Réf. Lenoir & al. 2008 - A

Référence bibliographique complète
LENOIR J., GEGOUT J. C., MARQUET P. A., DE RUFFRAY P., BRISSE H. A Significant Upward Shift in Plant Species Optimum Elevation During the 20th Century. Science, 2008, Vol. 320, p. 1768-1771.

Abstract: Spatial fingerprints of climate change on biotic communities are usually associated with changes in the distribution of species at their latitudinal or altitudinal extremes. By comparing the altitudinal distribution of 171 forest plant species between 1905 and 1985 and 1986 and 2005 along the entire elevation range (0 to 2600 meters above sea level) in west Europe, the authors show that climate warming has resulted in a significant upward shift in species optimum elevation averaging 29 meters per decade. The shift is larger for species restricted to mountain habitats and for grassy species, which are characterized by faster population turnover. The study shows that climate change affects the spatial core of the distributional range of plant species, in addition to their distributional margins, as previously reported.

Forest plant species, altitudinal distribution, 20th Century evolution, climate change, French mountains.

Organismes / Contact
AgroParisTech, UMR 1092, Laboratoire d'Etude des Ressources Forêt-Bois (LERFoB), 14 rue Girardet, F-54000 Nancy, France. jonathan.lenoir@agroparistech.fr
Center for Advanced Studies in Ecology and Biodiversity (CASEB), Departamento de Ecologia, Pontificia Universidad Católica de Chile, Alameda 340 C.P. 6513677, Santiago, Chile.
Institute of Ecology and Biodiversity (IEB), Casilla 653, Santiago, Chile.
Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA.
CNRS, Institut de Biologie Moléculaire des Plantes (IBMP), Université Louis Pasteur, 12 Rue du Général Zimmer, F-67084 Strasbourg Cedex, France.
CNRS, UMR 6116, Institut Méditerranéen d'Ecologie et de Paléoécologie (IMEP), Faculté des Sciences de Saint Jérôme, case 461, F-34397 Marseille Cedex 20, France.

(1) - Paramètre(s) atmosphérique(s) modifié(s)
(2) - Elément(s) du milieu impacté(s)
(3) - Type(s) d'aléa impacté(s)
(3) - Sous-type(s) d'aléa
Temperature, Precipitation Vegetation    

Pays / Zone
Massif / Secteur
Site(s) d'étude
Période(s) d'observation
France Western Alps, Northern Pyrenees, Massif Central, Western Jura, Vosges and Corsican range     0-2600 m a.s.l. 1905-2005

(1) - Modifications des paramètres atmosphériques
Climatic change in France has been characterized by increases in average temperature of far greater magnitude than increases in the world mean annual temperature, of about 0.6°C over the 20th century (20), reaching up to 0.9°C (21) and even close to 1°C in the alpine region since the early 1980s (22). In contrast, analysis of annual precipitation anomalies between 1965 and 2005 does not show any trend or precipitation regime shift.

Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Annual precipitation anomalies averaged for 73 elevation sites in the French mountains ranging in altitude from 10 to 2010 m a.s.l. (Météo-France data).

(2) - Effets du changement climatique sur le milieu naturel
The optimum elevation of forest plant species shifted mostly upward during the end of the 20 th century. The general upward trend between 1971 (mean year of surveys occurring from 1905 to 1985) and 1993 (mean year of surveys occurring from 1986 to 2005) is statistically highly significant, with a mean difference in optimum elevation of 64.8 m, amounting to an average of 29.4 m per decade.

Interestingly, the size of the species altitudinal range around the optimum elevation did not show a significant change between periods. The observed change in optimum elevation and lack of it in amplitude or range suggest that both the upper and the lower distributional margins may have shifted upward, implying the displacement of the whole altitudinal range. Most species in the 19862005 period had higher optimum elevations than those in the 19051985 period. More than two-thirds (118/171) of the species shifted their optima upward, whereas only one-third (53/171) shifted their optima downward. This overall upward trend is consistent with results focusing on the highest alpine and nival vegetation belts (1012, 28). Forest plant species have already followed the pace of climate change by shifting their distributions to higher altitudes and these changes affect the core of their ranges or those areas where habitat suitability or maximum probability of presence is the highest. Thus, climate warming does not only affect species at their range boundaries, but its consequences ripple through the whole range of species.

Overall, species that shifted the most are mountainous species as compared with ubiquitous species. Similarly, most shifting species tend to have life forms (herbs, ferns, and mosses) involving faster life history traits (shorter life cycle, faster maturation, and smaller sizes at maturity) than do species showing a reduced shift (trees and shrubs). Larger distributional shifts for faster life cycle species are consistent with results already observed in vertebrate taxa (8). Similarly, larger shifts for mountainous species are in agreement with the suggestion that plant species would be more sensitive to climate change at high-altitude locations (10, 11, 17). There is no significant interaction between geographic distribution pattern and life form, which rules out the possibility that forest plant species restricted to mountains show larger changes because most of them exhibit a grassy life form.

Decadal-scale variation in precipitation has remained the same before and after the slicing of our studied period; thus, it cannot directly affect the distributional changes we observed. Atmospheric nitrogen (N) depositions are important at high elevations in western European mountains (33). However, the authors found a slightly lesser but not significant N demand (23) for upward-shifting species as compared with those shifting downward; hence, N deposition did not explain the general upward shift. The effect of land-use changes can also be ruled out because a particular attention was paid to restricting the analysis to mature forests (23), where land-use changes are of reduced magnitude. Lastly, neither invasive species introduction nor changing concentration of atmospheric CO2 seem to be important in determining the observed regional pattern of positive shifts in altitudinal distributions; if present, no significant trend in altitudinal shift would be expected because these drivers are non directional regarding species responses and would affect as many increases as decreases.

The average magnitude of change in forest plant species optimum elevation across the entire altitudinal gradient [29.4 ± 10.9 m per decade (23)] closely matches the figure observed for the shift of alpine plants above the tree line [27.8 ± 14.6 m per decade (12)] and even improves the precision. Further, if we assume a temperature lapse rate of 0.6°C, the results imply a 0.39°C increase in 22 years, which is coherent with the observed warming trend, supporting the hypothesis that climate warming is the main driving force for the observed patterns.

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Temperature increase leads to an upward shift in optimum elevation of forest plant species.
Assuming niche conservatism over evolutionary time (15), the authors tested for large-scale, long-term, and multispecies climate-related responses in forest plant altitudinal distributions. They analyzed species responses by measuring shifts in the altitudinal position of species' maximum probability of presence within their distribution, instead of focusing on distributional extremes. Additionally, they tested for the effect of ecological and life history traits on the magnitude of the response to climate warming (16). In particular, they tested whether species restricted to mountain areas (1012, 17, 18) and/or fast generation times (19) are particularly sensitive to temperature changes. They studied species in forest communities found between lowland to the upper subalpine vegetation belt (0 to 2600 m a.s.l.) over six mountain ranges in west Europe (the Western Alps, the Northern Pyrenees, the Massif Central, the Western Jura, the Vosges, and the Corsican range).

From two large-scale floristic inventories (about 28,000 surveys) (23), the authors extracted two well-balanced subsamples, including 3991 surveys each, carried out across the studied mountain ranges. The first subsample included surveys carried out before the mid-1980s (19051985), and the other one, after 1985 (19862005). The study was restricted to forest communities, where long-term changes outweigh short-term tendencies. By using simple logistic regression, they computed the altitude of maximum probability of presence, also called optimum elevation, within each period for 171 species that were best described by unimodal bell-shaped models (23) and had more than 50 occurrences (25). In total, the studied species account for almost 62% of occurrences in the data set. The change in the altitudinal distribution of species was measured as the difference in their optimum elevation between 19051985 and 19862005.

(3) - Effets du changement climatique sur l'aléa

Paramètre de l'aléa
Sensibilité des paramètres de l'aléa à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)

(4) - Remarques générales

(5) - Syntèses et préconisations

Références citées :

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11. G. Grabherr, M. Gottfried, H. Pauli, Nature 369, 448 (1994).

12. G. R. Walther, S. Beibner, C. A. Burga, J. Veg. Sci. 16, 541 (2005).

15. A. T. Peterson, J. Soberon, V. Sanchez-Cordero, Science 285, 1265 (1999).

16. S. Lavergne, J. Molina, M. Debussche, Glob. Change Biol. 12, 1466 (2006).

17. H. Pauli, M. Gottfried, K. Reiter, C. Klettner, G. Grabherr, Glob. Change Biol. 13, 147 (2007).

18. W. Thuiller, S. Lavorel, M. B. Araujo, M. T. Sykes, I. C. Prentice, Proc. Natl. Acad. Sci. U.S.A. 102, 8245 (2005).

19. M. Cardillo et al., Science 309, 1239 (2005).

20. P. D. Jones, T. J. Osborn, K. R. Briffa, Science 292, 662 (2001).

21. J. M. Moisselin, M. Schneider, C. Canellas, O. Mestre, Meteorologie 38, 45 (2002).

22. M. Beniston, H. F. Diaz, R. S. Bradley, Clim. Change 36, 233 (1997).

23. Materials and methods are available as supporting material on Science Online.

25. C. Coudun, J.-C. Gégout, Ecol. Modell. 199, 164 (2006).

28. P. Lesica, B. McCune, J. Veg. Sci. 15, 679 (2004).

33. E. Dambrine et al., in Forest Decline and Atmospheric Deposition Effects in the French Mountains, G. Landmann, M. Bonneau, Eds. (Springer Verlag, Berlin, 1994), pp. 177200.