LONG-TERM PLANT COMMUNITY DEVELOPMENT IN RESPONSE TO TOPSOIL REPLACEMENT DEPTH ON MINED LAND IN WYOMING

Effects of topsoil replacement depth on plant community development of reclaimed mined lands has been discussed for nearly three decades. Numerous research projects assessing topsoil depth effects were initiated during the 1970s. However, data collection for many of these studies was limited to 3-5 years. Plant community establishment, development, and stabilization through successional processes require considerable time. Only aboveground biomass and plant cover were reported in these short-term studies. In 2001, a research project initiated in 1977 was re-evaluated to assess the long-term effects of topsoil replacement depth (0, 20, 40 and 60 cm) on plant community development in south-central Wyoming. Percent grass cover and aboveground biomass were highest on the 40 and 60 cm topsoil depths, while forb cover was highest on the 0 and 20 cm depths. Percent bare ground was lowest on the 60 cm depth (30%) and highest on the 0 cm topsoil depth (62%). Plant species richness and diversity were significantly higher on the 0 cm topsoil depth and lowest on the 60 cm depth. Many native plant species established naturally in the abundant open space of the 0 cm topsoil replacement treatment. Variable topsoil replacement depth is a good management practice to enhance plant community diversity on reclaimed mined lands. However, placement of variable topsoil depths must consider erosion potential during the early years of reclamation. Areas of shallow topsoil should be limited to sites not prone to erosion, limited in size, and intermingled with other areas of greater topsoil replacement to ensure early stabilization and plant diversity of the reclaimed landscape.