A trait based approach as a conservation tool for protected species: the case study of Trifolium saxatile in the Gran Paradiso National Park

Studies based on functional traits are valuable tools for monitoring the conservation status of plant species. They facilitate the development of ecological models, helping to understand species niches and distribution and to predict responses to climate change. This study investigated Trifolium saxatile, a species of Community interest (Habitats Directive, Annex II) endemic to the Alps. Our research focused on exploring the intraspecific trait variation of T. saxatile across 10 populations within the Gran Paradiso National Park. We measured vegetative traits such as plant height, length, and number of inflorescences, for 995 individuals. Additionally, leaf traits were measured for 175 individuals, and for each population, we calculated the CSR strategy. For each sampling site 11 environmental variables, putatively influencing species occurrence and performances, were collected (elevation, slope, aspect, meso- and microtopography, vegetation cover, and percentages of rockiness and sand, debris, litter, and bare soil ). Through statistical analyses and ecological modeling, we linked functional traits and the geomorphologic feature of the habitat of the species, aiming to identify the key ecological factors influencing its niche and distribution. Our results suggested that T. saxatile prefers areas with sparse vegetation cover and a medium-to-high amount of rock and debris. Additionally, CSR classification suggests that T. saxatile favors ruderal and stress-tolerator strategies, although a clear boundary between the two was not evident. Indeed, the populations we analyzed tend to lean toward the stress-tolerator strategy, while still maintaining a broad continuum of variability. Altogether, this information seems to suggest a preference for sites with a discrete level of natural disturbance and scarce competition. This is the first time this preference has been proposed for this species, based on data derived from functional traits and we hypothesize that T. saxatile is not necessarily an opportunistic species. However, its ecological niche requires further investigation. Altitude and slope were identified as critical factors for T. saxatile distribution and deserve further analyses in relation to its functional traits. This could provide a better understanding of the distribution of its populations. The approach implemented in the present analysis allows not only assessing the current conservation status of T. saxatile but also provides a valuable benchmark to evaluate the species' ecological plasticity and adaptability, in the context of climate change. By gaining a deeper understanding of its ecological strategies and habitat preferences, local authorities, such as the Gran Paradiso National Park, will improve monitoring and conservation strategies which are mandatory for this species of community interest.