Annual South American forest loss estimates based on passive microwaveremote sensing (1990–2010)

[摘要] Consistent forest loss estimates are important to understand the role offorest loss and deforestation in the global carbon cycle, for biodiversitystudies, and to estimate the mitigation potential of reducing deforestation.To date, most studies have relied on optical satellite data and new effortshave greatly improved our quantitative knowledge on forest dynamics.However, most of these studies yield results for only a relatively shorttime period or are limited to certain countries. We have quantifiedlarge-scale forest loss over a 21-year period (1990–2010) in the tropicalbiomes of South America using remotely sensed vegetation optical depth (VOD).This passive microwave satellite-based indicator of vegetation watercontent and vegetation density has a much coarser spatial resolution thanoptical data but its temporal resolution is higher and VOD is not impactedby aerosols and cloud cover. We used the merged VOD product of the AdvancedMicrowave Scanning Radiometer (AMSR-E) and Special Sensor Microwave Imager (SSM/I)observations, and developed a change detection algorithm to quantifyspatial and temporal variations in forest loss dynamics. Our resultscompared reasonably well with the newly developed Landsat-based GlobalForest Change (GFC) maps, available for the 2001 onwards period(r² =  0.90 when comparing annual country-level estimates). This allowedus to convert our identified changes in VOD to forest loss area and computethese from 1990 onwards. We also compared these calibrated results to PRODES(r² =  0.60 when comparing annual state-level estimates). We found thatSouth American forest exhibited substantial interannual variability withouta clear trend during the 1990s, but increased from 2000 until 2004. After2004, forest loss decreased again, except for two smaller peaks in 2007 and2010. For a large part, these trends were driven by changes in Brazil, whichwas responsible for 56 % of the total South American forest loss area overour study period according to our results. One of the key findings of ourstudy is that while forest loss decreased in Brazil after 2005, increases inother countries partly offset this trend suggesting that South Americanforest loss as a whole decreased much less than that in Brazil.

[学科分类] 地球化学与岩石