Re-envisioning urban landscapes: lichens, liverworts, and mosses coexist spontaneously with us

Abstract

Current conceptions of “urban biodiversity” address only particular taxa, ignoring the full richness of species within cities. Despite their exclusion from these conceptions, tree-dwelling lichens, mosses, and liverworts (collectively, “epiphytes”) are recognized as bioindicators of urbanization, but their inherent contributions to biodiversity are largely unrecognized. Here, we report on a survey of epiphytes in the city of Vancouver, Canada. Using Bayesian multilevel models, we asked the following questions: how diverse are epiphytes in this large temperate city, and what urban and host-tree factors determine their distribution? We found 39 macrolichen, 32 moss, and seven liverwort species on Vancouver street trees, establishing them as rich microenvironments influenced by a network of interacting factors previously unaccounted for. Our results challenge the idea that pollution and urban heat islands primarily regulate urban epiphyte diversity; instead, we identify host-tree genus as having strong effects on all epiphytes. Expanding urban biodiversity to include epiphyte diversity recharacterizes urban landscapes as rewilded spaces of interdependent coexistence.