Integrating Indicators of Natural Regeneration, Enrichment Planting, Above-Ground Carbon Stock, Micro-Climate and Soil to Asses Vegetation Succession in Postmining Reclamation in Tropical Forest

Open-cast mining in tropical forests causes negative impacts on biodiversity and carbon storage. Postmining reclamation is therefore imposed to recover the vegetation despite the lack of understanding which indicators can be used to monitor the progress of succession. This study proposes an integrated framework to assess the trajectory of vegetation succession in coal mining site in East Kalimantan, Borneo. We combine the indicators of floristic diversity of naturally growing terrestrial and epiphytic plants, survival and growth of enrichment planting of native plants, above-ground carbon stock of pioneer trees, and the measurements on micro-climate and soil conditions. We compare some indicators across the 9-year-old and 17-year-old reclaimed sites and the premining sites. The results showed that naturally growing vegetation at the reclaimed sites was at the early to midsuccession stages, with biodiversity indicators much lower than those at the premining areas, implying the necessity of native species planting. During a six-month monitoring, the enrichment planting of native species had high rates of survival and growth. Surprisingly, the above-ground carbon at the two reclamation sites were higher, up to six times larger, than that at the premining sites. While the micro-climates had been improved, the soils in the reclaimed sites were still in poor conditions. Our findings suggest that using single parameter to monitor the trajectory of vegetation succession in postmining reclamation can be biased, and integrating several monitoring measures would provide a much better assessment.