MAESPA: a model to study interactions between water limitation, environmental drivers and vegetation function at tree and stand levels, with an example application to [COsub2/sub] × drought interactions

摘要

Process-based models (PBMs) of vegetation function can be used to interpretand integrate experimental results. Water limitation to plant carbon uptakeis a highly uncertain process in the context of environmental change, andmany experiments have been carried out that study drought limitations tovegetation function at spatial scales from seedlings to entire canopies.What is lacking in the synthesis of these experiments is a quantitative toolincorporating a detailed mechanistic representation of the water balancethat can be used to integrate and analyse experimental results at scales ofboth the whole-plant and the forest canopy. To fill this gap, we developedan individual tree-based model (MAESPA), largely based on combining thewell-known MAESTRA and SPA ecosystem models. The model includes ahydraulically-based model of stomatal conductance, root water uptakeroutines, drainage, infiltration, runoff and canopy interception, as well asdetailed radiation interception and leaf physiology routines from theMAESTRA model. The model can be applied both to single plants of arbitrarysize and shape, as well as stands of trees. The utility of this model isdemonstrated by studying the interaction between elevated [CO₂](eC_a) and drought. Based on theory, this interaction is generallyexpected to be positive, so that plants growing in eC_a should be lesssusceptible to drought. Experimental results, however, are varied. We applythe model to a previously published experiment on droughted cherry, and showthat changes in plant parameters due to long-term growth at eC_a(acclimation) may strongly affect the outcome of C_a × droughtexperiments. We discuss potential applications of MAESPA and some of the keyuncertainties in process representation.