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management of livestock grazing has been a major influence on the ecological <br /> dynamics of the site. This management, coupled with the effects of annual <br /> climatic variations, largely dictates the plant communities for the site. <br /> Recurrent drought has historically impacted the vegetation of this region. <br /> Changes in species composition will vary depending upon the duration and <br /> severity of the drought cycle, and prior grazing management. Recent drought <br /> events (since 2002), have significantly increased mortality of blue grama and <br /> buffalograss in some locales. <br /> This site developed with occasional fire as part of the ecological processes. <br /> Historic fire frequency (pre-industrial), is estimated at 10-14 years (Guyette, <br /> 2012), randomly distributed, and started by lightning at various times <br /> throughout the growing season. It's thought that early human inhabitants also <br /> were likely to start fires for various reasons (deliberate or accidental). It is <br /> 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 <br /> years has been relatively insignificant due to the human control of wildfires <br /> and the lack of acceptance of prescribed fire as a management tool. <br /> Grazing by large herbivores, without adequate recovery periods following each <br /> grazing occurrence, will cause blue grama and buffalograss to increase. Blue <br /> grama and/or buffalograss may eventually form a sod-like appearance. Cool- <br /> season grasses such as western wheatgrass and green needlegrass will <br /> decrease in frequency and production. Eventually green needlegrass will be <br /> removed and western wheatgrass may persist in depressions. Fourwing <br /> saltbush will decrease in frequency and production. American vetch and other <br /> highly palatable forbs also will decrease. Fendler threeawn, ring muhly, <br /> annuals, and bare ground increases under heavy continuous grazing, <br /> excessive defoliation, or long-term non-use. Much of this ecological site has <br /> been tilled and used for crop production. Other areas of this ecological site <br /> have been converted to suburban residences and small acreages, especially <br /> near the larger communities. <br /> Mechanical treatment consisting of contour pitting/furrowing, terracing, <br /> chiseling, and disking was practiced in the past. It was theorized that the use <br /> of this high-input technology would improve production and plant composition <br /> on rangeland. These high-cost practices have shown to have no significant <br /> long- term benefits on production or plant composition, and have only resulted <br /> in a permanently rough ground surface. Prescribed grazing that mimics the <br /> historic grazing of herds of migratory herbivores, as described earlier, has <br /> been shown to result in desired improvements based on management goals <br /> for this ecological site. <br /> The following is a diagram illustrates the common plant communities that can <br /> occur on the Sandy Plains site and the community pathways (CP) among <br /> 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 <br /> ecological thresholds. Transitions (T) indicate the transition across an <br /> 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 <br /> significant management inputs and practices. The ecological processes plant <br />