Post-mining rehabilitation of coastal sand dunes in Zululand South Africa

In the process of dredge mining, employed since 1977 on the Zululand coast, heavy minerals are extracted from the dunes after the complete removal of the existing vegetation. The tailings are then reshaped to approximate their original contours, covered with topsoil and revegetated with a cereal cover crop, together with indigenous seeds of long-lived (woody) species. The existence of stands of different ages over a recorded period provided an opportunity to study changes in species composition and vegetation dynamics. Five random 10 × 10m quadrats were sampled in stands of age 4, 5, 7, 8, 9, 10, 11 and 12 years respectively, and cover data were used for multivariate analysis using TWINSPAN and DECORANA. Importance values of each species, and total and mean species richness were also calculated. Pre-mined and mined soil samples were analysed for trace elements, organic matter and pH. Recently rehabilitated areas of 4 to 5 years were dominated by Acacia karroo, but species richness showed a progressive increase with age of rehabilitated stands, with more woody species in the older stands and a slight decline in dominance of A. karroo. TWINSPAN classified older and younger stands into distinct groups which were related to a chronological succession gradient, also shown by the DECORANA ordination. Some soil nutrients of rehabilitated areas compared favourably with the pre-mined topsoil and subsoil, but percentage organic matter content was still higher in natural dune forests. Increases in soil nutrients suggest that nutrient retention and the establishment of substantial soil flora and fauna are occurring, providing evidence for the sustainability of the soils. From this study it appears that successional changes follow the facilitation pathway, and rehabilitation will eventually lead to the restoration of the dune forest.