Preprints
https://doi.org/10.5194/esd-2024-5
https://doi.org/10.5194/esd-2024-5
01 Feb 2024
 | 01 Feb 2024
Status: this preprint is currently under review for the journal ESD.

The impacts of elevated CO2 on forest growth, mortality and recovery in the Amazon rainforest

Yitong Yao, Philippe Ciais, Emilie Joetzjer, Wei Li, Lei Zhu, Yujie Wang, Christian Frankenberg, and Nicolas Viovy

Abstract. The Amazon rainforest plays a crucial role in global carbon storage, but a minor destabilization of these forests could result in considerable carbon loss. Among the external factors affecting vegetation, elevated CO2 (eCO2) levels have long been anticipated to have positive impacts on vegetation, including direct photosynthesis / productivity enhancement and increasing water use efficiency. However, the overall impact of eCO2 on the net carbon balance, especially concerning tree mortality-induced carbon loss and recovery following extreme drought events, has remained elusive. Here, we use a process-based model that couples physiological CO2 effects with demography and drought mortality / resistance processes. The model was previously calibrated to reproduce observed drought responses of Amazon forest sites. The model results, based on factorial simulations with and without eCO2, reveal that eCO2 enhances forest growth and promotes competition between trees, leading to more natural self-thinning of the forest stands, following a growth-mortality trade-off response although the growth outweighs the tree loss. Additionally, eCO2 provides water-saving benefits, reducing the risk of tree mortality during drought episodes, although extra carbon losses still could occur due to eCO2 induced increase in background biomass density, thus ‘more carbon available to lose’ when severe droughts happen. Furthermore, we found that eCO2 accelerates the drought recovery and enhances drought resistance and resilience. These findings illuminate the intricate ways in which increasing CO2 concentrations shape forest carbon dynamics, offering valuable insights into the evolution of the Amazon rainforest.

Yitong Yao, Philippe Ciais, Emilie Joetzjer, Wei Li, Lei Zhu, Yujie Wang, Christian Frankenberg, and Nicolas Viovy

Status: open (until 14 Mar 2024)

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  • RC1: 'Comment on esd-2024-5', Anonymous Referee #1, 28 Feb 2024 reply
Yitong Yao, Philippe Ciais, Emilie Joetzjer, Wei Li, Lei Zhu, Yujie Wang, Christian Frankenberg, and Nicolas Viovy
Yitong Yao, Philippe Ciais, Emilie Joetzjer, Wei Li, Lei Zhu, Yujie Wang, Christian Frankenberg, and Nicolas Viovy

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Short summary
Elevated CO2 concentration (eCO2) is critical to shape the future path of forest carbon uptake, while large uncertainties remain in the concurrent carbon loss. Here we found that eCO2 might amplify competition-induced carbon loss, while the extent of drought-induced carbon loss hinges on the balance between heightened biomass density and water-saving benefits. This is the first time that such carbon loss responses to ongoing climate change are quantified separately over the Amazon rainforest.
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