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

M J E Van Marle,R A M De Jeu,G R Van Der Werf,Y Y Liu

doi:10.5194/bg-13-609-2016

Abstract

Abstract. Consistent forest loss estimates are important to understand the role of forest loss and deforestation in the global carbon cycle, for biodiversity studies, and to estimate the mitigation potential of reducing deforestation. To date, most studies have relied on optical satellite data and new efforts have greatly improved our quantitative knowledge on forest dynamics. However, most of these studies yield results for only a relatively short time period or are limited to certain countries. We have quantified large-scale forest loss over a 21-year period (1990–2010) in the tropical biomes of South America using remotely sensed vegetation optical depth (VOD). This passive microwave satellite-based indicator of vegetation water content and vegetation density has a much coarser spatial resolution than optical data but its temporal resolution is higher and VOD is not impacted by aerosols and cloud cover. We used the merged VOD product of the Advanced Microwave Scanning Radiometer (AMSR-E) and Special Sensor Microwave Imager (SSM/I) observations, and developed a change detection algorithm to quantify spatial and temporal variations in forest loss dynamics. Our results compared reasonably well with the newly developed Landsat-based Global Forest Change (GFC) maps, available for the 2001 onwards period (r2 = 0.90 when comparing annual country-level estimates). This allowed us to convert our identified changes in VOD to forest loss area and compute these from 1990 onwards. We also compared these calibrated results to PRODES (r2 = 0.60 when comparing annual state-level estimates). We found that South American forest exhibited substantial interannual variability without a clear trend during the 1990s, but increased from 2000 until 2004. After 2004, forest loss decreased again, except for two smaller peaks in 2007 and 2010. For a large part, these trends were driven by changes in Brazil, which was responsible for 56 % of the total South American forest loss area over our study period according to our results. One of the key findings of our study is that while forest loss decreased in Brazil after 2005, increases in other countries partly offset this trend suggesting that South American forest loss as a whole decreased much less than that in Brazil.

Highlights

There are large uncertainties in the spatial and temporal patterns of forest loss and associated fluxes of carbon in the tropical ecosystems (Grainger, 2008; Hansen et al, 2010; Malhi, 2010; Pan et al, 2011)
We show how the merged vegetation optical depth (VOD) product can be used to estimate forest loss for South America on a countrylevel scale, but we point towards limitations of our approach and the data set
This is in line with our trends and time series (Fig. 7, Table 2) in which both VOD and Global Forest Change (GFC) show an increasing trend for Argentina over 2001–2010, whereas a decreasing trend over that time period occurred in Brazil (Table 2)

Summary

Introduction

There are large uncertainties in the spatial and temporal patterns of forest loss and associated fluxes of carbon in the tropical ecosystems (Grainger, 2008; Hansen et al, 2010; Malhi, 2010; Pan et al, 2011). Forest loss can be either natural, for example due to wind-throw or natural fires, or anthropogenic, usually labelled deforestation. Deforestation carbon emissions are a significant but declining fraction of total anthropogenic CO2 emissions (van der Werf et al, 2009). More than half of the total forest carbon is stored in tropical intact forests, of which more than 50 % is stored in living biomass, about a third in the soil, with the remaining carbon being stored in dead wood and litter (Pan et al, 2011). In South America, deforestation is mainly caused by the expansion of agriculture and the area

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