REP36304 - Laserfiche WebLink

Home Browse Search

dominated by herbaceous species appeaz to respond much more rapidly to changes in the ambient precipitation regime than those communities dominated by shrubs or trees. Mean total vegetation cover was variable this season ranging from 33.40 percent to 50.20 percent (Table li). The areas exhibiting the lowest mean total vegetation cover during the 1999 sampling were the 1995 reclamation areas with 33.40 percent total vegetative cover. The 1998 reseeded or interseeded areas exhibited the highest level of total vegetation cover with 46.40 percent. This result is not unexpected given the fact that the 1998 areas had been previously seeded to the permanent revegetation mix and some growth had already developed. HERBACEOUS PRODUCTION As with vegetation cover, total herbaceous production was quite variable during the 1999 growing season (Table 11). Mean herbaceous production ranged from 67.44 g/m2 to 127.05 g/m2. The 1995 reclamation areas exhibited the highest mean herbaceous production and the 1998 reseeded or interseeded areas exhibited the lowest mean herbaceous production. Interestingly, mean herbaceous production on the Osgood sand reference area dropped 21.0 percent from the 1998 herbaceous production level. The 1995 reclamation areas experienced a 16.9 percent increase during the same time period. Perennial grasses dominated total herbaceous production in the two oldest vegetation communities, the Osgood sand reference area and the 1995 reclamation areas, accounting for 89.5 percent and 72.1 percent of the total herbaceous production, respectively. In the remaining areas sampled, lifeform contributions to the herbaceous production were nearly equally distributed between perennial grasses, annual forbs, and perennial forbs (1997 reclamation areas), or perennial grasses, annual grasses, and annual forbs (1998 reseeded or in[erseeded areas). These apparent discrepancies may be explained by the large contributions of Bromus ieclorum, Helian~hus annuus, and Ambrosia psiloslachya in the younger areas. The increased levels of early season precipitation undoubtedly aided in the development of these cool season species. SPECIES COMPOSITION The Colorado Division of Minerals and Geology considers species composition of the revegetated and reclaimed areas to be an indicator of successful vegetation establishment and a diverse vegetation community. A standard has been set by CDMG for the evaluation of species composition at [he Keenesburg Mine. To be judged successful, at final bond release, this standard requires that, "the species composition on the reclaimed area is such that there are at least seven perennial species of which four are warm season grasses and one is a forb. No one component of the above species should comprise greater than 40% relative importance nor less than 3% relative importance. Relative importance will be measured by calculating relative cover of the revegetation species. Vegetation species which may be used in the calculation of species composition may be any plant species not defined as a noxious or prohibited plant species, and may be native _17_