Holocene vegetation responses to fire events in the inner French Alps (Queyras Massif): data from charcoal and geomorphological analysis of travertine sequences

Travertines are calcareous deposits that result from water stream saturation in bicarbonate; they are extremely sensitive to environmental variations. Homeostatic conditions, such as a good development of vegetation and regular river flow, induce the formation of homogenous travertine facies enclosing plant imprints. Significant climatic changes and/or human perturbations may disturb the carbonate deposit favouring an increase in detrital material often rich in charcoal remains. Travertine systems located in the Queyras Massif (Aigue Agnelle and Peynin valley) provided abundant charcoal material; its analysis allowed us to identify five vegetation phases between c. 8400 and 1709 cal. yr BP, and to ascertain Holocene vegetation responses to fire perturbation. An ecological dynamic based on forestfire events is proposed. During periods of reduced fire frequencies (long-term fire cycle), Pinus cembra dominated the Queyras Massif vegetation. The predominance of travertine facies during these phases corroborates this interpretation. Periods of increased fire frequency triggered the development of Larix decidua/Picea abies (short-term fire cycle). This vegetation change was concomitant with the deposition of thick detrital layers resulting from slope erosion, as a consequence of recurrent fire perturbations. The permanent settlement in this region of human communities since c. 4400 cal yr BP favoured the development of Larix decidua/Picea abies. Finally, our results suggest that the collapse of agropastoral activities since AD 1950 might progressively lead to the regeneration of Pinus cembra.

[1]  M. Geurts,et al.  Les travertins de Coal River Springs : physico-chimie des eaux , 2007 .

[2]  Adam A. Ali,et al.  Subalpine Vegetation Dynamics in the Southern French Alps during the Holocene: Evidence from Plant Imprints and Charcoal Preserved in Travertine Sequences , 2004 .

[3]  Adam A. Ali,et al.  The Early Holocene treeline in the southern French Alps: new evidence from travertine formations , 2003 .

[4]  J. Guiot,et al.  Reconstruction and palaeoclimatic interpretation of mid-Holocene vegetation and lake-level changes at Saint-Jorioz, Lake Annecy, French Pre-Alps , 2003 .

[5]  Adam A. Ali,et al.  Holocene palaeoenvironmental changes in southern France: a palaeobotanical study of travertine at St-Antonin, Bouches-du-Rhône , 2003 .

[6]  M. Thinon,et al.  Études pédoanthracologiques des variations de la limite supérieure des arbres au cours de l’Holocene dans les alpes françaises , 2002 .

[7]  C. Ravazzi.  Late Quaternary history of spruce in southern Europe , 2002 .

[8]  Yves Bergeron,et al.  Change of fire frequency in the eastern Canadian boreal forests during the Holocene: does vegetation composition or climate trigger the fire regime? , 2001 .

[9]  B. Talon,et al.  Soil Carbon Sequestration by Holocene Fires Inferred from Soil Charcoal in the Dry French Alps , 2001 .

[10]  M. Conedera,et al.  A palaeoecological attempt to classify fire sensitivity of trees in the southern Alps , 2000 .

[11]  M. Ohlson,et al.  Interpretation of the charcoal record in forest soils: forest fires and their production and deposition of macroscopic charcoal , 2000 .

[12]  Y. Veyret.  J. Riser (Dir) Le Quaternaire géologie et milieux naturels , 2000 .

[13]  C. Carcaillet.  A spatially precise study of Holocene fire history, climate and human impact within the Maurienne valley, North French Alps , 1998 .

[14]  F. David.  Vegetation dynamics in the northern French Alps , 1995 .

[15]  Séverine Fauquette,et al.  Histoire de la végétation forestière d'un site du Briançonnais: le Lac de Cristol (Hautes-Alpes, France). , 1995 .

[16]  S. Bortenschlager,et al.  Human impact on the Holocene forest line in the Central Alps , 1993 .

[17]  M. Magny,et al.  Solar Influences on Holocene Climatic Changes Illustrated by Correlations between Past Lake-Level Fluctuations and the Atmospheric 14C Record , 1993, Quaternary Research.

[18]  F. Magnin,et al.  Les travertins; accumulations carbonatees associees aux systemes karstiques, sequences sedimentaires et paleoenvironnements quaternaires , 1991 .

[19]  F. Schweingruber.  Anatomy of European woods. , 1990 .

[20]  C. Burga.  Swiss vegetation history during the last 18 000 years , 1988 .

[21]  J. Clark.  Particle Motion and the Theory of Charcoal Analysis: Source Area, Transport, Deposition, and Sampling , 1988, Quaternary Research.

[22]  R. Wein,et al.  Bog profile evidence of fire and vegetation dynamics since 3000 years BP in the Acadian Forest , 1987 .

[23]  M. Brotto.  Karst de gypse et accumulations de tufs en Queyras , 1986 .

[24]  H. Lamb,et al.  CLIMATE AND HISTORY , 1980 .

[25]  P. Greguss.  Identification of living gymnosperms on the basis of xylotomy , 1955 .