Reply to Wernick et al.: Global scale quantification of forest change

Abstract

Our results, reported in Hansen et al. (1) in a recent issue of PNAS, illustrate the value of earth observation data sets in generating internally consistent quantifications of land cover change, specifically, gross forest cover loss at the global scale. In that article, we state that our results are limited to this dynamic and that a more complete characterization of forest change would include forest cover gain and the proximate drivers of change. Wernick et al. (2) take issue with (i) our purported dismissal of other data and findings and (ii) the lack of reforestation/carbon uptake analyses. Concerning existing global data sets on forest extent and change, the issues regarding definitions and the difficulty in producing global scale syntheses is well described by others and referenced in our paper (3, 4). We believe that improved consistency in both definitions and methods is needed to advance global forest monitoring. Our results are a step in that direction and illustrate the value of deriving internally consistent and directly comparable results at the global scale. Our study does not replace or supersede other results, and we do not present our result as “the only one based on sound data.” Our results are unique and limited to the gross forest cover loss dynamic.