Long-term response of forest productivity to climate change is mostly driven by change in tree species composition

Hervé Jactel,Michael Scherer-Lorenzen,Lorenz Fahse,Raúl García-Valdés,Xavier Morin,Harald Bugmann

doi:10.1038/s41598-018-23763-y

Abstract

Climate change affects ecosystem functioning directly through impacts on plant physiology, resulting in changes of global productivity. However, climate change has also an indirect impact on ecosystems, through changes in the composition and diversity of plant communities. The relative importance of these direct and indirect effects has not been evaluated within a same generic approach yet. Here we took advantage of a novel approach for disentangling these two effects in European temperate forests across a large climatic gradient, through a large simulation-based study using a forest succession model. We first showed that if productivity positively correlates with realized tree species richness under a changed climate, indirect effects appear pivotal to understand the magnitude of climate change impacts on forest productivity. We further detailed how warmer and drier conditions may affect the diversity-productivity relationships (DPRs) of temperate forests in the long term, mostly through effects on species recruitment, ultimately enhancing or preventing complementarity in resource use. Furthermore, losing key species reduced the strength of DPRs more severely in environments that are becoming climatically harsher. By disentangling direct and indirect effects of climate change on ecosystem functioning, these findings explain why high-diversity forests are expected to be more resilient to climate change.

Highlights

Forests are of critical importance globally; they cover ca. 30% of the world’s land surface, harbor most of terrestrial biodiversity[1], are an important carbon sink[2], have a pivotal role for climate regulation[3] and provide many other ecosystem services[4]
While understanding the interaction between climate change and the loss of biological diversity represents a crucial challenge to forecast ecosystem functioning in the future[19,31], the relative importance of the direct and indirect effects of climate change has not been yet evaluated within the same general approach
Our results demonstrate that forest productivity positively correlates with realized tree species richness even under a changed climate, i.e. as it is getting warmer and drier, for a large panel of baseline conditions

Summary

Introduction

Forests are of critical importance globally; they cover ca. 30% of the world’s land surface, harbor most of terrestrial biodiversity[1], are an important carbon sink[2], have a pivotal role for climate regulation[3] and provide many other ecosystem services[4]. While understanding the interaction between climate change and the loss of biological diversity represents a crucial challenge to forecast ecosystem functioning in the future[19,31], the relative importance of the direct (i.e., through species response to abiotic conditions) and indirect (i.e., through changes in community composition) effects of climate change has not been yet evaluated within the same general approach. We used a FSM to quantify the potential relative importance of these direct and indirect effects on forest productivity, and to test how DPRs are theoretically affected by climate change, considering combinations of 30 European tree species and a wide range of environmental conditions in Central Europe (Table S1). Indirect effects should be prevalent in the less productive sites, where tree species diversity is lower and forest functioning more likely to strongly depend on a few key species[29,33]

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