Uncovering drivers of epiphytic cryptogam diversity in forest ecosystems through a functional trait approach

Forest biodiversity, including often-overlooked cryptogams, such as epiphytic lichens, bryophytes, free-living algae, and fungi, underpins the fundamental processes that sustain ecosystem functions. In the face of growing climatic and habitat-related changes, it is crucial to understand how shifts in environmental conditions affect biological communities and, in turn, reshape ecosystem functions. Achieving this requires insight into the drivers of spatial and temporal variation in both taxonomic and functional diversity. In our study, we employ a trait-based framework to quantify taxonomic richness and functional diversity of epiphytic non-vascular communities across ten forest sites in the Italian ICP Forests Level II network, representing nemoral, boreal, and Mediterranean forest types. We investigate biotic traits of recorded taxa (growth form, thallus colour, secondary metabolite profile, reproductive strategy, and thermal- and water-related traits) and relate them with key environmental predictors (macroclimatic variables, sub-canopy microclimate, and stand structure). In addition, with particular focus on symbiotic organisms, we examine both spatial patterns and temporal trends in lichen diversity and identify their key drivers based on data obtained by repeated surveys conducted within the period 2005 – 2024. More than 200 lichen taxa have been recorded and analysed using alpha and beta diversity metrics. This integrative approach clarifies how cryptogam communities respond to environmental variation and provides a scientific basis for conservation planning aimed at sustaining ecosystem services under ongoing global change