The response of individuals to their environment is determined by a set of life traits, which are usually assumed as characteristic of species in modelling and experimental studies. Genetic variability, local micro-variations and historical contingency lead nevertheless to variations of traits among individuals of a same species. This intra-specific variability has been shown to influence the establishment of size hierarchies within plant populations. In some cases, it also blurs species differences and can influence species coexistence. The objective of this work was to evaluate whether intra-specific variability has a significant impact on the development of spatial and temporal structures in pure and mixed forests. We quantified intra-specific variability of growth within populations of Norway spruce and European Fir in the Alps, using a Hierarchical Bayesian approach. We then simulated the development of spruce-fir forests in a spatially explicit, individual-based model and compared patterns obtained with and without intra-specific variability.

Results/Conclusions

Taking intra-specific-variability into account increased height differentiation, spatial aggregation and stand annual productivity. It decreased the maximum basal area reached during stand development, leading to a better agreement to field observation.  It also eliminated oscillations of basal area in mature forests, an artificial pattern often observed in forest models. In our simulations, intra-specific variability had little influence on the dynamics of succession. Fir eliminated spruce on the long term. Nevertheless, this pattern could depend on environmental conditions. Intra-specific variability appeared in this study as an important factor improving both community dynamic pattern understanding and quantitative predictions.