Abstract
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 the direct enhancement of both photosynthesis and productivity 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 both drought mortality and 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 forest stands. This occurs 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. However, extra carbon losses could still occur due to an eCO2-induced increase in background biomass density, leading to “more carbon available to lose” when severe droughts happen. Furthermore, we found that eCO2 accelerates drought recovery and enhances drought resistance and resilience. By delving into the less-explored aspect of tree mortality response to eCO2, the model improvements advance our understanding of how carbon balance responds to eCO2, particularly regarding mechanisms of continuous competition-induced carbon loss vs. pulses of drought-induced carbon loss. These findings provide valuable insights into the intricate ways in which rising CO2 influences forest carbon dynamics and vulnerability, offering a critical understanding of the Amazon rainforest's evolution amidst more frequent and intense extreme climate events.
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Claims 9
Claim · model-written summary
Elevated CO2 enhances Amazon forest growth in the simulations.
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Verbatim
e0“eCO2 enhances forest growth”
Claim · model-written summary
Elevated CO2 promotes competition among Amazon forest trees in the simulations.
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Verbatim
e0“eCO2 enhances forest growth and promotes competition between trees”
Claim · model-written summary
Elevated CO2 increases natural self-thinning of Amazon forest stands in the simulations.
Not reportedComparator
Verbatim
e0“eCO2 enhances forest growth and promotes competition between trees, leading to more natural self-thinning of forest stands”
Claim · model-written summary
The simulated forest growth gain outweighs the associated tree loss under elevated CO2.
Verbatim
e0“the growth outweighs the tree loss”
Claim · model-written summary
Elevated CO2 reduces the risk of Amazon tree mortality during drought through water-saving benefits.
- Taxon
- treee0
- Treatment
- eCO2e0
- Outcome
- risk of tree mortalitye0
- Direction
- reducinge0
- Qualifier
- during drought episodese0
Not reportedComparator
Verbatim
e0“eCO2 provides water-saving benefits, reducing the risk of tree mortality during drought episodes”
Claim · model-written summary
Elevated CO2 increases background biomass density, making extra carbon loss possible during severe drought.
- Taxon
- biomasse0
- Treatment
- eCO2e0
- Outcome
- background biomass densitye0
- Direction
- increasee0
- Qualifier
- when severe droughts happene0
Not reportedComparator
Verbatim
e0“extra carbon losses could still occur due to an eCO2-induced increase in background biomass density, leading to “more carbon available to lose” when severe droughts happen”
Claim · model-written summary
Elevated CO2 may increase carbon losses during severe drought because more background biomass is available to lose.
Verbatim
e0“extra carbon losses could still occur due to an eCO2-induced increase in background biomass density, leading to “more carbon available to lose” when severe droughts happen”
Claim · model-written summary
Elevated CO2 accelerates simulated drought recovery in the Amazon forest.
Not reportedComparator
Verbatim
e0“eCO2 accelerates drought recovery”
t0“the Amazon rainforest”
Claim · model-written summary
Elevated CO2 enhances simulated drought resistance and resilience in the Amazon forest.
Not reportedComparator
Verbatim
e0“eCO2 accelerates drought recovery and enhances drought resistance and resilience”
t0“the Amazon rainforest”