MAESPA: a model to study interactions between water limitation, environmental drivers and vegetation function at tree and stand levels, with an example application to [CO<sub>2</sub>] × drought interactions

Abstract

Abstract.Process-based models (PBMs) of vegetation function can be used to interpret and integrate experimental results. Water limitation to plant carbon uptake is a highly uncertain process in the context of environmental change, and many experiments have been carried out that study drought limitations to vegetation function at spatial scales from seedlings to entire canopies. What is lacking in the synthesis of these experiments is a quantitative tool incorporating a detailed mechanistic representation of the water balance that can be used to integrate and analyse experimental results at scales of both the whole-plant and the forest canopy. To fill this gap, we developed an individual treebased model (MAESPA), largely based on combining the well-known MAESTRA and SPA ecosystem models. The model includes a hydraulically-based model of stomatal conductance, root water uptake routines, drainage, infiltration, runoff and canopy interception, as well as detailed radiation interception and leaf physiology routines from the MAES-TRA model. The model can be applied both to single plants of arbitrary size and shape, as well as stands of trees. The utility of this model is demonstrated by studying the interaction between elevated [CO 2 ] (eC a ) and drought. Based on theory, this interaction is generally expected to be positive, so that plants growing in eC a should be less susceptible to drought. Experimental results, however, are varied. We apply the model to a previously published experiment on droughted cherry, and show that changes in plant parameters due to long-term growth at eC a (acclimation) may strongly affect the outcome of C a × drought experiments. We discuss potential applications of MAESPA and some of the key uncertainties in process representation.

Modeling stomatal conductance in the earth system: linking leaf water-use efficiency and water transport along the soil–plant–atmosphere continuum

“…A stem conductance k p = 4 mmol H 2 O m −2 s −1 MPa −1 gives a whole-plant conductance k L = 2 mmol H 2 O m −2 s −1 MPa −1 for moist soil with neglibile soil resistance, if root and stem conductances are equal. Duursma and Medlyn (2012) Ollinger et al (2008). c Estimated using empirical relationships between N area and V cmax25 from the TRY leaf trait database (Kattge et al, 2009) with observed foliage N converted from N mass to N area using the mean leaf mass per unit area (LMA) for temperate forest trees reported in the Glopnet leaf trait database (Wright et al, 2004).…”

Sensitivity and uncertainty analysis of the carbon and water fluxes at the tree scale inEucalyptusplantations using a metamodeling approach

“…The MAESPA model (Duursma and Medlyn 2012) coupled the soil water balance components of the SPA model (Williams et al 1996) to the MAESTRA model (Medlyn 2004), with some major changes and additions. MAESTRA was a 3D single-tree and stand process-based model that calculated light interception and distribution within crowns and used a leaf physiology submodel to estimate photosynthesis and transpiration.…”

“…The computational efficiency of 3D PBMs can be improved by representing individual tree crowns as simple shapes such as ellipsoids or cones (e.g., MAESTRA model, Medlyn 2004; MAE-SPA model, Duursma and Medlyn 2012). Such models, however, require a larger set of parameters than stand-scale PBMs, thus limiting their use in forestry.…”

High organic inputs explain shallow and deep SOC storage in a long-term agroforestry system – combining experimental and modeling approaches

“…Several models have been developed to simulate interactions for light, water, and nutrients between trees and crops (Charbonnier et al, 2013;Duursma and Medlyn, 2012;van Noordwijk and Lusiana, 1999;Talbot, 2011) or to predict tree growth and crop yield in agroforestry systems (Graves et al, 2010;. However, none of these models are designed to simulate SOC dynamics in agroforestry systems and they are therefore not useful to estimate SOC storage.…”