Abstract
SummaryOver recent decades, biomass gains in remaining old-growth Amazonia forests have declined due to environmental change. Amazonia’s huge size and complexity makes understanding these changes, drivers, and consequences very challenging. Here, using a network of permanent monitoring plots at the Amazon–Cerrado transition, we quantify recent biomass carbon changes and explore their environmental drivers. Our study area covers 30 plots of upland and riparian forests sampled at least twice between 1996 and 2016 and subject to various levels of fire and drought. Using these plots, we aimed to: (1) estimate the long-term biomass change rate; (2) determine the extent to which forest changes are influenced by forest type; and (3) assess the threat to forests from ongoing environmental change. Overall, there was no net change in biomass, but there was clear variation among different forest types. Burning occurred at least once in 8 of the 12 riparian forests, while only 1 of the 18 upland forests burned, resulting in losses of carbon in burned riparian forests. Net biomass gains prevailed among other riparian and upland forests throughout Amazonia. Our results reveal an unanticipated vulnerability of riparian forests to fire, likely aggravated by drought, and threatening ecosystem conservation at the Amazon southern margins.
Highlights
The single largest repository of biodiversity and biomass carbon on Earth is the Amazon forest, still covering almost 5.3 million km2 and representing a uniquely large and relatively contiguous tropical forest (Aragão et al 2014)
We aimed to: (1) estimate the long-term biomass change rate; (2) determine the extent to which forest changes are influenced by forest type and fire; and (3) use these results to evaluate drivers of biomass change and to assess the threat to forests from upcoming environmental change in the ZOT
Despite substantial plot-to-plot variation in biomass dynamics (5.43 standard deviations; Supplementary Fig. S2(a) and S2(b)), overall changes in net aboveground biomass (AGB) among plots remained at balance over the monitored period (V = 260, p = 0.584)
Summary
The single largest repository of biodiversity and biomass carbon on Earth is the Amazon forest, still covering almost 5.3 million km and representing a uniquely large and relatively contiguous tropical forest (Aragão et al 2014). The mechanisms related to this decline involve both shortening carbon residence times due to increased mortality rates and levelling off of growth rate increases (Brienen et al 2015). These long-term basin-wide changes are consistent with drought sensitivity and multiple anthropocentric environmental threats (Phillips et al 2009, Aragão et al 2014, Gatti et al 2014, Anderson et al 2015). The potential impact of climate change and its interaction with anthropogenic disturbances (e.g., fragmentation and fire) on South American forests remains highly uncertain (Aragão et al 2014, Tollefson 2016), and how these ecosystems will feed back on climate change is poorly understood (e.g., Davidson et al 2012, Aragão et al 2014)
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