Linking form to function: Simulating plant hydraulic strategies’ impact on tree drought response in a tropical montane rainforest

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Multidimensional trait relationships are imperative to understanding forest functioning in the face of ongoing environmental changes. Warming and more frequent and severe water stress are expected to adversely affect tropical forests’ large carbon uptake capacity. Therefore, it is, important to evaluate how tropical trees would perform under future climate scenarios. It is challenging to analyse trait-performance relationships solely based on observational data. However, process-based models representing key plant trait trade-offs can be applied to investigate the influence of different plant hydraulic strategies on tropical tree performance.We used a hydraulics-enabled version of the Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS) to study how trait relationships influence tropical plant performance on three study sites included in the RwandaTREE (Rwanda tropical elevation gradient) experiment. We parameterised four endemic species based on observational data and ran simulations by varying selected traits within the potential ranges to evaluate how these parameters affect the simulated biomass and woody growth rate.The results showed a variation in optimum trait values which led to realistic simulated woody growth rates, depending on successional strategies and study sites. This can be attributed to the emerging functional strategies defined by the trait relationships. Our results highlight that we can evaluate complex trait relationships and trade-offs that cannot feasibly be measured across large scales. This allows us to formulate new hypotheses on which hydraulic and structural trait correlations define plant performance. Increased understanding of drought-related vegetation processes can be used to decrease uncertainty in simulating tropical forest resilience and extreme weather impact on Pan-African carbon stocks.

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