Fires control spatial variability of subalpine vegetation dynamics during the Holocene in the Maurienne valley (French Alps)

Abstract

Due to stresses resulting from their high altitudes, subalpine forests are sensitive to disturbances, including fire. This study analyzes the long-term relationships between fire and subalpine vegetation in the western Alps. High-resolution analyses of charcoal, pollen, macroremains, and other palynomorphs were performed on sedimentary cores from 2 small peaty ponds located above 2000 m asl. in the Maurienne valley, France. Results reveal similar long-term vegetation dynamics, with differences concerning the structure and composition of local and surrounding plant communities. The vegetation pattern appears partially related to local fire occurrence, which was most frequent between 8900 and 6500 cal. BP at one lake and between 4100 and 1800 cal. BP at the second. Fires notably triggered the development and occurrence of populations of Acer and Alnus incana-type during a 2000-y period and the asynchronous alteration of Pinus cembra forests at both sites. Results show that the low-competitive species, i.e., Larix decidua or Pinus uncinata, were never stimulated by increasing fire frequency. This highlights the past importance of local-scale processes such as fire, which favoured pioneer broad-leaved species but did not threaten the resilience of the subalpine forests dominated by the cembra pine.