Influence of canopy structure and light on the three-dimensional distribution of the iconic lichen Usnea longissima

Forest canopies modify microclimates and create habitats for nonvascular epiphytes, but we need to better understand the mechanisms regulating their vertical horizontal distributions. Here examine how canopy structure light environment influence 3D distribution of Usnea longissima, world’s longest lichen, associated with old-growth forests. We quantified forest structure, profile (PPFD transmittance fraction), as well lichen in a 1 ha plot dominated by Picea abies. The had multi-layered mortality driven small-scale gap dynamics. population size an approximate log-normal host trees showing strong clustering. extended up mid-canopy rather sharp upper limit. Population increased DBH limit did not correlate basal area. was steeper dead than live trees, occurring zone low-intermediate light. linked through short-distance asexual dispersal. lichen’s shaped various interacting functional mechanisms. Its absence from mainly explained sensitivity high when desiccated limited capacity upward migration. dynamics source hosting large populations mid-canopy. association humid, forests is narrow niche preferences dispersal limitation, slow growth. Protection long continuity tree cover needed secure substrates suitable development viable populations. Our study highlights that lichens dynamics, microclimate, traits.