The impact of tree species diversity and climate change on forest productivity in central Europe

Background/Question/Methods

Ongoing climate change affects forest functioning processes such as productivity. However, climate change will also alter forest biodiversity through shifts in species distribution and changes in community composition, which in turn modifies forest productivity. Understanding the link between biodiversity and productivity and how it will be affected by climate change are thus two decisive issues in the context of global biodiversity loss.

The relationship between species richness and productivity has been explored widely through experiments, usually showing a positive relationship, but without being able to explain how this effect will unfold in the long-term, especially in forests. Furthermore, the impact of climate change on this relationship has been never explored in forests. We used a novel approach to study (i) the response of forest productivity to changes in tree species richness and (ii) how climate change may affect this response, employing the process-based forest succession model ForClim along an environmental gradient across Switzerland and Germany (11 sites).

Results/Conclusions

First, we show that tree diversity influences productivity in European temperate forests across a wide range of climatically distinct sites through a strong complementarity effect. Hence, our results confirm the positive diversity-productivity relationship found in grassland experiments, and the increasing relative importance of complementarity in comparison with selection through time. Second, we show that increasing tree diversity leads to greater stability of forest productivity, mostly because of a larger asynchrony in species fluctuations when more species are present in the forest. We also show that these results are strongly influenced by functional diversity. Third, we quantify how climate change affects the relationship between diversity and productivity at the study sites by performing simulations using scenarios from three Regional Climate Models. In particular we show that biodiversity will have  a strong positive effect on productivity in sites with harsher conditions in the future. Our study thus provides a new basis to disentangle the role of diversity as a crucial driver for productivity in forests and to make predictions about the impact of climate change on forest ecosystems.