Are forest disturbances amplifying or canceling out climate change-induced productivity changes in European forests?

Abstract

Recent studies projecting future climate change impacts on forests mainly consider either the effects of climate change on productivity or on disturbances. However, productivity and disturbances are intrinsically linked because 1) disturbances directly affect forest productivity (e.g. via a reduction in leaf area, growing stock or resource-use efficiency), and 2) disturbance susceptibility is often coupled to a certain development phase of the forest with productivity determining the time a forest is in this specific phase of susceptibility. The objective of this paper is to provide an overview of forest productivity changes in different forest regions in Europe under climate change, and partition these changes into effects induced by climate change alone and by climate change and disturbances. We present projections of climate change impacts on forest productivity from state-of-the-art forest models that dynamically simulate forest productivity and the effects of the main European disturbance agents (fire, storm, insects), driven by the same climate scenario in seven forest case studies along a large climatic gradient throughout Europe. Our study shows that, in most cases, including disturbances in the simulations exaggerate ongoing productivity declines or cancel out productivity gains in response to climate change. In fewer cases, disturbances also increase productivity or buffer climate-change induced productivity losses, e.g. because low severity fires can alleviate resource competition and increase fertilization. Even though our results cannot simply be extrapolated to other types of forests and disturbances, we argue that it is necessary to interpret climate change-induced productivity and disturbance changes jointly to capture the full range of climate change impacts on forests and to plan adaptation measures.

This study was initiated as part of the MOTIVE project funded by the Seventh Framework Program of the EC (Grant Agreement No. 226544) and benefitted further from the discussion carried out in the COST Action FP1304 PROFOUND as well as the Module E.8 of the IUFRO Task Force on 'Climate Change and Forest Health'. CPOR acknowledges funding from the German Federal Ministry of Education and Research (BMBF, grant no. 01LS1201A1). MJS and KK acknowledge funding from the strategic research programme KBIV 'Sustainable spatial development of ecosystems, landscapes, seas and regions', funded by the Dutch Ministry of Economic Affairs. KK was additionally funded by the Knowledge Base project Resilient Forests (KB-29-009-003). RS acknowledges further support from the Austrian Science Fund FWF through START grant Y895-B25. HP acknowledges funding from the strategic research council of Academy of Finland for FORBIO project (no. 14970). The ISA-authors acknowledge funding from the CEF research Centre by project UID/AGR/00239/2013. NEZ acknowledges further support from Rafael O Wüest and from the Swiss Science Foundation SNF (grant #40FA40_158395). CTFC authors acknowledge funding from MINECO (Ref. RYC-2011-08983, RYC-2013-14262, AGL2015-67293-R MINECO/FEDER) and from CERCA Programme / Generalitat de Catalunya.