Sandy Lowland

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 and mid, warm and cool season grasses, forbs, and shrubs. Plant community 2 is dominated by sand dropseed and western wheatgrass and combined with a minor component of reference community plant species. The third plant community that makes up the grassland state is called an at-risk plant community. This plant community is most vulnerable to exceeding the resilience limits of the grassland state and transitioning to an alternative state. This plant community is dominated by sand sagebrush and blue grama.

Continuous use, an absent forage and animal balance, in combination with inadequate rest of the dominant Reference Plant Community species, will reduce the production of the bluestems allowing western wheatgrass and sand dropseed to increase. To a small extent, some buffalograss will also increase. After the vegetation is reduced to western wheatgrass and heavy continuous grazing of the dominant plant species continues, kochia, Russian thistle, and other undesirable annuals can invade the area.

Once most of the taller species are eliminated from the site through grazing pressure and/or dry weather, regaining the potential vegetation through management is extremely slow and may take several decades. Where remnants of the taller species remain, grazing management that includes a forage and animal balance and scheduled rest during the growing season can be effective in returning the site to near its potential.

Cottonwood trees and sandbar willow trees can persist on this site due to fire suppression. These trees establish well and are a minor component of the reference vegetation of this 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 Woody State is supported by empirical data and is defined by one plant community phase.
The Grassland State ecosystem has been driven beyond the limits of ecological resilience, and has crossed a threshold into the Woody State. The designation of the Woody State denotes changes in plant species composition. This change in plant species affects the hydrology, erosion potential, forage production, and wildlife habitat of the site. Understory plants may be negatively affected by shrubs, reducing the availability of light, soil moisture, and soil nutrients. As the size and density of shrubs increase, the cover and productivity of understory plants decrease. Desirable forage grasses often are the most severely reduced (Eddleman, 1983). As the vegetative cover changes from grasses to shrubs, a greater proportion of precipitation leaves rangeland via evaporation; therefore, less precipitation is available for producing herbaceous forage or for deep drainage or runoff (Thurow and Hester, 1997).

As establishment of shrubs increases, fine-fuel loads decrease. When the shrubs increase to greater than 30 percent canopy, the processes and functions that allow this state to become resilient become active and dominate over a grassland state. Prescribed fire can become an ineffective tool to eradicate the shrubs due to the lack of fine-fuel loads.

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

Description

The reference 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 soil properties and plant communities. These changes affect the hydrologic function, biotic integrity, and soil and site stability of the ecological site.

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 on a continual basis.

Submodel