Macroclimatic niche similarity and species relatedness shift their influence on species co‐occurrence in bryophyte forest communities across scales

The processes driving species co‐occurrence across scales are poorly understood. Bryophytes are especially interesting in this respect because, while they disperse over long distances and have broad distributions, they are particularly affected by local conditions due to their small size. We investigated the relationship between pairwise species associations within epiphytic bryophytes and their macroclimatic niche similarities and taxonomic relatedness at four scales (global, regional, habitat and microhabitat). We used community data for 2000 trees from 107 forests in the northwest Iberian Peninsula, and global occurrences for the 33 species with broad distributions, to calculate pairwise co‐occurrence at each scale and bioclimatic niche similarity. We also obtained taxonomic distance matrices from the bibliography as a proxy for pairwise phylogenetic relatedness between species. Co‐occurrence relates to macroclimatic niche similarity at all scales, but this relationship decreases towards smaller scales. Taxonomic affinity was also a good indicator of the pairwise co‐occurrence not explained by macroclimatic niche similarity at the finest scales. Interestingly, at all scales, most pairwise relationships are positive or neutral rather than negative, although the direction of approximately 7% of these relationships shifts from positive at the microhabitat scale to negative at the regional scale. Macroclimatic requirements are progressively less important for species coexistence as scale diminishes, probably due to the effect of unmeasured local interactions, community‐level processes, and microclimatic variations. Synthesis. Our results highlight that positive interactions may be at least as important as negative ones, if not more, for the coexistence of bryophyte species across scales. They also underscore that co‐occurrence patterns may shift across scales, and the critical role of both macro‐ and microenvironmental conditions in shaping the life strategies and persistence of local populations of a plant group with population dynamics characterized by extensive geographic distributions. The implications of these findings go beyond their relevance for bryophyte ecology, challenging the prevailing assumption that limiting similarity processes primarily shape ecological communities.