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https://doi.org/10.5194/bg-2019-497
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-497
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 08 Jan 2020

Submitted as: research article | 08 Jan 2020

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This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Drought resistance increases from the individual to the ecosystem level in highly diverse neotropical rain forest: a meta-analysis of leaf, tree and ecosystem responses to drought

Thomas Janssen1, Katrin Fleischer2, Sebastiaan Luyssaert3, Kim Naudts1, and Han Dolman1 Thomas Janssen et al.
  • 1Department of Earth Sciences, Cluster Earth and Climate, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands
  • 2Land Surface-Atmosphere Interactions, Technical University of Munich, Freising, Germany
  • 3Department of Ecological Sciences, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands

Abstract. The effects of future warming and drying on tropical forest functioning remain largely unresolved. Here, we conduct a meta-analysis of observed drought responses in neotropical humid forests, focused on carbon and water exchange. Measures of leaf, tree and ecosystem scale performance were retrieved from 138 published studies conducted across 229 sites in neotropical forests. Differentiating between seasonal and episodic drought we find that; (1) during seasonal drought, the increase of atmospheric evaporative demand and a decrease of soil water potential results in a decline of leaf water potential, stomatal conductance, leaf photosynthesis and stem diameter growth while leaf litterfall and leaf flushing increase. (2) During episodic drought, we observe a further decline of stomatal conductance, photosynthesis, stem growth and, in contrast to seasonal drought, also a decline of transpiration. Responses of ecosystem scale processes, productivity and evapotranspiration, are of a smaller magnitude and often not significant. Furthermore, we find that the magnitude and direction of a drought-induced change in photosynthesis, stomatal conductance and transpiration reported in a study is correlated to study-averaged wood density. Therefore, wood density is a good proxy of hydraulic behaviour and can be used to predict leaf and tree scale responses to drought. We present new insights into the functioning of tropical forest in response to drought and offer a response-benchmark for land surface models.

Thomas Janssen et al.
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Short summary
The frequency and severity of droughts is expected to increase in the tropics, impacting the functioning of tropical forests. Here, we synthesized observed responses to drought in neotropical forests. We find that during drought, trees generally close their leaf stomata resulting in reductions of photosynthesis, growth and transpiration. However, on the ecosystem scale, these responses are not visible. This indicates that resistance to drought increases from the leaf to ecosystem scale.
The frequency and severity of droughts is expected to increase in the tropics, impacting the...
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