Quantifying forest change

Abstract

In a recent issue of PNAS, Hansen et al. (1) did an excellent job of arguing for the need for a more consistent data set to investigate changes in global forest cover. The indicator they chose, gross forest cover loss (GFCL), marks an improvement both in reproducibility and comparability. However, it does so by using data that the authors themselves state “captures only part of the global forest cover change dynamic” (p 8651). One would expect that an analogous measure of forest growth over the same period might show a gain in forest cover if data on loss were excluded. In describing the forest cover dynamic, Alig (2) comments that “Net changes (area into forest minus area out of forest) are typically much smaller than total or gross changes (area into forest plus area out of forest).”