Climate change impacts on long-term forest productivity might be driven by species turnover rather than by changes in tree growth

Abstract

Aim: Climate change impacts forest functioning and services through two inter-related effects. First, it impacts tree growth, with effects, for example, on biomass production. Second, climate change might also reshuffle community composition, with further effects on forest functioning. However, the relative importance of these two effects has rarely been studied. Here, we developed a novel modelling approach to investigate such importance for forest productivity. Location: 11 forest sites in central Europe. Time period: Historical (years 1901-1990) and end-of the-century (2070-2100) climatic conditions. We simulated 2000 years of forest dynamics for each condition. Major taxa studied: 25 common tree species in European temperate forests. Methods: We coupled species distribution models and a forest succession model, working at complementary spatial and temporal scales, to simulate the climatic filtering shaping potential tree species pools, the biotic filtering shaping realized communities, and the functioning of these realized communities in the long term. Results: Under an average temperature increase (relative to 1901-1990) of between 1.5 ºC and 1.7 ºC, changes in simulated forest productivity were mostly caused by changes in the growth of persisting tree species. With an average temperature increase of 3.6 ºC – 4.0 ºC, changes in simulated productivity at currently climatically mild sites were again predominantly caused by changes in tree species growth. However, at the currently warmest and coldest sites, productivity changes were mostly related to shifts in species composition. In general, at the coldest sites, forest productivity is likely to be enhanced by climate change, and at the warmest sites productivity might increase or decrease depending on the future regime of precipitation. Main conclusions: Combining two complementary modelling approaches that address questions at the interface between biogeography, community ecology, and ecosystem functioning, reveals that climate change-driven community reshuffling in the long term might be critically important for ecosystem functioning.