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IV. DISCUSSION AND CONCLUSIONS Areas revegetated in 1995 and 1997, and those reseeded or interseeded in 1998 were quantitatively sampled in 1999 to evaluate revegetation establishment for monitoring purposes, and identify any areas which require implementation of additional measures to ensure long term revegetation success. The Osgood sand reference area was also quantitatively sampled to provide the revegetation success criteria values for total vegetation cover and total herbaceous production for the reclaimed areas governed by the requvements of CDMG Rule 4.15.8. 1999 PRECIPITATION REGIME The climate of the mine and surrounding area is characterized by a wide temperature fluctuation; from below freezing in winter, to very warm in the summer months. Precipitation in the azea is provided by weather systems originating in the Gulf of Mexico and is most frequent and reliable during the spring and late summer months (Table 10). Coors Energy Company has collected precipitation data at the mine for a number of years. This data represents the most complete record of precipitation from the mine area. Table 10 presents a summary of precipitation data collected from 1993 through 1999, corresponding with the most recent vegetation monitoring. A review of the data illustrates that precipitation is lowest during the autumn and winter months (October through March) and higher from spring through late summer. The months with the highest average precipitation are May and June. Based on the 1993-1999 data, average yearly precipitation was calculated. Additionally, an average "growing season" precipitation was calculated based on the months with reliable precipitation which was most likely to impact vegetation growth during a specific growing season (January-July). From this average, comparisons of individual yearly precipitation and its effect on specific growing seasons can be made. Total January-July precipitation for the 1999 season was 11.67 inches. This translates into a 35.2 percent positive departure from the January-July precipitation average and a 40.6 percent increase from the same period in 1998. VEGETATION COVER For the two areas where quantitative cover data is present from prior yeazs (Osgood sand reference area and 1995 reclamation areas), the 1999 growing season revealed an increase in total vegetation cover. The Osgood sand reference area showed an 11.6 percent increase while the 1995 reclamation areas showed a 24.2 percent increase from the 1998 season (Table 11). This increase may be attributable to the signiScant increase in precipitation early this year, particularly in April and May. As has been noted previously, the scale of the response to the increase in precipitation varied significantly between the reference area and the 1995 reclamation areas. This can likely be attributed to the difference in lifeform dominance in each of these communities. Vegetation communities -16-