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Communication Dans Un Congrès Année : 2009

Impact of climate constrains and individual level variability on tree-tree interactions in mountain mixed-forests

Georges Kunstler
G. Vieilledent
Benoît Courbaud
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Résumé

Mountain forests have complex and multiple pathway dynamics which are difficult to predict because stands are often mixed-age and mixed-species, and encompass a large range of climatic conditions. A key point in these dynamics is the way trees interact locally and how these interactions scale up to the community level. The output of local tree-tree interactions is primary driven by differences in ecological strategies between species. However when differences in species strategies are taken into account, tree-tree interactions remain extremely variable. Abiotic factors such as climatic constraints can change species competitive hierarchy and tree-tree interaction intensity. It has been proposed that increasing climate harshness can lead to a decrease of competition intensity or even a shift to positive interaction (facilitation), modifying the importance of tree-tree interactions as a driver of forest dynamics. In addition, intra-specific variability in tree growth, survival and regeneration is high. Intra-specific variability results from genetic variability, past biotic interaction legacy and small environmental effects not measurable by the ecologist and is usually discarded as noise. It can blur species strategies and competitive hierarchy, making the output of tree-tree interactions less clear than based on species average performances. We are currently developing Hierarchical Bayesian models to improve our understanding of local tree-tree interactions in mountain forests. We focus on climate and intra-specific variability effects on these interactions. We will illustrate our research with two examples. A first example analyses the effect of competition on tree growth with a large scale data base. We specifically quantify change of tree-tree interactions (in intensity and in type) with climate. We found limited evidence of a strong effect of climate on tree-tree interaction intensity (competition's absolute impact). There was however large change of the importance (competition's relative impact) of tree -tree interaction with climate, meaning that tree-tree interactions were less important drivers of forest dynamics in harsh climate. A second example analyses tree competition for light, and illustrates how individual variability can change light interception. Light on forest floor appears more heterogeneous when intra-specific variability in crown size and shape is taken into account. This leads to an increase of the number of patches with high light levels, providing more opportunities for the regeneration of light demanding species.
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hal-02596191 , version 1 (15-05-2020)

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Georges Kunstler, G. Vieilledent, Benoît Courbaud. Impact of climate constrains and individual level variability on tree-tree interactions in mountain mixed-forests. Mixed Forests, Oct 2009, Nancy, France. ⟨hal-02596191⟩

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