Réf. Thuiller & al. 2005

Référence bibliographique complète

THUILLER, W., LAVOREL, S., ARAÚJO, M.B., SYKES, M.T., PRENTICE, I.C. 2005. Climate change threats to plant diversity in Europe. Proceedings of the National Academy of Sciences, USA. 102, 8245-8250.

Abstract: Climate change has already triggered species distribution shifts in many parts of the world. Increasing impacts are expected for the future, yet few studies have aimed for a general understanding of the regional basis for species vulnerability. [The authors] projected late 21st century distributions for 1,350 European plants species under seven climate change scenarios. Application of the International Union for Conservation of Nature and Natural Resources Red List criteria to [their] projections shows that many European plant species could become severely threatened. More than half of the species studied could be vulnerable or threatened by 2080. Expected species loss and turnover per pixel proved to be highly variable across scenarios (27–42% and 45–63% respectively, averaged over Europe) and across regions (2.5–86% and 17–86%, averaged over scenarios). Modeled species loss and turnover were found to depend strongly on the degree of change in just two climate variables describing temperature and moisture conditions. Despite the coarse scale of the analysis, species from mountains could be seen to be disproportionably sensitive to climate change (~60% species loss). The boreal region was projected to lose few species, although gaining many others from immigration. The greatest changes are expected in the transition between the Mediterranean and Euro-Siberian regions. [The authors] found that risks of extinction for European plants may be large, even in moderate scenarios of climate change and despite inter-model variability.

Mots-clés
Intergovernmental Panel on Climate Change storylines, Species extinction, Species turnover, Niche-based model

Organismes / Contact

- Centre d’Ecologie Fonctionnelle et Evolutive, Centre National de la Recherche Scientifique-Unité Mixte de Recherche 5175, 1919 Route de Mende, 34293 Montpellier Cedex 5, France
- Climate Change Research Group, Kirstenbosch Research Center, National Botanical Institute, P/Bag x7, Claremont 7735, Cape Town, South Africa
- Macroecology and Conservation Unit, University of Évora, Estrada dos Leo˜ es, 7000-730 Évora, Portugal
- Laboratoire d’Ecologie Alpine, Centre National de la Recherche Scientifique-Uniteé Mixte de Recherche 5553, Université J. Fournier, B.P. 53X, 38041 Grenoble Cedex 9, France
- Biodiversity Research Group, School of Geography and the Environment, Oxford University, Mansfield Road, Oxford OX1 3TB, United Kingdom
- Geobiosphere Science Centre, Department of Physical Geography and Ecosystems Analysis, Lund University, Sölvegatan 12, 223 62 Lund, Sweden
- QUEST, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, United Kingdom
- Correspondence: thuiller@sanbi.org


(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
       

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
           

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
 
Modélisations

Many European species could be threatened by future climate change. Under the assumption of no migration, more than half of the species considered [in this study] become vulnerable or committed to extinction by 2080. The impacts of climate change are, naturally, less under the universal migration because of the possibility for species to move across landscapes. Under the no-migration assumption and the most severe climate change scenario (A1-HadCM3), 22% of the species become critically endangered (>80% range loss), and 2% extinct by 2080. These numbers decrease for the other scenarios and climate models. Under the universal migration assumption, the results are, as expected, less severe. Under A1-HadCM3, 67% of species would be classified as low risk, whereas under B1-HadCM3, 76% of the species would be at low risk. [These] results coincide with the direction of predictions made by Thomas et al. (11), although the magnitude of the risks [projected here] is less (and note that [the present study] project distributions to 2080, whereas Thomas et al. (11) only projected to 2050]. [...]

Rates of species’ loss and turnover show great variation across scenarios. In A1-HadCM3, the mean European temperature increases by up to 4.4 K, leading to a mean species loss of 42% and turnover of 63%. This scenario provides the widest range of variability across Europe for both species loss (2.5–86%) and turnover (22–90%). The percentage of species loss could exceed 80% in some areas, such as northcentral Spain and the Cevennes and Massif Central in France. B1-HadCM3 gives the lowest expected mean percentage of species loss (27%), reflecting the fact that this scenario has the lowest rate of increase in CO2 and temperature by 2080 (mean European temperature increase of 2.7 K). Other scenarios show intermediate mean rates of species loss (~30%) and turnover (~50%). [...]

Regional deviations from the inferred relationship (positive and negative residuals) can be interpreted as indications of particularly high or low species vulnerability, because of ecological and historical characteristics of the flora, and/or specific environmental conditions. An excess of species loss is shown for mountain regions (mid-altitude Alps, midaltitude Pyrenees, central Spain, French Cevennes, Balkans, Carpathians). Severe climatic conditions have occurred in mountains over evolutionary times, promoting highly specialized species with strong adaptation to the limited opportunities for growth and survival (33). The narrow habitat tolerances of the mountain flora, in conjunction with marginal habitats for many species, are likely to promote higher rates of species loss for a similar climate anomaly than in any other part of Europe (34). By contrast, the southern Mediterranean and part of the Pannonian regions have a negative residual for species loss. Both regions are characterized by hot and dry summers and are occupied by species that tolerate strong heat and drought. Under the scenarios used here, these species are likely to continue to be well adapted to future conditions.

[The authors] finally present mean percentages of species loss and turnover by environmental zones with the A1-HadCM3 scenario of maximum change to best illustrate the spatial patterns. The major spatial patterns are similar over all scenarios. The northern Mediterranean (52%), Lusitanian (60%) and Mediterranean mountain (62%) regions are the most sensitive regions; the Boreal (29%), northern Alpine (25%), and Atlantic (31%) regions are consistently less sensitive. Species turnover shows a somewhat different pattern. The Boreal region could, in principle, gain many species from further south, leading to a high species turnover (66%). The Pannonian region could also theoretically gain eastern Mediterranean species and has a calculated turnover of 66%. Thus, these regions stand to lose a substantial part of their plant species diversity, and (in time) to show a major change in floristic composition. Projected species turnover peaks at the transition between the Mediterranean and continental regions with extirpation of Euro-Siberian species and expansion for Mediterranean or Atlantic species. Southern Fennoscandia is also an area of high potential turnover with the loss of boreal species and gain of Euro-Siberian species. [...]

Hypothèses

These results cannot be taken as precise forecasts given the uncertainties in climate change scenarios, the coarse spatial resolution of the analysis (35), and uncertainties in the modeling techniques used (8, 29). The relatively coarse grid scale of the present study may hide potential refuges for species and environmental heterogeneity that could enhance species survival, especially in mountain areas where the present estimation of risks of extinctions could be overestimated. On the other hand, landscape fragmentation could increase the vulnerability of these refuges to fire or other disturbances, which in combination with the lack of propagule flow, could compromise the survival of remnant populations. There are also major uncertainties due to lags associated with biotic processes. The recognized time scales for assigning species IUCN Red List categories are not suited to evaluating the consequences of slow-acting but persistent threats. [The auithors] have substituted a time scale of 80 years (instead of 20) for critically endangered, endangered and vulnerable, respectively, over which to assess declines. The extent of species losses may be overestimated, because the plasticity of species and the survival of species in favorable microhabitats is not considered. However, even if the numbers are overestimated, patterns across regions may stand (e.g., the ranking of region in terms of vulnerability to loss). Species loss does not necessarily imply the immediate loss of a species from a site, rather it may imply a potential lack of reproductive success and recruitment that will tend to extinction on a longer time scale (36). Migration rates are likely to be species-specific, and resulting biotic interactions in ‘‘no-analogue’’ assemblages may alter species’ realized niches.

Land use and associated habitat fragmentation are likely to generally inhibit migration rates (19). Further, future species distributions will likely be influenced by other environmental factors than changing climate. The current atmospheric CO2 concentration exceeds any experienced during the past 20 million years (12). Plant physiological responses, including growth responses to increased atmospheric CO2 and changes in wateruse efficiency, are expected to ameliorate the response of some plant functional types to climate change (37). On the other hand, nitrogen deposition, the enhanced potential for invasion by exotic species, or the promotion of more competitive native species may change competitive interactions in plant communities, yielding novel patterns of dominance and ecosystem function (38).


Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)

Recent rapid climate change is already affecting a wide variety of organisms (1, 2). Long-term data indicate that the anomalous climate of the past half-century is already affecting the physiology, distribution, and phenology of some species in ways that are consistent with theoretical predictions (3). Although natural climate variation and nonclimatic factors such as land transformation may well be responsible for some of these trends, human-induced climate and atmospheric change are the most parsimonious explanation for many (3, 4). [...]

[The authors] did not assess the impacts of land-use change, even though this factor will potentially compound the effects of climate change on species distributions (25). However, given the spatial extent and resolution of our data and the magnitude of climate change in most projections, the effect of land use would be most likely overridden by climate (26, 27). [...]

Proportion of species classified according to the IUCN Red List assessment:
Niche-based modeling does not address the proximate causes of species extinction. Nevertheless, any reduction in the potential geographic range of a species is likely to lead to an increased risk of local extinction (11). This conclusion is, in fact, the rationale for building IUCN Red Lists (31). A decrease in range size implies that smaller stochastic events affect a larger proportion of the species’ total population, especially in fragmented landscapes. If a species becomes restricted to a few sites, then local catastrophic events (such as droughts or disease outbreaks) or an increase of land transformation by humans could easily cause the extinction of that species (32). [...]

Rates of species’ loss and turnover:
The relationship between the modeled percentage of species loss and the anomalies for the two most significantly correlated bioclimatic variables, growing-degree days (representing accumulated warmth) and a moisture availability index, was used to uncover the potential causes of variations in predicted changes in plant diversity across regions within and across scenarios. The strong consistent linear relationship across scenarios indicates that projected species loss from the models could be estimated from these two predictors. The Spearman rank-correlation values for the separate univariate relationships were 0.73 and 0.65, respectively. Multiple-linear regression by using these two predictors explains 60% of the variance across scenarios. The temperature of the coldest month, although being an important predictor of distributions for many species (6), did not show a strong relationship with species loss overall and was therefore not used in this analysis.

Several studies have modeled future species distributions at regional (5–8) and local scales (9, 10) and have extrapolated alarming extinction risks for the next century (11). However, few studies have considered the consequences of multiple climate-change scenarios (7, 8), which represent the outcome of different assumptions about the future (12). Using four representative scenarios and three different climate models (HadCM3, CGCM2, and CSIRO2), and a range of niche-based modeling techniques implemented in BIOMOD (13), [the authors] develop predictions of the potential consequences for 1,350 plant species in Europe. The ‘‘future climate’’ [they] contrast with today’s climate (averaged from 1961 to 1990) is the projected mean for the period from 2051 to 2080.

The ‘‘bioclimatic envelope’’ describes the conditions under which populations of a species persist in the presence of other biota as well as climatic constraints (6, 14). Future distributions are projected on the assumption that current envelopes reflect species’ environmental preferences, which will be retained under climate change. This principle has strong support from studies demonstrating the evolutionary conservatism of ecological niches and the phylogenetic inertia of species across time scales (15, 16) and comparative biogeographical studies (17, 18). However, this approach also assumes instantaneous species range change, it ignores physiological CO2 responses, and it does not capture details of population dynamics or biotic interactions nor the lags in spatial range shifts associated with processes of dispersal, establishment, and local extinction. To assess the sensitivity of projections to the most critical of these assumptions, [the authors] considered two contrasting assumptions about migration ability (7, 8, 11): either species are unable to disperse at all on the time scale considered (no migration), or they have no constraints to dispersal and establishment (universal migration). The reality for most species is likely to fall between these extremes, depending on their ability to migrate across fragmented landscapes (19). [The authors] calculated losses of climatically suitable areas (‘‘species loss’’) assuming no migration and gains (‘‘species gain’’) and turnover (‘‘species turnover’’) assuming universal migration.

Data Sources:
Species’ distribution data are available for 2,294 plants (20), comprising ~20% of the total European flora, sampled between 1972 and 1996. Modeling was conducted by using available data for Europe on a 50 x 50 km grid. The mapped area comprises western, northern and southern Europe, but excludes most of the eastern European countries where recording effort was both less uniform and less intensive (21). After removing species with <20 records, [the authors] considered range responses of 1,350 plant species of Europe. [They] assume this sample can be taken as representative of the responses of European plant species to climate change because it includes most of the life forms and phytogeographic patterns found among plant species in Europe. Climate data were obtained from the Climatic Research Unit (www.cru.uea.ac.uk) and included mean annual, winter, and summer precipitation, mean annual temperature and minimum temperature of the coldest month (MTC), growing degree days (>5°) and an index of moisture availability (22). These variables were chosen because of their strong link with the physiology and growth of plant species (23, 24). [...] Climate data were averaged for the 1961–1990 period. [...] Future projections were derived by using climate model outputs made available through the Intergovernmental Panel on Climate Change (IPCC) Data Distribution Centre (ipcc-ddc.cru.uea.ac.uk). The modeled climate anomalies were scaled based on four scenarios proposed by the IPCC (12). [see detail in the study...]

Niche-Based Models of Species Climatic Envelops:
[The authors] used the BIOMOD framework, which capitalizes on several widely used niche-based modeling techniques (generalized linear models, generalized additive models, classification tree analysis, and artificial neural networks) to provide alternative spatial projections (13). For each climate change scenario, models relating species distributions to the seven bioclimatic variables were fitted by using BIOMOD and projected into the future. Then, a consensus principal component analysis was run to explore central tendencies in projections and select the niche-based model representing the greatest commonality among projections (8). [...]
To evaluate species extinction risks, the number of pixels lost, potentially gained (under universal migration), or stable by each species [were summed] for the different climate-change scenarios. Each species [was assigned] to an International Union for Conservation of Nature and Natural Resources (IUCN) threat category (IUCN 2001). Those that were not listed were classified as lower risk, depending on the projected reduction in range size from present to 2080. Present and future range sizes (area of occupancy) were estimated from the number of pixels where species occurred. Loss in range size was calculated by subtracting future potential range size from present potential range size. In line with IUCN Red List criterion A3(c), the following thresholds were then used to assign a species to a threat category (IUCN 2001). Extinct is a species with a projected range loss of 100% in 50 or 80 years, critically endangered has a projected range loss of >80%, endangered has a projected range loss of >50%, and vulnerable has a projected range loss of >30%. Although this Red Listing approach is simplistic and considers only the effects of climate change, it provides a synthetic overview of species-specific threats due to climate change.
To evaluate the percentage of extinctions for a given area, the number of species lost (L) by pixel were summed and was related to current species richness by pixel. The procedure was the same to assess the percentage of species gained (G) by pixel (under assumptions that species could reach a new suitable climate space). Percentage of species turnover by pixel, under the assumption of universal migration, is then given by T = 100 x (L + G) / (SR + G) where SR is the current species richness.


(3) - Effets du changement climatique sur l'aléa
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

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

Despite uncertainties, [the present] findings provide illustration of the potential importance and the likely direction of climate change effects. From a conservation perspective, a proportion of European plant species could become vulnerable. The strong positive relationship between projected species loss and changes in bioclimatic variables implies that action to reduce greenhouse gas emissions would also mitigate climate-change effects on plant diversity. However, even under the least severe scenario considered, the risks to biodiversity appear to be considerable. Different regions are expected to respond differently to climate change, with the greatest vulnerability in mountain regions and the least in the southern Mediterranean and Pannonian regions. Recent observations (39) and predictions (9) corroborate [the present] conclusion regarding the climatic sensitivity of species in European mountain areas. [The authors] have also identified a broad transition zone where the greatest species mixing is likely to occur. During the Quaternary period, this region acted both as a crossing point and a refuge zone for Boreo-alpine and Euro-Siberian species (40). This transition zone will be a strategic region for plantspecies conservation in a changing climate.

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