Organic Carbon Stock and their Dynamics in Rehabilitation Ecosystem Areas of Post Open Coal Mining at Tropical Region

Abstract

Exploitation of open coal mining in tropical forest ecosystem is drastically leading to land degradation and damages. Rehabilitation of extremely degraded areas through re-vegetation by fast growing species is expected to speedily recover their dynamic of organic-carbon stocks. The purposes of the study were to compare carbon stock in the aboveground biomass, understorey, litters, and soil organic under land use changes areas of open coal mining areas. The study was conducted in the coal mine concession area of PT. Berau Coal, at Site Binungan in Berau, East Kalimantan, Indonesia from September 2013 to October 2014. Data were collected from 10 plots representing ecosystem dynamics of coal mining land, consisting of: secondary forest, degraded forest; non-active mining pits; backfilling post-mining; re-vegetation forest by 2 years-old Johar (Senna siamea) stand; 1, 3 and 7 years-old Sengon (Paraserianthes falcataria); mixed forest 7 years-old Sengon (Paraserianthes falcataria) and 3 years-old meranti (Shorea sp.), and mixed forest of 9 years-old mangium (Acacia mangium) and 2.6 years-old Shorea sp. Allometric method was used to calculate the aboveground biomass and their carbon stocks. Destructive method was used to obtain the biomass of understorey, litters, and soil organic carbon. The re-vegetation programs with fast growing species after 9 year rehabilitation at post-open-mining land in tropical areas were able to restore aboveground biomass at two-thirds of previous secondary forest ecosystem. Understorey biomass in the 1-9 years-old of fast growing species were ranges at 0.19-0.95 Mg C.ha-1. Carbon stocks in the litter of 7-years-old sengon re-vegetation area were higher than that of natural forest, because of their supply from litterfall and understorey. Soil organic carbon in re-vegetation areas of 9-years-old Acacia mangium stand was 23.2 Mg.ha-1, almost equal to the value at the former secondary forest (28.5 Mg.ha-1), whereas its value during land clearing just only 4.3 Mg.ha-1. Environmental restoration in open coal mining areas through re-vegetation by fast growing plantation will restore their biomass and carbon stocks, nearly similar to their former secondary forest conditions.