Sandy Plains

Description

The grassland state is supported by empirical data and is defined by three native plant communities that are a result of periodic fire, drought, and herbivore and ungulate grazers. These events are part of the natural disturbance regime and climatic process that contribute to the development of the site. The Reference Plant Community consists of tall, mid, short, warm and cool season grasses, forbs, and shrubs. Plant Community 1.2 is dominated by sand dropseed and blue grama in combination with a minor component (2-10 percent composition by weight) of reference community plant species. This plant community is vulnerable to exceeding the resilience limits of the Grassland State and transitioning to state 2. Plant Community 1.3 is vulnerable to exceeding the resilience limits of the Grassland State as well. This plant community is dominated (40-100 percent composition by weight) by Fendler threeawn and sand dropseed, while subdominant (10-40 percent composition by weight) species include annuals. More field investigations and evaluations are necessary to assess Plant Community 1.3 in regard to resilience and changes in vegetation, soil, and hydrology of the site.

The following paragraphs are narratives for each of the described plant communities. These plant communities may not represent every possibility, but they probably are the most prevalent and repeatable plant communities that exist on this ecological site. The plant composition table shown below has been developed from the best available knowledge at the time of this revision. As more data is collected, some of these plant communities may be adjusted or removed and new ones may be added. None of these plant communities should necessarily be thought of as “Desired Plant Communities." According to the USDA NRCS National Range and Pasture Handbook, Desired Plant Communities will be determined by the decision-makers and will meet minimum quality criteria established by NRCS. The main purpose for including any description of a plant community here is to capture the current knowledge and experience at the time of this revision.

Submodel

Description

The reference grassland state ecosystem has been driven beyond the limits of ecological resilience and has crossed a threshold into the sod-bound state. The designation of the sod-bound state denotes changes in infiltration, runoff, bulk density and species composition. The ecosystem is affected by changes in soil properties, water movement and the plant community. These changes, in turn, affect the hydrologic functionality, biotic integrity, and soil and site stability of the ecological site.

With long term, heavy, continuous grazing, blue grama will become the dominant species and have a sod bound appearance. Unable to withstand the grazing pressure, only a remnant population of western wheatgrass remains.

Species diversity has been reduced further. Water infiltration is reduced due to the sod nature of the blue grama. Runoff is increased.

Vegetation type affects the amount and structure associated cover, therefore the infiltration rate differs among vegetation types. The amount of cover, and hence the rate of infiltration, is usually greatest under trees and shrubs, followed in decreasing order by bunchgrass, shortgrass, and bare ground (Blackburn 1975; Thurow et al. 1986).

Specific dynamic soil property changes between the grassland state and the sod-bound state has been documented. As plant community cover decreases from bunchgrasses to more of the sod grasses there is a decrease in infiltration and interception and an increase in surface runoff.

There is no known timeframe or restoration pathway success from this state to the grassland state. Experience suggests that long-term prescription grazing to include a forage and animal balance, adequate recovery periods following each grazing event over long periods of time will gradually move this plant community toward the grassland state. This process is not well documented and may take greater than 40 years.

This alternative state will be tested through long-term observation of ecosystem behavior and repeated application of conservation and restoration practices. This state should be re-evaluated and refined continually.

Submodel

Description

The Grassland State ecosystem has been driven beyond the limits of ecological resilience and has crossed a threshold into the Tillage
State. The designation of the Tillage State denotes changes in infiltration, runoff, bulk density, aggregate stability, and species composition. The changes in inherent soil properties, water movement, and the plant community, affect changes in the ecosystem affecting the hydrologic functionality, biotic integrity, and soil and site stability.

This group includes two separate vegetation states that are highly variable. They are derived through two distinct management scenarios, and are not related successionally. Infiltration, runoff and soil erosion varies depending on the vegetation present.

The tillage state consist of abandoned cropland that has been naturally revegetated (go-back) or planted/seeded to grassland. 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. Go-back communities are difficult to define due to the variability of plant communities that exist. Many of these communities are represented by the genus Aristida (three-awns).

This is an alternative state because the ecological functions i.e. dynamic soil properties and plant communities are not fully restored to that of the reference state. 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)

This alternative state should be tested through long-term observation of ecosystem behavior and repeated application of conservation and restoration practices. This state should be re-evaluated and refined continually.

Submodel