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How to better understand the processes behind the climate’s influence

Xavier Morin (CNRS) takes the floor

How to better understand the processes behind the climate’s influence on trees in order to anticipate the effects of climate change on forest composition and forest ecosystem functions

Summary

Climate change affects the environment at all ecological scales, from individuals to populations and from species and ecosystems to whole biomes (Valladares, 2008). Climatic conditions also profoundly influence the ecological niche occupied by forest tree species by closely affecting tree physiological processes. Indeed, the impact of climate change on tree species is already visible: changes have been observed in individual tree physiology (Saxe et al., 2001), in particular related to phenology (Lebourgois et al., 2008; Morin et al., 2010), tree species geographical distribution (Lenoir et al., 2008) and community composition (Bertrand et al., 2011). Such modifications in turn alter global biodiversity, and functions in the ecosystems stemming from it (Kinzig et al., 2002; Morin et al., 2011).

Faced with such a deluge of impacts, we must improve our understanding of the processes involved to better anticipate the effects of climate change; we must develop our capacity to integrate the complexities of ecosystem functioning into our knowledge and to identify the parameters that best reveal how ecosystems respond to the climate (Morin, 2006). With this goal in mind, long-term observations, such as those carried out by the RENECOFOR network for the past 25 years, become exceedingly important. Indeed, only this type of data makes it possible to reveal the effects of climate on ecological processes such as species phenological responses or individual growth, and to take these effects into account in robust predictive models for the future.

In this presentation, I will give an overview of the current strategies being used to understand these processes and to simulate the impact of climate (and modifications in the climate) on forest trees. I will particularly focus on the effects of climate on tree species distribution and on the relative growth of forest tree species in mono-specific or mixed stands. More precisely, I will attempt to show how long-term monitoring data allows us to answer the following questions:

  • What changes in the distribution ranges of forest tree species can be expected?
  • To what degree can species mixtures improve a forest's adaptability to climate, taking into account the link between species community composition and ecosystem functioning?

The answers to these questions are based on results provided by the PHENOFIT (Chuine & Beaubien, 2001; Cheaib et al., 2012) (as shown in the figure below) and ForCEEPS (Morin et al., in prep) models.

Sample simulation of the distribution range for beech in 2055 produced by the PHENOFIT model. In green: areas where the species is predicted to remain in place; in red: areas where the species is likely to have disappeared by 2055; in blue: areas the species may colonise in 2055
Sample simulation of the distribution range for beech in 2055 produced by the PHENOFIT model. In green: areas where the species is predicted to remain in place; in red: areas where the species is likely to have disappeared by 2055; in blue: areas the species may colonise in 2055 © Xavier Morin / CNRS

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