DRESS

There is an emerging agreement on the central role of water in determining the response of terrestrial ecosystems to climate change, based on the high sensitivity of forests to changes in the hydrological regime. Drought-induced shifts in tree and forest function have been identified as major threats. These shifts range from near-instantaneous metabolic and physiological responses of individual leaves to shifts in tree population demography and community sorting. Anticipating climate change effects is especially important at landscape to regional scales, because this range of scales is where forest policy and management actions are implemented. In addition, three temporal scales have to be considered if we are to increase our capacity to forecast forest responses to drought.

Short-term responses (hours to days) revolve around the regulation of stomatal conductance and photosynthesis. Long-term responses (months to years) include plasticity and acclimation in allocation, metabolic and hydraulic traits. Finally, evolutionary processes and constraints shape the co-variation of functional traits across species, and determine the variety of successful life history strategies.

The general aims of this proposal are to (i) develop and test novel physiological theory merging the concepts of instantaneous optimization of gas exchange and longterm acclimation to drought, and (ii) implement this theory into a structured population forest model and apply it to forecast regional forest dynamics under climate change.

We propose to carry out this programme by combining empirical analyses of existing and novel meta-databases (WP1), experimental manipulations to investigate plasticity and acclimation across a wide range of species (WP2), tests of alternative hypotheses of stomatal optimization and water use strategies, based on detailed physiological modelling and empirical data (WP3 and 4), and advanced, regional-scale modelling that accounts for plant trait variability and co-variation to predict the effects of climate on forest functioning and dynamics (WP5).

Four unique elements of novelty are present in this proposal: a) the use of a newly published stomatal and photosynthesis model that offers great promise in simulating plant gas exchange at large spatial scales; b) the use of novel global-scale meta-databases for theory building and model development; c) the use of cutting-edge metabolomics techniques, and d) the implementation of empirical data and theoretical developments in a population-structured forest model to be run at regional scale.

Since we aim at improving our capacity of forecasting where and when changes in forest function and dynamics are likely to occur, we will provide managers and policy-makers with specific knowledge that can inform management and policy to ensure a sustained provision of ecosystem services and maximize the role of forests in climate change mitigation. The key focus on modelling water flows at local to regional scales will also allow an improved assessment of the impacts of different climate and management scenarios on this resource, a particularly relevant issue in a Mediterranean context.

Finally, model predictions of daily variations in leaf relative water content across a whole region will be essential to provide live fuel moisture estimates and develop operational tools helping wildfire risk rating.