Amazon forest response to repeated droughts

The Amazon Basin has experienced more variable climate over the last decade, with a severe and widespread drought in 2005 causing large basin-wide losses of biomass. A drought of similar climatological magnitude occurred again in 2010; however, there has been no basin-wide ground-based evaluation of effects on vegetation. We examine to what extent the 2010 drought affected forest dynamics using ground-based observations of mortality and growth from an extensive forest plot network. We find that during the 2010 drought interval, forests did not gain biomass (net change: -0.43Mgha(-1), confidence interval (CI): -1.11, 0.19, n=97), regardless of whether forests experienced precipitation deficit anomalies. This contrasted with a long-term biomass sink during the baseline pre-2010 drought period (1998 to pre-2010) of 1.33Mgha(-1)yr(-1) (CI: 0.90, 1.74, p<0.01). The resulting net impact of the 2010 drought (i.e., reversal of the baseline net sink) was -1.95Mgha(-1)yr(-1) (CI:-2.77, -1.18; p<0.001). This net biomass impact was driven by an increase in biomass mortality (1.45Mgha(-1)yr(-1) CI: 0.66, 2.25, p<0.001) and a decline in biomass productivity (-0.50Mgha(-1)yr(-1), CI:-0.78, -0.31; p