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

Title of this post comes directly from recently published research paper. The international team of specialists has recently provided an overview of forest productivity changes in different forest regions in Europe under climate change, and tried to divide these changes into effects induced by climate change alone, and by climate change and forest disturbances. Read more what they have found!


Scope of the work

There are evidences that forest productivity and forest disturbances (fire, storm, insects) have increased simultaneously, in the 20th century. Some scientists claim that both these trends are partly associated with a changing climate, and they even project that these trends are going to continue due to ongoing climate change. However, the main problem with forest productivity and forest disturbances studies was that many scientists analyzed them completely separately, neglecting that forest productivity and susceptibility to forest disturbances change dynamically over forest development as affected by environmental (climate, site) conditions.

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Forest productivity and forest disturbances are linked. For instance, disturbances directly affect forest productivity, e.g. through a reduced ability of the ecosystem to capture resources (e.g. lowered leaf area), or forest disturbance susceptibility is often coupled to a specific development phase of the forest and, in consequence, productivity determines the time a forest remains in this specific phase of susceptibility.

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Based on above premises, team of scientists from 12 different countries in Europe, provided an overview of forest productivity changes in different
forests in Europe under climate change, and partition these changes into effects induced by climate change alone and by climate change and forest disturbances.

Results

This study clearly showed that models that included forest disturbances in their simulation runs, reduce significantly forest productivity, and sometimes even cancel out productivity gains in response to climate change.

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Interestingly, in fewer cases, forest disturbances also increase productivity. For instance, low severity fire can alleviate resource competition, increase fertilization, and in the consequence increase forest productivity.

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Researchers pointed clearly, that their results cannot simply be extrapolated to other types of forests and forest disturbances. In order to capture the full range of climate change impacts on forests and to plan adaptation measures, scientists noticed that it is necessary to interpret climate change-induced productivity and forest disturbance changes jointly.

Conceptual framework

Scientists used following conceptual framework (see figure below) and explained that “the interaction between climate change, forest productivity and disturbances can take eight pathways (P1–P8 in the following) which we characterize as ‘direct’ if the interaction is established through a clear cause-effect relationship while we use indirect’ if the interaction is mediated through changes in the forest state”. 

Conceptual framework of interactions between climate change, forest productivity and forest disturbances. Solid, black arrows indicate direct effects; dashed arrows in gray indicate indirect effects mediated through effects on the state of the forests. P1–P8 refer to interaction pathways described in the text. Source: Reyer et al. (2017)

According to the above scheme, the influence of climate change on productivity and forest disturbances can take four pathways (P1–P4) just like the interaction between forest productivity and forest disturbances (P5–P8).

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Scientists used seven forest case studies, which are located in North Karelia (Finland), North Wales (United Kingdom), the South-east Veluwe (The Netherlands), Black Forest (Germany), Montafon (Austria), Prades (Spain) and Chamusca (Portugal). In each case study a specific forest model or differing chains of forest models were applied, and 4 model simultions were performed. There was one simultion that modeled baseline climate scenario, another one included effects of climate change on forest productivity, and last two took previously mentioned ones and added effects of forest disturbances.


Source: Reyer et al. 2017. Are forest disturbance amplifying or canceling out climate change-induced productivity changes in European forests? Environ. Res. Lett. 12 (2017) 034027

Photo credit: The effect of forest fire in the loblolly pine stand, in Florida (USA). Author of the photo: Rafal Chudy

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