Bryophytes play an important role in headwater stream ecosystems sensitive to human pressures. The high number of bryophyte species listed as threatened in Europe suggests that further efforts to conserve fluvial bryophyte diversity are needed. Investigations of the spatial ecology of bryophyte diversity should help identifying priority areas for conservation of fluvial bryophytes and their habitats.
Seasonal temperate headwater streams were sampled at their southern edge distribution in Portugal, within and outside protected areas, at two spatial scales: stream segments and microhabitats. The environmental variables best explaining richness and diversity patterns, as well as the number of threatened species, were identified by partial least square regression. The selection of the best sites for conservation was achieved through the development of a new Index of Fluvial Bryological and Hydrogeomorphological Signature (IFBHS).
At the stream segment scale, bryophyte community structure was highly influenced by hydrogeomorphological variables, in particular by hydrological features. At the microhabitat scale, high current velocity constrained bryophyte richness and diversity. The prioritised sites identified through the application of the IFBHS exhibited exceptional bryological richness, high levels of endemism and red-listed species, as well as unique fluvial microhabitats.
Hydrological regime was identified as a major environmental driver of bryophyte community structure in seasonal headwater streams of southern temperate Europe, and this is of particular concern given projected scenarios of climate change and human-induced flow regime alterations. Prioritised stream segments for fluvial bryophyte and habitat conservation were not only located within protected areas, reinforcing the need to enhance the effectiveness of Natura 2000 Network and national protection areas.