Contrasting Climate Change Responses of the Rare Moss Genus Tetrastichium (Mitt.) Cardot Across Macaronesia:...

Climate change poses a threat to bryophytes with restricted distributions and strong dependence on humid habitats. We assessed the climatic suitability of the moss genus Tetrastichium across the Azores, Madeira, and the Canary Islands. We compiled 90 records each for Tetrastichium fontanum and Tetrastichium virens and fitted Boosted Regression Tree models using WorldClim 2.1 bioclimatic predictors. Future suitability was projected for 2061-2080 and 2081-2100 using two global climate models under SSP3-7.0 and SSP5-8.5. Model performance was good (AUC = 0.88, sTSS = 0.81, and sensitivity ≥ 0.94). Under current and future conditions, suitable areas were unevenly distributed among archipelagos. Climatically suitable areas generally increased in the Azores but contracted substantially in Madeira and the Canary Islands. Under UKESM1-0-LL, no suitable areas in the Canary Islands remained above the climatic-suitability threshold by the end of the century. Spatial overlap between current and future predictions declined under stronger climate forcing and longer time horizons, being consistently higher for T. virens. These findings reveal the high sensitivity of Tetrastichium to climate change, identifying Madeira and the Canary Islands as areas of conservation concern. Protecting extant populations and environmentally buffered habitats will be essential for the genus's persistence under future climates.