Réf. Tinner & Kaltenrieder 2005 - A

Référence bibliographique complète

TINNER, W., KALTENRIEDER, P. 2005. Rapid responses of high-mountain vegetation to early Holocene environmental changes in the Swiss Alps. Journal of Ecology, Vol. 93-5, 936–947.

 

Abstract: (1) The Early Holocene sediment of a lake at tree line (Gouillé Rion, 2343 m a.s.l.) in the Swiss Central Alps was sampled for plant macrofossils. Thin (0.5 cm) slices, representing time intervals of c. 50 years each from 11 800 to 7800 cal. year BP, were analysed and the data compared with independent palaeoclimatic proxies to study vegetational responses to environmental change.

(2) Alpine plant communities (e.g. with Salix herbacea) were established at 11 600–11 500 cal. year BP, when oxygen-isotope records showed that temperatures increased by c. 3–4 °C within decades. Larix decidua trees reached the site at c. 11 350 cal. year BP, probably in response to further warming by 1–2 °C. Forests dominated by L. decidua persisted until 9600 cal. year BP, when Pinus cembra became more important.

(3) The dominance of Larix decidua for two millennia is explained by dry summer conditions, and possibly low winter temperatures, which favoured it over the late-successional Pinus cembra. Environmental conditions were a result of variations in the earth's orbit, leading to a maximum of summer and a minimum of winter solar radiation. Other heliophilous and drought-adapted species, such as Dryas octopetala and Juniperus nana, could persist in the open L. decidua forests, but were out-competed when the shade-tolerant P. cembra expanded.

(4) The relative importance of Larix decidua decreased during periods of diminished solar radiation at 11 100, 10 100 and 9400 cal. year BP. Stable concentrations of L. decidua indicate that these percentage oscillations were caused by temporary increases of Pinus cembra, Dryas octopetala and Juniperus nana that can be explained by increases in moisture and/or decreases in summer temperature.

(5) The final collapse of Larix decidua at 8400 cal. year BP was possibly related to abrupt climatic cooling as a consequence of a large meltwater input to the North Atlantic. Similarly, the temporary exclusion of Pinus cembra from tree line at 10 600–10 200 cal. year BP may be related to slowing down of thermohaline circulation at 10 700–10 300 cal. year BP.

(6) Results show that tree line vegetation was in dynamic equilibrium with climate, even during periods of extraordinarily rapid climatic change. They also imply that forecasted global warming may trigger rapid upslope movements of the tree line of up to 800 m within a few decades or centuries at most, probably inducing large-scale displacements of plant species as well as irrecoverable biodiversity losses.

 

Mots-clés

Climate change - Larix decidua - Long-term timberline dynamics - Macrofossil analysis - Palaeoecology - Pinus cembra - Vegetation history

 

Organismes / Contact

Section of Palaeoecology, Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland

 

(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 (moisture)

Vegetation

 

Early Holocene: 11 800 to 7800 cal. year BP

 

Pays / Zone

Massif / Secteur

Site(s) d'étude

Exposition

Altitude

Période(s) d'observation

Swiss Alps

 

Gouillé Rion

 

2343 m a.s.l.

 

 

(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

Conclusions

Comparison with the general course of oxygen-isotope records from the Alps suggests that, within the limits of our time resolution (50 year) and precision, tree line vegetation was in dynamic equilibrium with climate, even during periods of extraordinarily rapid climatic change. In general, timberline position was very sensitive to temperature changes (e.g. at 11 500, 10 400 and 8400–8200 cal. BP), whereas vegetation composition in the Gouillé Rion area was mainly a result of air and soil-moisture conditions in response to high summer radiation. Vegetation patterns at Gouillé Rion appear to be due to a combination of extreme environmental conditions and a range of factors causing high climatic variability over both long-term and decadal scales.

Observations

 

Modélisations

 

Hypothèses

These data confirm previous reports of the high sensitivity of vegetation to changing climatic conditions (e.g. Ammann et al. 2000; Tinner & Lotter 2001) and imply that the predicted global warming of 1.4–5.8 °C may trigger large-scale displacements of plant species as well as rapid upslope movements of tree line. Such rapid changes would be especially dangerous for alpine biodiversity, given the already restricted extent of high mountain habitats. As emphasized by Overpeck et al. (2003), palaeoecological studies may be able to contribute to our understanding of responses to rapid climatic change and thus help to avert an unprecedented ecological disaster in the Alps and elsewhere.

 

Sensibilité du milieu à des paramètres climatiques

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

 

 

 

(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 :

Ammann, B., Birks, H.J.B., Brooks, S.J., Eicher, U., von Grafenstein, U., Hofmann, W. et al. (2000) Quantification of biotic responses to rapid climatic changes around the Younger Dryas – a synthesis. Palaeogeography, Palaeoclimatology, alaeoecology, 159, 313–347.

 

Overpeck, J., Whitlock, C. & Huntley, B. (2003) Terrestrial biosphere dynamics in the climate system: past and future. Paleoclimate, Global Change and the Future (eds K.D. Alverson, R.S. Bradley & T.F. Pedersen), pp. 81–103. Springer, Berlin.

 

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