| A project was initiated in 1998 to investigate the effect of varying topsoil depths on various soil and plant parameters on a coal mine in northeastern Wyoming. Soil and vegetation information was collected from 2000 through 2002. Reclaimed treatments included three replacement topsoil depths (15, 30 and 56 cm). Slope positions within two native reference areas were assumed to be reclaimed treatment comparisons. Dependent variables included pH, electrical conductivity (EC), sodium adsorption ratio (SAR), total cover, total vegetation cover, total number of species and average number of species (based on cover sampling) and above-ground production. Results over the three year study indicated a slight reduction in pH, EC and SAR within the upper 15 cm depth in the reclaimed topsoil treatments with a general increase of EC and SAR in the lower portion of the replaced soil profile. Reduced EC was noted in the backfill below the 15 cm reclaimed treatment in 2001. Soil pH, EC and SAR were significantly higher in the upper 30 cm of the reclaimed soil profile than the native reference areas. Inherent pH, EC and SAR gradients in the native profiles were not present in the reclaimed treatments. Species richness was highest in the 30 cm reclaimed treatment and, overall, there was an increased number of perennial forbs in the 30 cm reclaimed treatment. Shannon-Wiener index (H′) values in 2001 were significantly greater in the 30 cm reclaimed treatment. On a landscape basis, a mosaic of variable topsoil depths, collectively provided generally higher diversity than the mandated 56 cm depth. Total vegetation cover on the 56 cm reclaimed treatment was significantly greater than the 15 cm treatment. Reclaimed area production exceeded the two native reference areas after three years of growth. In summary, from observations made at the North Antelope/Rochelle Mine (NARM), a mosaic of different topsoil depths, including the shallow 15 and 30 cm depths, creates the broadest range of vegetation response under a standard regime of revegetation practices. A limited number of treatment differences may be a manifestation of the low overall precipitation conditions, relatively young age of the reclaimed area and lack of levels of pH, EC and SAR detrimental to plant growth in the backfill. |
