High Temporal Beta-Diversity of Pollinators in Early Successional Forests After Windthrow.

Forest windthrows have generally a positive effect on the biodiversity of understory vegetation and on insects associated with open conditions, such as pollinators. However, the early successional stage after forest disturbances can be highly heterogeneous in both space and time. While most of the available literature has focused on finding spatial patterns of biodiversity in relation to the disturbed environment, few studies have measured the temporal changes occurring in wind-affected forests, especially within the early successional stage. Here, we focused on describing the temporal dynamics of vascular plants and pollinators by sampling the same sites after 3 and 5 years from a major storm event (Vaia) in the Italian Alps. We observed high values of temporal β-diversity for all pollinator taxa, with species belonging to Diptera, i.e., hoverflies and tachinids, experiencing the highest temporal community change, followed by Hymenoptera (wild bees). Conversely, the temporal change in the understory plant communities was the lowest. For all studied taxa, the temporal dynamics were mostly driven by the turnover of species in the assemblages, indicating that colonising species largely replaced original species. Furthermore, we detected an important component of species gain over time in the pollinator communities, while plant communities experienced little net species change. Although we did not find significant environmental patterns explaining the overall temporal community dissimilarity, we found that mountain topography may drive some components of temporal change, especially for the dipteran communities. Our results indicate that organisms with higher ecological and trophic requirements experience higher species turnover in early successional forests, as these evolve over time. We stress the importance of monitoring arthropod assemblages in disturbed forests and suggest to carefully evaluate single-year studies for management and conservation purposes.