site by the noxious species.

Submodel

Description

The Undrained Cropland state (4) occurs when native vegetation is killed out, either by tillage or by herbicide application, and the site is seeded to annual crops. No other alterations are made to the natural hydrology or soils. This state typically only occurs in the Ephemeral Phase (2.1) and the Temporarily Ponded Phase (2.2). In this state the site is suitable for spring seeded crops such as spring wheat and barley, although seeding of crops may be delayed 2 to 3 weeks due to wet soil conditions. In wet years, this state may be too wet to farm and will transition to the Wet/Foxtail Barley Phase (4.2).

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Description

The Impounded state (5) occurs when water is artificially impounded on the site by damming or excavation. Water may be impounded for livestock water or for wildlife. Impoundment of water typically transitions the site to a semi-permanent wetland with open water, deep marsh, and drawdown vegetation zones. In many cases impoundment creates a larger wetland with high quality habitat for wildlife. In other cases, such as when an excavated pond is constructed in the center of the depression, a small semi-permanent wetland is created in the center while the remainder of the depression is drained, thus reducing total wetland area. In either case the natural hydrology of the site is significantly altered, resulting in a new state with different plant communities and ecological dynamics.

Submodel

Description

The Drained Cropland State (6) occurs when the site is drained, tilled or sprayed, and seeded to annual crops. Surface water is typically drained by means of surface ditches, diversions, or both. Following drainage, remaining native vegetation is killed out either by tillage or herbicide application, then the site is seeded to annual crops. The hydrology of the site is significantly altered and no longer functions in its natural condition.

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