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•~ • Vigor assessments form this year were compared with data from last year. This comparison suggests a significant and dramatic decline in tree vigor (including some mortality) at Transect 2 (See figure 2). Figure 2 indicates that a drop in the water table of 2.0 feet or more is associated with significant declines in vigor in mature stands of cottonwoods. For instance, note tFie trees in cells 2N and 2S showed little decline in vigor. Correspondingly, the ground water at well No. 5 (which is located in cell 2) dropped only half as much as the other two wells. Cells 2N and 2S, and well No. 5 are located at the toe of the slope adjacent to the uplands. It is probable that the declining ground water is being recharged at the toe of the slope. As a result, tree vigor in these cells has not been greatly affected. In contrast, the water table below the remaining cells F.as dropped >2.0 feet and tree vigor declined accordingly. The water table at control Transect 4 has changed about 0.4 feet, and here the tree vigor has remained constant (see Figure 4). This observed correspondence between ground water and tree vigor holds true for Transects 1 and 3. We have included photographs to convey a visual image of the observed decline in vigor. Photograph A shows the low vigor canopy at Transect 2. Photograph B illustrates die back of individual branches on trees within transect 2. In contrast, Photograph C illustrates the healthy canopy of control Transect 4 (also refer to Figure 4}. An early response of trees to moisture stress is loss of leaf area, followed by crown die-back as the stress becomes more severe. Ultimately, the tree may die. As we have observed at Transect 2, cottonwood trees have demonstrated appreciable branch die-back. It is not known whether the mature cottonwoods at this site will die or be able to adjust to the observed decline in ground water and re-establish sufficient contact with the water table. We have recently purchased a Pentax Total Station which stores survey data in a data logger that can be down-loaded directly into a computer file or Geographic Information System (GIS). Once we become familiar with this machine, we will be able to traverse survey the four transects to tie them all together and relate them to a common benchmark. This machine will also allow us to quickly resurvey each transect to note any channel and associated geomorphic changes related to sand mining activities. We did not camp at the site this Spring in order to capture additional flow data. However, by monitoring our crest stage and staff gages and rain gages (rain gages were installed at the beginning of July), we feel we did not miss any significant flow events. On October 1, 1992, we met with Robert Zebrowski from the State Soil Conservation Board. We gave him a tour of Transects 2 and 3. He was able to see the mining activity and the overall condition of the cottonwoods. Robert suggested that we have a meeting this winter to discuss observations, accomplishments and future work at the Coal Creek site. He suggested that the sand mining company be included. He also mentioned the possibility of invitirn3 the Colorado Division of Wildlife, the State Land Soard, Colorado State University (they are beginning a Leafy Spurge control experiment at the site), .end any other agencies that might be interested.