Geomorphological and functional determinisms of plant distribution in high-altitude ecosystems: an essay of eco-geomorphology. Implications and applications to biodiversity restoration of ski trails.
Restoration of degraded high-altitude ecosystems takes place in conditions where both vegetation, soil and relief have been intensely disturbed. Consequently, restoration often fails to recreate a structure and functioning close to the original ecosystem. Even though, in mountain, it is known that vegetation is organised with relief forms, the underpinned mechanisms are misunderstood. To better manage establishment and dynamics of the vegetation, we propose a model that links constraints determined by the relief to adaptative characteristics of plant functioning. Plant functional traits identification and measurements at their different life stages help us to determine those characteristics. Elsewhere, we suppose that relief induce variations in climatic and soil factors, biotic interactions (competition, predation), as well as constraints related to geomorphological processes (erosion/sedimentation). Studies are conducted in subalpine zone (la Plagne, Northern French Alps), and mountain level (le Saignon, Southern French Alps). The first part, shows variation in biological traits involved in resource use, response to grazing and regeneration, with mesotopographical gradient. This one closely determines temperature cycles, soil resource level, grazing pressure, and snow pack duration. Studies of the second part analyse biological traits in relation with geomorphological processes. Slope determines dispersal of seeds at the soil surface. The extent of seed movements is strongly related to seed shape, and to the presence of two types of seed traps: (a) soil mounds close to the plant and generated by a barrier effect on sediment, (b) hoof prints of large herbivores. Studies in the part three, show that these traps also facilitate plant recruitment. Seed bank analysis reveals that abundance of seed in the traps is different in function of seed shape. Elsewhere, an experimentation points up that the germination and the seedling performance are affected by soil chemistry, and depend moreover of the plant functional type. In the fourth part, modelling approach and experimentation explore relationships between functional traits and competitive performance. Results show that plant distribution in the community is linked with soil resource availability and plant traits involved in resource use. To conclude, we propose the application of an eco-geomorphological model in the context of high altitude ecosystems. This model enlarges the view of traits/environment and species/habitat relationships. This provides a special way to analyse and apply restoration in high-altitude ecosystems.