Effects of reclamation effort on the recovery of ecosystem functions of a tropical degraded serpentinite dump site

Surface mining or other disturbing operations on ultramafic outcrops degrade soil conditions and decrease major ecosystem functions in those habitats. Human disturbances exacerbate the harsh conditions of some ultramafic soils, making recovery more difficult. Recovery of ecosystem functions of disturbed areas may vary from passive to active reclamation measures, depending on the starting situation, available resources and expected outcomes. In this study, three treatments (topsoil application, topsoil + non-compacted, and topsoil + non-compacted + organic amendment), representing a gradient of increasing reclamation effort, were tested for the reclamation of a tropical ultramafic Spolic Technosol in Sabah (Malaysia). Soil treatments were tested at the mesocosm-scale for 12 months, and drainage water fluxes, evolution of soil physicochemical parameters, soil microbial activities and spontaneous plant colonisation, diversity and growth were monitored along the duration of the experiment. The results show that application of topsoil improved the plant biomass and water filtration functions in the non-reclaimed sites, with no additional benefit from lesser compaction. The most intensive treatment (topsoil + non-compacted + organic amendment) gave the best improvements in nutrient cycling and biomass production functions, but with a reduction of water filtration function, due to an increase in soluble concentrations and cumulative fluxes of nickel. Introduced species were dominant in the vegetation colonising the mesocosms, and therefore planting of selected native species will be necessary to create habitats for native biodiversity. This information will be useful to select a strategy for the recovery of degraded tropical serpentinite quarries and dump sites.