Abstract ID: 3.13039 | Accepted as Talk | Talk/Oral | TBA | TBA

Treeline ecotones are extremely sensitive to multiple drivers and are generally considered as indicators of vegetation response to climate change. It is widely recognized that multiple factors in addition to climate drive the upward and poleward tree migration and that many other drivers act at finer spatial scales. Multi-scale approaches to better understand how the interaction of multiple drivers influences treeline position, its spatial patterns, and dynamics are needed. In a research conducted over 90 hectares of treelines divided in 10 sites and distributed across the Italian Alps, we have comprehensively stem-mapped the trees by integrating UAV and filed data collection. We here aim to provide valuable insights on the joint effect that several biotic and abiotic drivers have on the ecotone spatial patterns across the entire mountain range. The high-resolution ground cover classification obtained through a deep learning model was combined with fine-scale terrain features and topographic attributes, and with intra- and inter-specific relationships existing between coniferous and broadleaved species. The combination of the biotic and abiotic component was finally related to the spatial patterns of the treeline ecotones by using spatial and multivariate statistical tools (PPA, RDA, RF). Preliminary results highlight that tree establishment is majorly driven by ground cover, with grass and deadwood displaying a predominant role in driving the process. Apart for the heatload and the eastness, which displayed a direct, positive correlation with the seedlings presence, the other topographic variables did not show any particular influence. The presence of previously established trees in the close surrounding of a microsite seemed to have a negative effect on tree establishment, suggesting that competition prevails over facilitation in the studied ecotones. The applied setup aims at disentangling and giving a broader understanding of the role that different microsites and biotic interactions have on tree recruitment and survival at the upper tree limit. We expect our findings to explain the variability in treeline patterns and processes that macro- and mesoclimate factors alone cannot explain.