Étiquette : Article scientifique

ARTICLE SCIENTIFQUE

Biogeomorphological interactions of vegetation for sediment storage on a
fine-grained active scree slope in a cold temperate maritime climate

AUTEUR
Daniel Germain | professeur - Département de géographie UQAM

Revue Geomorphology | numéro 455 (2024) 109201

Résumé (en anglais)
Vegetation colonization is known as an effective process for stabilizing talus slopes, but little quantitative data is available about the relationships between vegetation, sediment fluxes, and sediment storage. The results of a detailed analysis of a single active fine-grained scree slope show that the upper section, scattered with shrubby vegetation, represents an environment characterized by strong biogeomorphic feedbacks. Engineering species (Thuya occidentalis, Betula papyrifera, Cornus sericea, Salix caprea) are well adapted to high sediment mobility with different modes of reproduction and survival. White cedar has a high sediment trapping capacity (>22 m3 per individual) and generates a micro-relief of 80 cm on average. It is responsible for 99 % of the volume of sediment trapped by shrub vegetation, even though it represents 44 % of the total shrub population sampled. In contrast, the hardwoods species have a very low capacity for sediment trapping (<1 m3 per individual) and micro-relief generation (>20 cm). This is likely due to the morphology of the growth which, despite a strong capacity to produce stump rejections, remains limited in trapping sediment. The shrubby vegetation directly influences the trajectory of frost-coated clast flows, the dominant slope process. Nevertheless, the vegetation appears to be quite resilient and stable on a decadal scale, where even the occurrence of extreme debris flows had little impact. In the downslope section, the debris flows, frost-coated clast flows, and snow avalanches present original and circumstantial modalities of tree-line regression. If the upper slope remains of sufficient size to allow for the occurrence of high-magnitude geomorphic events, the tree line appears to be driven primarily by slope processes rather than climate. Although it may be surprising that recent warming lowers the tree line on the studied talus slope, this provides new insight into the complex and non-linear relationships between vegetation and talus slope processes.