Abstract
The responses of tropical forests to environmental change are critical uncertainties in predicting the future impacts of climate change. The positive phase of the 2015-2016 El Niño Southern Oscillation resulted in unprecedented heat and low precipitation in the tropics with substantial impacts on the global carbon cycle. The role of African tropical forests is uncertain as their responses to short-term drought and temperature anomalies have yet to be determined using on-the-ground measurements. African tropical forests may be particularly sensitive because they exist in relatively dry conditions compared with Amazonian or Asian forests, or they may be more resistant because of an abundance of drought-adapted species. Here, we report responses of structurally intact old-growth lowland tropical forests inventoried within the African Tropical Rainforest Observatory Network (AfriTRON). We use 100 long-term inventory plots from six countries each measured at least twice prior to and once following the 2015-2016 El Niño event. These plots experienced the highest temperatures and driest conditions on record. The record temperature did not significantly reduce carbon gains from tree growth or significantly increase carbon losses from tree mortality, but the record drought did significantly decrease net carbon uptake. Overall, the long-term biomass increase of these forests was reduced due to the El Niño event, but these plots remained a live biomass carbon sink (0.51 ± 0.40 Mg C ha-1 y-1) despite extreme environmental conditions. Our analyses, while limited to African tropical forests, suggest they may be more resistant to climatic extremes than Amazonian and Asian forests.
Highlights
The responses of tropical forests to environmental change are critical uncertainties in predicting the future impacts of climate change
Tropical forests are a critical component of the global carbon cycle because they are extensive [1], carbon dense [2], and highly productive [3]. Consistent impacts on these forests can have global consequences. Their global importance is seen via atmospheric measurements of CO2, showing a nearneutral exchange of carbon across the terrestrial tropics; the large carbon losses from deforestation and degradation are offset by the significant carbon uptake from intact tropical forests and tropical forest regrowth [4]
Ground observations of structurally intact old-growth tropical forests show this uptake, with forest biomass carbon increasing across remaining African [5, 6], Amazonian [7], and Asian [8] forests
Summary
The responses of tropical forests to environmental change are critical uncertainties in predicting the future impacts of climate change. The long-term biomass increase of these forests was reduced due to the El Niño event, but these plots remained a live biomass carbon sink (0.51 ± 0.40 Mg C ha−1 y−1) despite extreme environmental conditions. Across 100 long-term plots, record high temperatures did not significantly reduce carbon gains from tree growth or significantly increase carbon losses from tree mortality. Ground observations of structurally intact old-growth tropical forests show this uptake, with forest biomass carbon increasing across remaining African [5, 6], Amazonian [7], and Asian [8] forests. Recent analyses of tropical forest plot data showed increased temperatures over the prior 5 y were associated with lower levels of carbon uptake from tree growth and higher levels of carbon loss from tree mortality [6]. With high temperature anomalies, we expect reduced tree growth and increased tree mortality
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