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

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,
15 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 droughtinduced change in photosynthesis, stomatal conductance and transpiration reported in a study is correlated to study-averaged
20 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.