Successional trends in bauxite minesites rehabilitated using three topsoil return techniques

Alcoa of Australia Limited has a programme of reafforestation of mined areas in the southwest of Western Australia. One of the aims of this programme is to re-establish forest plant communities which are compatible with long term forest land uses. In this study, successional trends of understory vegetation in 6–7-year-old bauxite minesites, revegetated using three topsoil return techniques, were examined. These techniques were double stripping (where the top 50 mm topsoil was replaced fresh), direct whole return (top 50 mm and underlying overburden both replaced fresh, but mixed) and stockpilling (both top 50 mm and overburden stockpilled together). At ages 4 years and 7 years the double stripping technique produced a vegetation community most similar in species composition to an unmined forest control. For all three topsoil return techniques there were no consistent trends in species richness (number of species) or diversity (Shannon—Weiner diversity index) from year 4 to year 7. This was interpreted as indicating conflicting trends during this period. An increase in the number of species occurred due to recruitment from surrounding forest, while a decreasing trend was probably due to tree canopy closure or increased interspecific competition. At year 7 the double stripped plot was the most similar to the native forest control in terms of physical height structure and cover occupied by individual understory species. By the age of 6–7 years there was no marked tendency for any species which initially colonised the pits to decrease in abundance. The results indicated that both fresh topsoil return and seedling are important techniques for introducing species which do not readily colonise minesites.