Abstract
Abstract. Given the multiple abiotic and biotic stressors resulting from global changes, management systems and practices must be adapted in order to maintain and reinforce the resilience of forests. Among others, the transformation of monocultures into uneven-aged and mixed stands is an avenue to improve forest resilience. To explore the forest response to these new silvicultural practices under a changing environment, one needs models combining a process-based approach with a detailed spatial representation, which is quite rare. We therefore decided to develop our own model (HETEROFOR for HETEROgeneous FORest) according to a spatially explicit approach, describing individual tree growth based on resource sharing (light, water and nutrients). HETEROFOR was progressively elaborated within Capsis (Computer-Aided Projection for Strategies in Silviculture), a collaborative modelling platform devoted to tree growth and stand dynamics. This paper describes the carbon-related processes of HETEROFOR (photosynthesis, respiration, carbon allocation and tree dimensional growth) and evaluates the model performances for three broadleaved stands with different species compositions (Wallonia, Belgium). This first evaluation showed that HETEROFOR predicts well individual radial growth (Pearson's correlation of 0.83 and 0.63 for the European beech and sessile oak, respectively) and is able to reproduce size–growth relationships. We also noticed that the net to gross primary production (npp to gpp) ratio option for describing maintenance respiration provides better results than the temperature-dependent routine, while the process-based (Farquhar model) and empirical (radiation use efficiency) approaches perform similarly for photosynthesis. To illustrate how the model can be used to predict climate change impacts on forest ecosystems, we simulated the growth dynamics of the mixed stand driven by three IPCC climate scenarios. According to these simulations, the tree growth trends will be governed by the CO2 fertilization effect, with the increase in vegetation period length and the increase in water stress also playing a role but offsetting each other.
Highlights
Forest structure and composition result from soil and climate conditions, management, and natural disturbances
HETEROFOR was run with different combinations of options for describing photosynthesis, respiration and crown extension
The predictions carried out using the photosynthesis routine of CASTANEA were generally slightly better correlated to the observations than those obtained with the PAR use efficiency (PUE) approach, which displayed somewhat lower RMSE (Table 3)
Summary
Forest structure and composition result from soil and climate conditions, management, and natural disturbances. As the combinations of site conditions, climate projections, stand structures and tree species compositions are nearly infinite, all of the management options that could potentially enhance the resilience and adaptive capacity of forests cannot be tested in situ (Cantarello et al, 2017). Such silvicultural trials provide results only for the long run, given the life span of trees, and cannot anticipate future conditions. To explore the forest response to new silvicultural practices and yet unexperienced climate conditions in a realistic way, one needs new process-based models that are able to deal with mixed and structurally complex stands and to incorporate uncertainties in future conditions (Berger et al, 2008; Bravo et al, 2019)
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