Long-range avalanche-forest interactions leave strong environmental footprints in medium-high mountain ranges | Les interactions à long terme forêt / avalanche marquent durablement l'environnement dans les montagnes de moyenne et haute altitude.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Hydrosystèmes et risques naturels

International audience

Inglés. Unlike alpine-like high mountain ranges, medium-high mountain ranges are generally not considered to be avalanche-prone areas. However, when terrain and climate characteristics are favourable, significant avalanche activity can affect these environments, playing a major role in landscape structuring. Specifically, avalanche-forest interactions leave strong environmental footprints up to the immediate vicinity of te release areas. These interactions also control the landscape dynamics and are strongly linked with climate and anthropogenic drivers. The aim of this work is to refine our understanding of these complex processes representative of the deep changes undergone by sensitive systems submitted to rapid global changes. To this end, an avalanche-prone area representative of the Vosges Mountains - the avalanche complex of the Rothenbachkopf-Rainkopf 1316 m a.s.l. - was studied via a comprehensive multidisciplinary approach associating geo-history, forest ecology, remote sensing and climatology. Avalanche activity has been documented over more than 200 years using a combination of different sources: administrative archives, local press, scientific papers, iconographical documents, oral testimonies, etc. Land use and land cover evolution have been identified through the diachronic analysis of a large set of old maps and aerial photographs. In addition, the current state of the forest landscape has been characterized through field surveys and analysis of aerial laser scanning data. It first appears that forest stands show a clear longitudinal (upstream-downstream axis of the avalanche paths) and transverse (from the center to the margin of avalanche paths) structure. This pattern of tree species, sizes and morphologies form 'avalanche landscapes' in near-equilibrium with the frequency/intensity of avalanche activity. From a dynamic point of view, diachronic analyses reveal that avalanches of high intensity (multi-decadal return period) regularly destroy large parts of the forest stands, inducing quasi-cyclic changes in the landscape mosaic. However, changes in sylvo-pastoral practices and climate warming have led the study site to evolve towards almost total forest colonization over recent decades. Outlooks include a refined characterization of avalanche activity using tree-ring techniques and how it relates to the characteristics of the forest stands (species, ages, sizes, shapes, number and type of growth disturbances, etc.).