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Sounding the alert: forests face the threat of climate change

International experts have issued a joint declaration to raise public awareness about the possible widespread forest tree deaths due to climate change and the resulting social and ecological implications.

Widespread mortality of fir trees (Abies alba) in the Alpes-Maritimes region of France. © INRA, Hendrik Davi
By Pascale Mollier, translated by Teri Jones-Villeneuve
Updated on 12/18/2014
Published on 11/28/2014

Alerting the public

A group of 65 scientists from around the world met in October 2014 at the Max Planck Institute in Jena, Germany, to discuss tree physiology, forest ecology and mathematical modelling. They have issued a declaration on the risks of tree die-off due to climate change.

The scientists aim to raise public awareness about the potential risks and consequences for society related to the widespread tree mortality and show that it is possible to reduce this risk by lowering greenhouse gas emissions.

This declaration is particularly timely as France gets ready to host the Twenty-first session of the Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCCC COP21) in 2015.

Numerous researchers from INRA, Irstea, CNRS and various universities will be dealing with this theme. Hendrik Davi, researcher at INRA’s Avignon centre who heads up a project on forest adaptation to climate change(1) is one such scientist. “There is no doubt that, mechanically speaking, ongoing climate change and more frequent drought periods will affect forests. If temperatures rise an average of 2°C globally as predicted (including oceans), temperatures will most likely be higher in certain regions. “For example, in the Mediterranean area (a focus point of Davi’s research), temperatures could rise as much as 5°C and conditions at an altitude of 1600 m today would be reached at just 900 m. “Widespread tree deaths have been reported for fir, Scots pine and Norway spruce species following the 2003–06 drought period,” says Davi. “We’ve also shown the aggravating role that insects and other pathogens can play, which makes predicting mortality phenomena rather difficult,” he adds.

Continuing research efforts

“The workshop in Germany was an opportunity to bring together and organise members of the scientific community studying tree mortality,” says Davi. “Existing observation networks spread across different countries need to cooperate more closely to better assess the phenomenon and show the link between current climate change, which has not yet been formally established.”

Henrik Hartmann, workshop organiser and director of the Max Planck Institute for Biogeochemical Processes, says, “The scientists at our workshop jointly concluded that such data are not only critical to motivate action from governments, policy makers and forest managers, but also to devise specific action strategies to mitigate the underlying climatic conditions.”

The scientists listed a number of areas to explore, including:

  • Physiological mechanisms involved in tree mortality
  • Shifting the scale, from the tree to the watershed and regional levels, with input from modelling
  • Differential vulnerability of trees to drought and pathogens (leaf size, root/leaf ratio, etc.)
  • Interaction between various disturbances: drought, fire, pathogens, etc.

(1)    FORADAPT project “Assessing potentials of forest adaptation to climate change”, financed through the INRA metaprogramme “Adaptation of agriculture and forests to climate change” (AAFCC).

Scientific contact(s):

Associated Division(s):
Forest, Grassland and Freshwater Ecology
Associated Centre(s):
Provence-Alpes-Côte d'Azur

How a tree dies

Death spiral of a tree. Illustration by Paul D. Manion, 1991.. © P. D. Manion
Death spiral of a tree. Illustration by Paul D. Manion, 1991. © P. D. Manion

Aside from the natural ageing process, a number of factors may cause a tree’s health to progressively decline. Research conducted in the 1970s enabled scientists to classify these factors into three categories: predisposing factors (soil quality, genetics), inciting factors (drought) and contributing factors (pathogens). When these factors are compounded, illustrated as a spiral (Manion’s “decline disease spiral”), the tree may die.

The effects of drought are evident in different ways: moderate, repeated droughts cause stomata to close in order to limit evapotranspiration, which in turn causes decreased CO2 absorption leading to stunted growth. An intense drought can also cause cavitation phenomena (the appearance of air bubbles in vessels and the interruption of sap circulation), which may be serious enough to cause sudden death.


Special issue of the Annals of Forest Science (Volume 71, Issue 7, September 2014).