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Project title : 
Forest trees and changing climate: understanding the past and predicting the future through the analysis of tree ring data
Period : 
April 2008 - August 2011
Coordination : 

It is today crucial to get a clear understanding of the impacts of climate change (long-term trends, isolated events, repetition of extreme phenomena) on forest productivity, since there are major connected economic and environmental issues. This project aims to understand forest decline due to climate change by using the characteristics of tree rings (size and isotopic composition). They will be collected in the forest of Fontainebleau from three major European forest tree species (oak, beech and pine), so as to cover the last 30 years. The links between the characteristics of tree rings and the climate will be examined using both dendrochronological and functional approaches. The study should lead to an improvement of models that simulate the growth of trees on the basis of various climate scenarios, and to improved paleoclimatic reconstructions. 

Labs involved
Non-consortium members : 

EEF: Ecologie et Ecophysiologie Forestières, Nancy
IDES: Interactions et Dynamique des Environnements de Surface, Orsay

Project description


The National Forest Health Monitoring Network has reported a serious decline in forest health for several years now. The observed decline (increased mortality and decreased leaf area index) is attributed to climatic variations and extreme events potentially causing a progressive decrease in forest growth. The impact of climate change on forest productivity is still not properly assessed, despite the fact that the economic and environmental consequences are considerable. It is therefore crucial to improve the understanding and prediction of climate change impact on the growth of different forest tree species, particularly through an improvement of functional models. 


The AFOCLIM project aims to study forest decline due to climate change (droughts in particular) using tree ring data. It will be based on the combination of two approaches whose common characteristic is the use of tree ring isotope data (13C and 18O):

• The dendrochronological/isotopic (dendro-isotopic) approach perfected by LSCE, which consists of studying past interannual variations and their correlation with meteorological variables to develop paleoclimatic reconstruction methods.
• The ecophysiological approach implemented by ESE, which consists of studying inter and intra-annual variations in tree ring isotope composition and interpreting this data in terms of tree carbon and water balance. This approach provides better understanding and better models of carbon balance processes in trees.

The dendrochronological, isotopic, meteorological and hydrological data collected by the different laboratories involved will be compared in order to:

• establish statistical relationships for predicting past climate change impact based on a set of tree ring data,
• simulate seasonal and interannual variations in tree ring growth and isotope composition using a validated ecophysiological model based on the same data set,
• apply this model to analyse the functional response of trees to climate change in terms of growth and water use efficiency,
• propose more or less simplified models to predict past climate conditions based on tree ring data, and future growth based on climatic and silvicultural scenarios. 


Part 1: Acquisition of tree ring data

The following activities will be conducted in the forest of Fontainebleau, chosen as the reference site due to the availability of a significant amount of forest-related documentation (compartments, meteorology, hydrology, exploitation):

• tree ring sampling from three different forest species largely represented in Europe: oak, beech and pine;
• acquisition of beech and pine tree-ring width and isotope data (13C and 18O) covering the past 30 years (oak tree-ring data already acquired). Reliable, homogenised meteorological data is available for this 30 year period.

Fontainebleau forest


Part 2: Analysis of tree ring and climate data

The interannual dendrochronological and isotopic data will be compared with the climate data using correlational approaches based on suitable statistical theories. The soil water content (i.e. water availability for trees) derived from compartment water balance calculations will be taken into consideration in the statistical studies. The responses of the three tree species will be compared. The empirical statistical relationships obtained in this manner will be introduced into a carbon and water balance model developed for continental and global scales (ORCHIDEE).

Tree ring width growth of three main forest species in the forest of Fontainebleau from 1960 to 2007. Convergences and divergences in tree growth as a function of climate can be observed. Certain drought years such as 1976 or 1996 are highly unfavourable to the growth of all three species, whereas others such as 1982 do not affect their growth in the same manner.


Part 3: Functional assessment of relationships between tree ring and climate data

The functional interpretation of tree ring isotope data sets will be based on current knowledge, particularly in terms of water use efficiency for 13C. To date, all tree carbon and water balance processes have been summarised in the CASTANEA forest carbon and water balance model. 13C flux and discrimination parameters were recently introduced into this model. This phase of the project aims to improve the model thus obtained and to add 18O flux data so as to develop a model (ISOCASTANEA) capable of simulating tree growth and both isotope data sets according to a time step. This model could be validated for pluriannual variations using the tree ring data set.

Part 4: Predictions for the future

The ISOCASTANEA and ORCHIDEE models will be used and compared to simulate the long-term impact of extreme climate events on the different tree species based on climate scenarios. A set of simulations varying the intensity and frequency of extreme events will be conducted to examine the impact on tree growth. The potential existence of critical thresholds for survival of these tree species will be studied.

Additional documents and links : 

Research projects related to the AFOCLIM project or devoted to a similar theme

• ACI 'young researchers' project no. 10009 (2004-2007): "Role of ligneous compartments in tree carbon and hydrogen balance processes: Physiological mechanisms and impact at the ecosystem level". Coordination: Claire Damesin (ESE)..

• PNBC project (National ACI-FNS program, Functioning and dynamics of the continental biosphere: Process analysis and modelling) (2004-2007): "Integration of tree and soil functioning for analysis of forest isotope data: A multi-site approach". Coordination: Claire Damesin (ESE).

• ANR CATS project (2007-2010): "Integrated monitoring of carbon allocation in tree and soil". Coordinator: Daniel Epron, University of Nancy, ESE supervisor: Claire Damesin.

These three projects will contribute to the improvement of knowledge on tree rings and 13C isotope composition, and to the development of the functional isotopic forest carbon balance model (ISOCASTANEA) to be used in the consortium project.

• ACI 'young researchers' project no. 10009 (2004-2007): "Role of ligneous compartments in tree carbon and hydrogen balance processes: Physiological mechanisms and impact at the ecosystem level". Coordination: Claire Damesin (ESE).

MAIF ECLID project (2007-2010): "Extreme climate events and dendrochronology". This project aims to analyse and predict the impact of droughts on tree growth and soil water reserves. It is based on the study of a dendrochronological database plotting the evolution of primary tree productivity in Europe during the 20th century.
This project should supplement the AFOCLIM project by establishing correlations between tree-ring width growth and climate data (not including isotope data).

CACIS project, within the framework of the ECLIPSE program (2005-2007): "Tree rings, climate and stable isotopes". This project aims to assess the potential of the dendro-isotopic method for reconstructing climate change by testing tree species still seldom considered, from very different geographical areas. The climatic approach does not work well in this case. Coordination: Valérie Daux (LSCE).

• ACI 'young researchers' project no. 10009 (2004-2007): "Role of ligneous compartments in tree carbon and hydrogen balance processes: Physiological mechanisms and impact at the ecosystem level". Coordination: Claire Damesin (ESE).

• ANR Blanche project (2007-2008): "Modelling the stable isotopes in trees". This project aims to develop a mechanistic model for interpreting the isotope values of the Pinus pinaster species. Coordination: Jérôme Ogée (INRA Bordeaux).

• ANR DRYADE project: "Vulnerability of forests to climate change: Tree growth and bioclimatic factors". Like the AFOCLIM project, this project addresses the vulnerability of temperate forests. It compares the growth of declining and healthy trees so as to assess the determinism of current dysfunctions. It takes into consideration the effects of climate change and extreme events, as well as biotic constraints (diseases) and genetic factors. Coordination: Nathalie Bréda (EEF, INRA Nancy).

Reports and publications

•  Description of the CASTANEA model: Modelling carbon and water cycles in a beech forest, Part I: Model description and uncertainty analysis on modelled NEE.
Dufrêne et coll., Ecological Modelling; 2005.

•  A bi-proxy reconstruction of Fontainebleau (France) growing season temperature from A.D. 1596 to 2000.
Etien et coll., Climate of the past; 4:1-16; 2008

•  Biochemical composition is not the main factor influencing variability in carbon isotope composition of tree rings.
Eglin et coll., Tree Physiology; 28:1619-1628; 2008

•  Signal strength and climate calibration of a European tree-ring isotope network.
Treydte et coll., Geophysical Research Letters; 34; 2007

Glossary : 

• Isotope dendroclimatology: This relatively new technique consists of assessing the stable isotope composition (carbon, oxygen, hydrogen) of wood samples. Stable isotope ratios in tree rings are highly sensitive indicators of climate conditions. This is due to the direct incidence of hydroclimatic factors on the physiological processes that regulate isotope discrimination, which occurs when basic elements (C, O, H) are integrated into the constituent materials of trees.

• Isotope discrimination: Light and heavy isotopes exhibit different ratios, depending on the compound. Isotope discrimination is the phenomenon that modifies these ratios during the passage from one compound to another (via chemical reaction or physical transfer). These changes are low, but measurable (e.g. in tree wood).

• Functional model: Process-based model, as opposed to empirical models based on observation and experience (statistics). 

Project contact : 


Claire Damesin
Professor and Research Scientist at ESE
claire.damesin @ u-psud.fr

PhD student
Alice Michelot
alice.michelot @ u-psud.fr