Tropical forests are among the most diverse ecosystems in the world, completed by huge biodiversity. An expansion in natural resource extraction through open-pit mining activities leads to increasing land and tropical forest degradation. Proper science-based practices are needed as an effort to reclaim their function. This paper summarizes the existing practice of coal mining, covering the regulatory aspects and their reclamation obligations, the practices of coal mining from various sites with different land characteristics, and the reclamation efforts of the post-mining landscapes in Indonesia. The regulations issued accommodate the difference between mining land inside the forest area and outside the forest area, especially in the aspect of the permit authority and in evaluating the success rate of reclamation. In coal-mining practices, this paper describes starting from land clearing activities and followed by storing soil layers and overburden materials. In this step, proper handling of potentially acid-forming materials is crucial to prevent acid mine drainage. At the reclamation stage, this paper sequentially presents research results and the field applications in rearranging the overburden and soil materials, controlling acid mine drainage and erosion, and managing the drainage system, settling ponds, and pit lakes. Many efforts to reclaim post-coal-mining lands and their success rate have been reported and highlighted. Several success stories describe that post-coal-mining lands can be returned to forests that provide ecosystem services and goods. A set of science-based best management practices for post-coal-mine reforestation is needed to develop to promote the success of forest reclamation and restoration in post-coal-mining lands through the planting of high-value hardwood trees, increasing trees’ survival rates and growth, and accelerating the establishment of forest habitat through the application of proper tree planting technique. The monitoring and evaluation aspect is also crucial, as corrective action may be taken considering the different success rates for different site characteristics.

Opencast nickel mining is common in natural forests of Indonesia. However, rehabilitation of postmining degraded land is difficult. We investigated the effect of opencast nickel mining on soil chemical properties and the growth of two fast-growing tropical tree species, Falcataria moluccana and Albizia saman. Soil was collected from post-nickel mining land and a nearby natural forest. Soil pH, available phosphorus (P) concentration, total carbon (TC) and total nitrogen (TN) concentration, C/N ratio, cation exchange capacity (CEC), and exchangeable K, Na, Mg, Ca, Fe, and Ni concentrations were determined. Falcataria moluccana and A. saman were then grown in the collected soils for 15 weeks in a greenhouse. Shoot height and shoot and root dry weights of the seedlings were measured. The post--nickel mining soils TN, TC, available P, CEC, and exchangeable Ca and Na concentrations decreased by 98%, 93%, 11%, 62%, 85%, and 74%, respectively, in comparison with the natural forest soils. The pH of postmining soil was higher than natural forest soil. Shoot dry weight of F. moluccana seedlings grown in postmining soil was significantly ( P < 0.05 ) lower than that of seedlings grown in natural forest soil. However, there was no difference in shoot dry weight between A. saman seedlings grown in natural forest soil and postmining soil, as well as root dry weights of both species. The results indicate that opencast nickel mining decreased soil fertility, which subsequently inhibited the growth of F. moluccana and A. saman seedlings.

The remediation of opencast bauxite mines in the natural forests of Indonesia is difficult. We have investigated and contrasted the chemical characteristics of soils from natural forests and mining sites and their effects on plant growth. The soil pH, total carbon (C), nitrogen (N) and available phosphorus (P) concentrations, cation exchange capacity, C/N ratio, and exchangeable K, Na, Mg, Ca, Fe, and Ni concentrations were determined. Falcataria moluccana and Albizia saman were then grown in these soils for 15 weeks, and their shoot heights, shoot dry weights, and root dry weights determined. The post bauxite mining soils’ N, C, and available P concentrations and exchangeable Ca, Mg, and Na concentrations decreased by 75, 75.7, 15.7, 92, 100, and 52%, respectively, in comparison with the natural forest soils. The shoot and root dry weights of F. moluccana when grown in the post bauxite mining soils were also lower than those from the natural forest soils. However, there was no difference in the shoot and root dry weights of A. saman when grown in the two soil types. The results suggest that opencast mining decreases the soil fertility, which in turn inhibits the initial growth of tree seedlings, and reduces the carbon stock in the land.

The purpose of this investigation was to examine the effects of native AM fungal inoculation on the growth of Gmelina arborea, Samanea saman, Falcataria moluccana, and Enterolobium cyclocarpum under nursery and post-opencast bauxite mining field conditions. Two native AM fungi, Rhizophagus clarus and Gigaspora decipiens, were inoculated into seeds of G. arborea, S. saman, F. moluccana, and E. cyclocarpum. The seeds were sown in post-bauxite mining soil and grown in the nursery for three months. Seeds without AM inoculation were used as the control treatment. The seedlings were transplanted into a post-opencast bauxite mining field and grown for 12 months. Arbuscular mycorrhizal fungal colonization and shoot and root dry weights were measured. Under nursery conditions, G. arborea inoculated with G. decipiens increased shoot and root dry weights by 1,431 and 359 %, respectively, while shoot dry weight of E. cyclorapum inoculated with R. clarus and G. decipiens increased by 510 and 220%, respectively, in comparison with control seedlings. Root dry weight of E. cyclorapum inoculated with R. clarus increased by 224%, in comparison with control seedlings. Shoot dry weight of E. cyclorapum inoculated with R. clarus increased by 90%, in comparison with seedlings inoculated by G. decipiens. Twelve months after transplanting into post-opencast field conditions, the shoot dry weight of F. moluccana inoculated with G. decipiens was higher than that of the control seedlings by 188%. Shoot dry weight of E. cyclorapum inoculated with R. clarus and G. decipiens increased by 198% and 149%, respectively, in comparison with control seedlings. Shoot dry weight of E. cyclorapum seedlings inoculated with R. clarus was higher by 20% than that of seedlings inoculated with G. decipiens. These results show that AM fungal inoculation promotes the growth of tropical tree species on post-opencast bauxite mining land.

No abstract