Assessment of fire contribution to forest loss in sub-Saharan Africa using medium-resolution BA

Deforestation represents one of the major challenges of the current era as it constitutes an imminent threat to the forest carbon sink offsetting the different sources of greenhouse gas (GHG) emissions. Fire is highly contributing to forest loss and degradation as a driver (i.e. wildfires) and a clearing tool (e.g. slash-and-burn agriculture). However, fire impacts were mainly analysed at coarse spatial resolutions, and therefore estimations are deemed to be very conservative because of the high omission errors in global BA products. In this study, we focus on sub-Saharan Africa (SSA), which represents the region most affected by fires globally. We analysed fire-related forest loss at 20 m resolution based on FireCCISFD datasets available for 2016 and 2019, in combination with the Global Forest Cover (GFC) maps derived from medium-resolution sensors (Sentinel 2 and Landsat, respectively). These estimations were compared to the ones of two global BA products derived from the MODIS sensor, namely MCD64A1 (Collection 6) and FireCCI51. We found that fires are a precursor of forest loss, as burned areas had more than twice the chance to be lost than unburned ones during the two study years, and that on average, fires were directly involved in almost half of forest losses in SSA (46 ± 3.80% in 2019 and 47 ± 4.21% in 2016). Depending on biomes and the year of study, fire-related forest cover loss ranged from 32 ± 1.83% to 75 ± 3.65%. In general, the subtropics dominated by Tropical Savanna and Dry Tropical Forest exhibit the highest contributions of fire, whereas the tropical zone, where Moist Tropical Forest is prevailing, showed lower contributions due to the lower fire activity. Fragmentation, as well as fire season, were found to be drivers of forest loss as the majority of these losses occur in fragmented areas close to forest edge (< 320 m) and in late fire season. We conclude that the use of medium-resolution BA products to assess fire impacts in tropical ecosystems is crucial.