INFLUENCE OF TOPSOIL DEPTH ON PLANT COMMUNITY DYNAMICS OF A SEEDED SITE IN NORTHWEST COLORADO

Reclaiming mined land to a diverse and productive ecosystem requires s pecific decisions about topsoil depth, tillage, fertilization, and sel ection of appropriate plant species. However, little published informa tion exists that provides evidence as to which reclamation practices a re effective or necessary over the long term. This study was begun in 1980 to evaluate the effects of soil depth and soil and spoil manipula tions on seeded range vegetation. The study site was located at a surf ace coal mine in northwest Colorado at an elevation of 1980 m. The exp erimental design included four topsoil depths (15, 30, 45, and 60 cm) and five different combinations of ripping, disking, and fertilization with phosphorus. Aboveground production and canopy cover were estimat ed yearly for the first 5 years of the study and then 10 years after s eeding, to provide short- and long-term information on the effectivene ss of the reclamation treatments being tested. Aboveground production and canopy cover at the end of the study were no different between the shallowest and deepest topsoil depths. However deeper topsoil depths were associated with a plant community that was dominated by grasses, while the shallower topsoil depths supported plant communities that we re more diverse and had significantly greater forb production and shru b density. It appears, after 10 growing seasons at this mine site, tha t a thin layer of topsoil (15 cm) over non-toxic spoil is sufficient f or the establishment and continued productivity of rangeland vegetatio n.