Estimation and Assessment of Carbon Sequestration Stocks in Topsoils of Reclaimed and Revegetated Mined-Land in Mineral Extraction Site in Bunawan, Davao City

Carbon (C) emissions from mining and industrial activities can potentially contribute to global warming. To compensate for CO2 released into the atmosphere increased by mines, an independent secondary forest assessment was carried out on reclaimed post-mining land based on its natural mode of atmospheric sequestration. This study aimed to explore the potential C sequestration activity of reclaimed post-mining land with 3-20 years secondary reforestation. This site-specific study was conducted in 47 ha of reclaimed mining land at Bunawan, Davao City of Holcim Mining and Development Corporation. Based on the vegetation types, the study areas were divided into five (5) different locations. The prevalent vegetation was bamboo (Fargesia rufa), Falcata (Paraserianthes falcataria), Lawaan (Shorea contorta Vidal) and Narra (Pterocarpus indicus). Topsoil grab sampling methods were performed in three trials in three replications. Soil pH, bulk density and percentage of organic carbon (percent organic carbon) was analysed from the test samples applying routine laboratory methods. The study found the pH of topsoils from the five sites to be 5.9-6.0 in the range. This is an advantageous condition as most of the plants are good in pH at 6.0 - 7.0, which is moderately acidic to neutral. Bulk density values of 0.862-1.069 g/cm3 might reflect soil high nutrient supply. Site organic carbon concentration was in the range of 2.04-3.00% which reflects the cumulative carbon sequestered potential 429.94Mg/ha and on average 86.0Mg/ha per area. Land with the most sequestration of carbon was recorded during the 20 years of reforestation when Lawaan (Shorea contorta Vidal) and Narra (Pterocarpus indicus) prevailed vegetation. According to the obtained studies it can be inferred that CO2 flux increases with the aging time of the planting process. The recommendations for protecting previously reclaimed mined areas to be further improved with regrading, topsoiling, and plantation are as follows: to enhance initial soil formation as well as to increase the terrestrial C pool on reclaimed fields.