Projected shifts in deadwood bryophyte communities under national climate and forestry scenarios benefit large competitors and impair small species

Aim Climate change and habitat loss are the main threats to forest biodiversity. Deadwood bryophyte communities are composed of species with different functional traits and are affected by these processes. Grouping species depending on their traits can help to anticipate community responses to global change, and to potential conservation actions. Location National scale of Sweden. Taxon Deadwood bryophyte species (15 liverworts and 8 mosses). Methods Generalized linear mixed-effects models were applied to test for differences in projected relative changes in habitat suitability (matching species' requirements) among species with contrasting traits under varying climate and forest scenarios during the years 2020-2100. Projections were based on ensembles of species distribution models (GLM, Poisson point-process, MaxEnt), climate scenarios and national scenarios of forest management and conservation. Results Shoot length was the best predictor of projected future changes in habitat suitability. Habitat suitabilities for small, short-lived species will decline in a warmer and wetter macroclimate, whereas those for large, perennial species will increase. We expect stronger habitat suitability decreases for obligate than for facultative deadwood species. Increasing the proportion of set-aside forests from 16% to 32%, and reducing the harvest levels in production forests, mitigated negative habitat trends of several sensitive species. However, the potential benefits of increased conservation were even larger for species with traits favoured by climate change, suggesting that these actions will also enhance the spread of these species. Main conclusions Climate change is expected to lead to shifts in boreal bryophyte communities towards large, competitive species and to an overall decrease in diversity. High investment in conservation actions seems necessary to maintain diversity. This should include increasing the area of forest set aside beyond 16%, and reducing harvest levels in production forests. However, whilst these actions may prevent species extinctions, at least in the short term, changes in community structure seem inevitable