Raphael Aussenac, Yves Bergeron, Dominique Gravel and Igor Drobyshev
There is mounting evidence that tree species diversity increases the temporal stability of forest growth. This stabilising effect of diversity has mainly been attributed to species differences in their response to fluctuations in environmental conditions. In fact, these differences generate some growth asynchrony which enables compensations among species and thereby stabilises forest growth. Interactions among trees could also contribute to the stabilising effect of diversity, in particular, by increasing tree growth and buffering tree response to fluctuations in environmental conditions. However, this has never been directly demonstrated.
In 2014, we removed wood cores from 1047 trees from five one ha sites within both temperate and boreal mixed forests of Eastern Canada. The tree-ring width time series we obtained enabled us to identify the role of interactions among trees in the stabilising effect of diversity on forest growth.
We found that interactions among trees of different species are less detrimental to growth than interactions among trees of the same species. We also found that interactions among trees of different species could buffer tree response to drought. In other words our results indicate that, when species diversity is high in their vicinity, trees grow better and are less sensitive to fluctuations in environmental conditions.
Thus, we demonstrate that interactions among trees play a role in the stabilising effect of diversity on forest growth. In doing so, we bring to light new mechanisms that have never been demonstrated directly as part of the diversity-stability relationship, either theoretically or empirically. Further studies are needed to determine whether our conclusions hold across a range of climates and forest types.