The Amazon forest is a vital component of the global carbon cycle, contributing to ca. 16% of the terrestrial carbon sink. Tree mortality, the principal mechanism whereby forests lose biomass, has increased across the Amazon. This phenomenon has been attributed largely to an increase in the frequency and intensity of droughts and to the intensification of competition, as a consequence of greater tree growth stimulated by higher CO2concentrations. Analysing the trends in mortality for different taxa allows us to test the contribution of these different drivers to the rise in tree mortality. Droughts are expected to kill drought-vulnerable, large, and light wood density taxa. Increased competition is likely to affect slow growth, understory taxa. We assess data from over 30 years of forest monitoring across the Amazon to investigate the changes in mortality across different taxa, providing a greater understanding of the drivers of increased tree mortality across the basin.
Results/Conclusions
The proportion of dead trees across different taxa has changed across the Amazon forest. We show an increase in the mortality of drought-vulnerable trees, particularly in those areas where dry climatic events have intensified over the last 30 years. However, the proportion of large taxa within the dead trees has not changed over the length of this study. We also observed indications of increasing competition-driven mortality represented by a decrease in abundance of slow-growth shade-tolerant species. A suite of mechanisms, varying regionally in importance, are acting synchronically to drive recent increases in tree death across Amazonia.