Towards a transdisciplinary framework for studying the DYNAMICS OF WOODY ALPINE VEGETATION in a WARMING CLIMATE CONTEXT
Résumé
Alpine ecosystems, defined here as high-elevation habitats within and above the treeline ecotone, have experienced particularly rapid warming in recent decades, triggering diverse and extensive vegetation responses with already noticeable consequences for biodiversity and ecosystem services. In the Alps, a widespread greening response of alpine ecosystems (similar to the Arctic greening) has been detected using remote sensing methods since the availability of satellite imagery in the 1980s, showing that alpine biomass is increasing1. Similar to the Arctic, we suspect that this greening is primarily driven by the increase in growth and cover of alpine shrubs2 (i.e. shrubification)
and the establishment of trees on alpine grasslands3, both phenomena that we will summarize under the term "woodyfication" of “alpine ecosystems. In fact, woodification can be explained by the new opportunities offered at the coldest edges of ecological distribution areas. However, field observations of woody vegetation (by diachronic aerial photo comparisons or dendroecology) show contradictory results. The response of trees and shrubs to temperature rise varies between positive and negative along topoclimatic gradients, which is exacerbated by the complexity of mountainous, rugged terrains4. On an even finer spatial and temporal scale, a closer look at the physiological response of trees and shrubs by observing variations in stem diameter (dendrometry) can help to identify different stress factors such as summer and winter drought that could offset the positive effect of temperature. Dendrometric studies show a very species-specific response and the importance of microclimate5.
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