Réf. Tinner & Ammann 2005 - A

Référence bibliographique complète

TINNER, W., AMMANN, B. 2005. Long-term responses of mountain ecosystems to environmental changes: resilience, adjustment, and vulnerability. In U.M. Huber et al. (eds), Global Change and Mountain Regions, Springer, 133-143.

 

Mots-clés
Alps, Climate change, Human impact, Fire history, Paleoecology, Vegetation history

Organismes / Contact

Institute of Plant Sciences, Section Paleoecology, University of Bern, Altenbergrain 21, CH-3013 Ber, Switzerland – willy.tinner@ips.unibe.ch


(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
Temperatures (+ precipitations) Vegetation    

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Western Alps See references in the study See references in the study North and South of the Alps... See references... The Holocene...

(1) - Modifications des paramètres atmosphériques
Reconstitutions

According to recent quantitative studies on chironomid assemblages (Heiry 2001), the Holocene climatic optimum in the Alps was reached at around 6500 cal. yr BP (calendar years before present, i.e. 1950 AD), when temperatures were about 1.3-1.5°C warmer than today. These results are supported by alpine timberline studies (e.g. Tinner et al. 1996; Tinner and Theurillat, in press), and it is assumed that overall climatic conditions in the Alps at this time were moderately more continental than today (Tinner and Ammann 2001). [...]

The late-glacial and Holocene records (e.g. Ammann et al. 2000; Tinner and Lotter 2001) suggest that large-scale vegetation changes in the Alps occured when temperature variations exceeded 1.5-2°C. Temperature changes were often accompanied by precipitation variations [...].

Observations

 

Modélisations
 
Hypothèses
 

Informations complémentaires (données utilisées, méthode, scénarios, etc.)
[See references...]

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

The reconstructed vegetation distribution in the Alps at ca. 6500 yr BP is stikingly different from today and challenges some of the ecological "beliefs" that have been derived from present distributions. For example, recent paleoecological studies show that Abies alba (white fir, the tallest tree of Europe at ~70 m height) was able to co-dominate stands situated betwenn 200 m in the southern Alps and 1900 m in the northern Alps under reconstruced July temperatures betwenn ~24° and 10°C, respectively. In contrast, reliance on today's observations implies that the species is competitive only at sites with July means of ~18°-13°C. The paleoecological results suggest that today's constricted geographical range is largely determined by disturbance (especially by fire). [See references given in the study...]

New paleoecological results suggest that many vegetation types in the Alps responded with displacement (vulnerability) or adjustment during the past 6500 cal. yr, whereas only a few showed resilient behaviour on such long time scales. [...]

[See examples given in the study...]

On the basis of [the exemples given in the study], it is difficult to conclusively answer the question wheteher some communities are more vulnerable than others to climatic change and human impact. In the Alps, most disturbance since ca. 6000 cal. yr BP were of human origin, and there are clues that fire was the decicive tool. In this context, it is intriguing that the most vulnerable species was Albies alba. Among all tree species, it had the largest areaa losses in the western Alps during the past 6500 years. The species is very fire-sensitive (Tinner et al; 2000) and subject to intensive browsing during winter. It was also the most highly prized timber for construction (Küster 1994). However, other fire-sensitive taxa (e.g. Tilia, Ulmus, Fraxinus) were also heavily reduced, causing the displacement of entire communities. Conversely, the most resislient communities were situated in the longitudinal inner-Alpine valleys (Pinus sylvestris-Quercus-Betula forests, Pinus cembra-Larix-Betula forests). Because of the dry climatic regime, these continental communities are naturally more fire-prone than their oceanic counterparts north and south of the Alps. Some of the dominant taxa (e.g. Pinus sylvestris and Quercus) have evolved strategies for surviving fire injuries. Thus, in addition to the persistence of a continental climate in the inner valleys of the Alps (Tinner and Ammann 2001), the resilience to burning could have contributed to maintain these communities for thousands of years.

At 6500 yr ago the climate in the European Alps was probably 1.5°C warmer than today, and at most sites, the vegetation was rather different from modern plant communities. Most of the differencies are better explained by anthropogenic influence during various intrervals than by climatic change. Human activity generated low-competition niches in vegetation. Due to such niches, it seems that the modern vegetation in the Alps is partly in disequilibrium with climate. At the same time, marked societal and land-use changes occured during the last 50 years, so that forest vegetation is no longer in equilibrium with human activities [...].

The late-glacial and Holocene records (e.g. Ammann et al. 2000; Tinner and Lotter 2001) suggest that large-scale vegetation changes in the Alps occured when temperature variations exceeded 1.5-2°C. Temperature changes were often accompanied by precipitation variations and by strong and abrupt responses of vegetation. [...]

Observations
 
Modélisations
 
Hypothèses

[Due to low-competition niches in vegetation generated by human activities], it seems that the modern vegetation in the Alps is partly in disequilibrium with climate. At the same time, marked societal and land-use changes occured during the last 50 years, so that forest vegetation is no longer in equilibrium with human activities (e.g. Conedera et al. 1996). Thus, even under constant climatic conditions, large-scale replacement processes would probably occur during the next decades. [...]

The late-glacial and Holocene records (e.g. Ammann et al. 2000; Tinner and Lotter 2001) suggest that large-scale vegetation changes in the Alps occured when temperature variations exceeded 1.5-2°C. Temperature changes were often accompanied by precipitation variations and by strong and abrupt responses of vegetation. It is hence likely that, if the forecasted temperature increase should excedd 2-3°C, vegetation will respond rapidly, i.e. within a few decades. The modern situation, with vegetation neither in equilibrium with climate nor with human land-use, may amplify and complicate the compositional and structural adjustment processes to future climate change. To better address this issue, we need additional efforts in paleoecology and related fields [see details in the study...].


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

Bioclimatic limits of species distributions:
Environmental requirements of species (e.g. as input for ecological models) are usually derived from today's presence or absence in e.g. climatic space, rather than from experiments. However, this "biogeographical" approach may be distorted by prehistoric and historic human impact, which may result in a biased view of the potential range of a species. In the past, some species may have benefited from natural environments that did not persist untill today. These no-analogue environmental conditions may be used to provide additional information about the behaviour of species under changing and extreme climatic conditions. [...]

Responses modes of Alpine ecosystems to environmental changes:
Plant species interact with other organisms and with abiotic factors, so that the response of vegetation to climatic change and/or disturbances depends not only on the environmental requirements of the species, but also on interspecific competition and interference. Depending on the species involved and the agents forcing the environmental change or disturbance (magnitude, severity, frquencey), forest ecosystems may respond with "resilience", adjustment", or "vulnerability". New paleoecological results suggest that many vegetation types in the Alps responded with displacement (vulnerability) or adjustment during the past 6500 cal. yr [fig. 1], whereas only a few showed resilient behaviour on such long time scales; [...]

[The authors] summarize a few case studies on the effects of Holocene climate change and disturbance on the vegetation of the Western Alps. To categorize the main response modes of vegetation, [they] use three classes of ecological behaviour: "resilience", "adjustment", and "vulnerability". [They] assume a resilient (or elastic) behaviour if vegetation is able to recover to its former state, regaining important ecosystem characteristics, such as floristic composition, biodiversity, species abundances, and biomass. Conversely, vegetation displacements may occur in response to climatic change and/or disturbance. In some cases, this may culminate in irrevrsible large-scale processes such as species and/or community extinctions. Such drastic developments indicate high ecosystem vulnerability (or inelasticity or instability [Küttel 1990; Aber and Melillo 1991) to climatic change and/or disturbance. In this sense, the "vulnerability" (or instability) of an ecosystem is expressed by the degree of failure to recover to the original state before disturbance and/or climatic change. Between these two extremes (resislience vs. vulnerability), ecosystem adjustments may occur, including the appearance of new/or the disappearance of old species. The term "adjustment" is hence used to indicate the response of vegetationnal communities, which adapted to new environmental conditions without loosing their main character. For forest ecosystems, [the authors] assume vegetational adjustments (rather than vulnerability) if the dominant (or co-dominant) tree species are not outnumbrered or replaced by formerly unimportant plant species or new invaders. Adaptation as a genetic process is not discussed here [...].

If paleoecological sites are arranged according to their altitude, it is possible to reconstruct past forest-vegetation belts in order to assess the ecological potential of today's species under warmer (and moderately more continental) conditions, when human impact was still small. [...]


(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
 

Références citées :

Aber, J. D., and Melillo, J. M. (1991). "Terrestrial Ecosystems." Saunders College Publishing, Philadelphia.

Ammann, B., Birks, H. J. B., Brooks, S. J., Eicher, U., von Grafenstein, U., Hofmann, W., Lemdahl, G., Schwander, J., Tobolski, K., and Wick, L. (2000). Quantification of biotic response to rapid climatic changes around the Younger Dryas: A synthesis. Palaeogeography, Palaeoclimatology, Palaeoecology 159, 313-347.

Conedera, M., Marcozzi, M., Jud, B., Mandallaz, D., Chatelain, F., Frank, C., Kienast, F., Ambrosetti, P., and Corti, G. (1996). "Incendi boschivi al Sud delle Alpi: Passato, presente e possibili sviluppi futuri." vdf, Hochschulverlag ETH Zürich, Zürich.

Heiry, O. (2001). "Holocene paleolimnology of Swiss mountain lakes reconstructed using subfossil chironomid remains: Past climate and prehistoric human impact on lake ecosystems." Unpublished PhD thesis, University of Bern, Bern.

Küttel, M. (1990). Der subalpine Schutzwald im Urserental: Ein inelastisches Ökosystem. Botanica Helvetica 100, 183-197.

Tinner, W., Ammann, B., and Germann, P. (1996). Treeline fluctuations recorded for 12,500 years by soil profiles, pollen, and plant macrofossils in the central Swiss Alps. Arctic and Alpine Research 28, 131-147.

Tinner, W., Conedera, M., Gobet, E., Hubschmid, P., Wehrli, M. and Ammann, B. (2000). A palaeocological attempt to classify fire sensitivity of tress in the southern Alps. The Holocene 10, 565-574.

Tinner, W., and Ammann, B. (2001). Timberline paleoecology in the Alps. PAGES News 9, 9-11. [Fiche biblio].

Tinner, W., and Lotter, A.F. (2001). Central European vegetation response to abrupt climate change at 8.2 ka. Geology 29, 551-554.

Tinner, W., and Theurillat, J.-P. (in press). Uppermost limit, extent and fluctuations of the timberline and treeline ecocline in the Swiss Central Alps during the past 11,500 years. Arctic and Alpine Research