Influence of vegetation spatial structure on growth and water fluxes of a mixed forest: Results from the NOTG 3D model

Abstract

Many natural terrestrial ecosystems, agroforestry systems, and, increasingly, forest plantations, are made of a mixture of species and display significant structural heterogeneity. Yet most carbon-based biophysical models are limited to homogeneous, monospecific canopies.We explored whether the spatial structure at the Font-Blanche experimental site, located in a mixed Mediterranean forest of Aleppo pine and holm oak in south-east France, could affect the components of the carbon and water cycles. We used NOTG, a new 3D, process-based, and individual-based model specifically developed to study the importance of the spatial structure on the carbon and water cycles of complex ecosystems. It incorporates processes involved in the energy, carbon, and water cycles at the tree (radiation interception, photosynthesis, phenology, allocation, senescence, transpiration), and soil (soil moisture, soil organic matter decomposition) levels. It is designed to handle various plant phenological types (deciduous, non opportunistic evergreen, and opportunistic evergreen), and a comprehensive description of plant C pools. The model is designed to study water and carbon fluxes at the stand scale over one to a few years.In this study, NOTG was parameterized for the Font-Blanche forest and two five-year simulations were made using either the full 3D representation, or a simplified 1D representation. Comparison of model outputs against observations at the tree, soil, and ecosystem scales, showed a much better accuracy when using the 3D representation. This illustrates the dependence of plant and ecosystem function to the above- and below-ground spatial structures, and the usefulness of such detailed models when dealing with structurally complex ecosystems.