Large scale reforestation of farmlands on sloping hills in South China karst

Abstract

South China karst is undergoing large scale land-use conversions driven by reforestation projects aiming at combating land degradation. However, the spatial extent of these human induced land-use changes is largely unknown. This study aims at quantifying land use changes in South China karst in the context of large scale restoration and reforestation projects. We apply an extensive field survey on land-use mapping and find that 45,406 km2 of farmland have been converted to forest, while 41,811 km2 have been deforested (likely due to timber harvest), which corresponds to a forest expansion of 6%, and an 8% contraction of farmlands. We find that the converted areas agree well with satellite observed greening trends, explaining why South China karst is considered a global hot-spot of vegetation cover increase. In total, 43% of the farmland to forest conversions have taken place on sloping hills steeper than 25° and predominantly at larger distances from settlements. However, 19,464 km2 of the steep sloping areas were still farmland in 2016, which is 15% of the total farmland in South China karst. Large scale forest dynamics are observed on sloping hills. Given the low agricultural productivity but high erosion risk, considerations regarding loss of crop production and local food security must be balanced against gains in expected provisioning of ecosystem services (e.g. carbon sequestration, timber production).