Cropland expansion drives vegetation greenness decline in Southeast Asia

Abstract

Abstract. Land-use and land-cover change (LUCC) is a key factor in determining regional vegetation greenness, impacting terrestrial carbon, water, and energy budgets. As a global LUCC hot spot, Southeast Asia has experienced intensive cropland and plantation expansion over the past 50 years; however, the impacts of these changes on the regional greenness have not been elucidated. Here, we harmonized multiple land-cover datasets, and used the satellite-derived leaf area index (LAI) in combination with a machine learning approach to quantify the impacts of LUCC on vegetation greenness in insular Southeast Asia (i.e. Peninsular Malaysia, Sumatra, and Borneo). We found that the regional LAI shows almost no trend (0.04 × 10−2 m2 m−2 yr−1) from 2000 to 2016: the net effect of an increased LAI (+5.71 × 10−2 m2 m−2 yr−1) due to CO2 fertilization is offset by a decreased LAI mainly due to cropland expansion (−4.46 × 10−2 m2 m−2 yr−1). The impact of croplands on greenness in Southeast Asia contrasts with that in India and China. Meanwhile, oil palm expansion and climate change induced only small decreases in the LAI in Southeast Asia (−0.41 × 10−2 and −0.38 × 10−2 m2 m−2 yr−1, respectively). Our research unveils how the LAI changes with different LUCC processes in Southeast Asia and offers a quantitative framework to assess vegetation greenness under different land-use scenarios.