LONG-TERM PLANT COMMUNITY RESPONSES TO TOPSOIL REPLACEMENT DEPTH ON RECLAIMED MINED LAND

Abstract

The use of topsoil on reclaimed mine lands may enhance plant community development and influence reclamation success. This study assessed the long-term (after 24 years) effects of different topsoil replacement depths (0, 200, 400, and 600 mm) on plant community cover, production, and diversity at a research site established in 1977 in south-central Wyoming. Plant species richness (number of species), canopy cover, aboveground biomass, and diversity were evaluated at the four topsoil depths in 2001. Plants were clipped, by species, to obtain mean biomass and to calculate importance values. Shannon-Weiner diversity indices were calculated for each topsoil depth. Species richness was highest (7.5) at the zero topsoil depth and lowest (5.6) at the 600 mm topsoil depth. Total canopy cover was greatest (average 26.7%) at 400 and 600 mm of topsoil and least (21.5%) at the zero topsoil depth. Seeded species canopy cover and seeded species biomass were also greatest at the 400 mm topsoil depth. Total biomass was similar for the 400 (734 kg/ha) and 600 mm (727 kg/ha) topsoil depths and lower but similar at the 200 mm depth (506 kg/ha) and 0 mm depth (513 kg/ha). Plant species richness and diversity index were highest at 0 mm (7.5 and 2.36, respectively) and lowest at 600 mm (5.6 and 1.87, respectively) of topsoil. Number of species and diversity decreased as topsoil depth increased. Increased plant biomass at the 400 and 600 mm depths and increased diversity at the 0 and 200 mm topsoil depths, indicate that variable replacement depths of topsoil can enhance reclamation success through greater species diversity and by creating a greater mosaic of vegetation. However, the reduced cover observed at these shallower topsoil depths may not be adequate to protect the soil from erosion.