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Peabody Twentymile Coal Company <br />2004 Fish Creek AVF Riparian Vegetation Monitoring <br />1. Little or no effect; <br />2. An increase in hydric vegetation dominated communities associated with <br />surface subsidence and closer proximity of the rooting zone to <br />groundwater, as well as an increase in impounded surface water <br />resources; or <br />3. Diminution or cessation of surface water flows leading to a reduction in <br />hydric vegetation communities. <br />Observations in 2003 of drowned sage communities in swamped depressions <br />and bank-full sections of the creek suggested that hydric vegetation increased <br />with increased surface subsidence. In 2004, some form of subsidence was <br />observed on 5 of the 12 transects. Some of the 2004 observations supported the <br />conclusions of the 2003 study; sage brush communities were being drowned and <br />replaced by hydric vegetation in selected areas within the Fish Creek flood plain. <br />A less dramatic effect of subsidence may be a shallower depth to the <br />groundwater table. The light changes in the groundwater elevation may be <br />resulting in a progressive change in vegetation composition. This change in <br />vegetation composition between 2003 and 2004 was recorded at Transect 12, <br />where Silver sagebrush and native mesic graminoids are in the process of <br />colonizing a former mesic improved pasture. Alternatively, this shift in <br />vegetation community composition may be caused by climate and/or grazing <br />pressure. Thus, two trends were observed at Fish Creek: first, sage communities <br />were being replaced by hydric species in swamped depressions associated with <br />lower elevations, and second, historic improved pastureland communities were <br />being invaded by Silver sagebrush and native mesic graminoids. Future <br />monitoring efforts will be required to substantiate any projection regarding the <br />effects of subsidence on the vegetation community composition and riparian <br />characteristics of Fish Creek. <br />Habitat Management, Inc. Page 4 10/S/2004 <br />