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Context: Tropical forests in mainland Southeast (MSEA) have important conservation values and provide critical ecosystem functioning and services. With climate change and increasing anthropogenic activities, these forests can be lost to other land use types or degraded. Objectives: We aim to understand how these forests have changed under the context of MSEA's rapidly changing physical and socioeconomic environments in recent decades. Methods: We employed satellite-derived tree cover products, primarily the MODIS-based Vegetation continuous field (VCF) data, to investigate changes in forest cover with a focus on potential forest degradation to savannah since 2000 for the four MSEA countries, i.e., Thailand, Laos, Cambodia, and Vietnam. Results: We found an overall increasing trend of savannah (defined as places with tree cover between 10 and 55%) during the period 2000–2020. However, the sources of the increased savannah area differed significantly between 2000–2009 and 2009–2020: In the earlier decade, the positive trend of the savannah area was primarily attributed to tree regeneration from grasslands; while during the more recent decade, the degradation (savannization) of forests was the major cause. Fire disturbance primarily controlled interannual variation in tree cover for the savannah gain during the period of 2000–2009, while high atmospheric water demand drove the degradation of forests during the period of 2010–2020. Conclusions: Our analysis sheds light on the understanding of changing forest landscapes in a globally important region of tropical forests, which is critical for informing land management and tropical forest protection. [ABSTRACT FROM AUTHOR]

Historical land-use practices have caused forest loss in Cambodia's Tonle Sap Lake area (TSLA), the largest freshwater lake in Southeast Asia. However, it remains unclear if this deforestation trend had continued since 2001 when the land was designated as protected areas. Using satellite imagery, we investigated forest conversion flows and fragmentation patterns in the TSLA for 1992–2001, 2001–2010, and 2010–2019, respectively. Results show substantial forest losses and fragmentations occurring at the lower floodplain where the protected areas are located until 2010, with some forest regain during 2010–2019. The land conversions indicated that forest clearing and agricultural farming were the primary causes for observed extensive forest loss during 1992–2010. Hence, despite the creating of protected areas in 2001, our findings reveal the persistence of alarming forest loss in the TSLA until 2010. On the other hand, while net forest loss has stopped after 2010, forest regain during 2010–2019 is way too small to restore the region's total forest area to even the level when the protected areas were established. Thus, more effective planning and implementations of forest management and restoration policies are needed for the TSLA. [ABSTRACT FROM AUTHOR]