Effects of land-use change on carbon dynamics assessed by multi-temporal satellite imagery in a mountain watershed of Nepal

Satellite imagery from 1976, 1989, and 2003 was analysed to assess land-use change and its effect on carbon (C) dynamics in the Pokhare Khola watershed of Nepal. The soil organic carbon (SOC) pools and forest vegetation C pools were estimated using field data and Intergovernmental Panel on Climate Change (IPCC) tier 1 method. The analysis of a temporal series of satellite imagery was found to be an effective tool to determine the land-use-change dynamics in the mountain watershed. During the period 1976-2003, overall forest area decreased by 24%, with significant increase in area under cultivated lands (82%). While taking into account the individual land-use types, the areas under rainfed upland, managed dense forest, and Schima-Castanopsis forest increased by 200, 174, and 58%, respectively, with substantial decreases in both degraded forest/shrub lands (35%) and pine mixed forest (92%). The effects of land-use change on SOC pool varied according to the type of land-use change. There was a net gain in the SOC pool in the larger part of the watershed during 1976-1989, but in the period 1989-2003 a net loss was observed. Conversion from forest to cultivated lands has resulted in a severe loss of vegetation carbon. However, in the future, there will be higher vegetation carbon pools in the watershed, because a significant land area under degraded forest/shrub land and pine mixed forest has been converted to managed-dense forest and Schima-Castanopsis forest, which were shown to contain significantly higher amounts of vegetation carbon.