The interaction between elevational gradient and substratum reveals how bryophytes respond to the climate

Questions Why does bryophyte richness increase along the elevational gradient? Even though a number of studies have documented the peculiar positive (or hump‐shaped) relationship between species richness and elevation in bryophytes, it is still unclear which underlying mechanisms cause the pattern. Location Norway spruce forests, Italian Alps, South Tyrol. Methods Eight gradients from 900 to 1900 m a.s.l. and three different substrata (forest floor, deadwood, tree trunks) were examined. Three responses from the bryophyte communities were analysed: species richness of mosses and liverworts, functional diversity (considering the morphological characteristics of species) and β‐diversity (separating the two components: richness difference and species turnover). Results On deadwood and tree trunks a quadratic relationship was found between bryophyte richness and elevation, but not on the forest floor. On all three substrata, the moss assemblages along the elevational gradient were dominated by the turnover process and not by the richness component of β‐diversity. In liverworts, the two components of β‐diversity were equally important. Temperature was the most important predictor of bryophyte richness, whereas model selection suggested that temperature, solar radiation and rainfall had equal effects on functional diversity. Conclusions The substrata affect the response of bryophytes to the elevational gradient. The bryophyte assemblages inhabiting the forest floor, being less subject to climatic variability than deadwood and tree trunks, could be less affected by the temperature increase where climate change is occurring.