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The degree of grazing has a significant impact on the ecological dynamics of the site.This region was historically <br /> occupied by large grazing animals such as bison and elk, along with pronghorn and mule deer. Grazing by these <br /> large herbivores,along with climatic fluctuations, and seasonal weather fluctuations, had a major influence on the <br /> dynamics of the ecology of this site. Deer and pronghorn are widely distributed throughout the MLRA. Secondary <br /> influences of herbivory by species such as prairie dogs and other small rodents, insects and root feeding organisms <br /> have impacted the vegetation and continues today. <br /> Historically, it is believed, grazing patterns by herds of large ungulates was driven by water distribution, precipitation <br /> events, drought events, and fire. It is believed that grazing periods would have been shorter,followed by longer <br /> recovery periods.These large migrating herds impacted the ecological processes of nutrient and hydrologic cycles, <br /> by urination,trampling (incorporation of litter into the soil surface), and breaking of surface crust, to increase water <br /> infiltration. <br /> This is an important site for livestock grazing, especially beef cattle.Today the management of livestock grazing by <br /> humans has been a major influence on the ecological dynamics of the site.This management, coupled with the <br /> effects of annual climatic variations, largely dictates the plant communities for the site. Prescribed grazing that <br /> mimics the historic grazing of herds of migratory herbivores, as described earlier, has been shown to result in <br /> desired improvements based on management goals for this ecological site. <br /> Recurrent drought has historically impacted the vegetation of this region. Changes in species composition will vary <br /> depending upon the duration and severity of the drought cycle, and prior grazing management. Recent drought <br /> events(since 2002) have increased mortality of blue grama and other bunchgrasses significantly in some locales. <br /> This site developed with occasional fires being part of the ecological processes. Historic fire frequency(pre- <br /> industrial), is estimated at 10-14 years (Guyette 2012), randomly distributed, and started by lightning at various <br /> times throughout the growing season. Early human inhabitants were also likely to start fires for various reasons <br /> (deliberate or accidental). It is believed that fires were set as a management tool for attracting herds of large <br /> migratory herbivores(Stewart, 2002). The impact of fire over the past 100 years has be relatively insignificant due to <br /> the human control of wildfires and the lack of acceptance of prescribed fire as a management tool. <br /> Grazing by large herbivores,without adequate recovery periods following each grazing occurrence,will cause blue <br /> grama to increase. Blue grama may eventually form a sod-like appearance. Prairie sandreed, sand bluestem, and <br /> switchgrass will decrease. Prairie sandreed may persist in remnant amounts protected by remaining shrubs. Cool <br /> season grasses such as needleandthread and western wheatgrass will decrease in frequency and production. Key <br /> shrubs such as western sand cherry and fourwing saltbush will decrease in frequency and production. American <br /> vetch and other highly palatable forbs will also decrease. Fendler threeawn, annuals and bare ground increases <br /> under heavy continuous grazing, excessive defoliation, or long-term non-use. Much of this ecological site has been <br /> tilled and used for crop production. Other areas of this ecological site have been converted to suburban residence <br /> and small acreages, especially near the larger communities. <br /> The following is a diagram illustrates the common plant communities that can occur on the Sandy Plains site and the <br /> community pathways(CP)among plant communities. Plant Communities are identified by 1.1, 1.2 etc. and are <br /> described in the narrative. Bold lines surrounding each state represent ecological thresholds. Transitions(T) <br /> indicate the transition across an ecological threshold to another state. Once a threshold has been crossed into <br /> another state, it may not be feasible to return to the original state, even with significant management inputs and <br /> practices.The ecological processes plant communities,community pathways, transition and/or restoration <br /> pathways will be discussed in more detail in the plant community descriptions following the diagram. <br /> State and transition model <br />