Natural forest remnants as refugia for bryophyte diversity in a transformed mountain river valley landscape

Riparian forests are among the most threatened ecosystem types worldwide. Their exploitation and replacement by coniferous plantations affects species pools and contributes to loss of biodiversity. We aimed to investigate bryophyte species pools within different habitat types in a transformed mountain river valley. We especially focused on the contribution of habitat types (relative to their proportional cover) to the species pool of the whole area. The study was conducted along the Czerwona Woda river - a model stream in the Stołowe Mountains National Park (SW Poland, study area: 91.2 ha) - and an example of coniferous plantations replacing natural broadleaved forest vegetation. Our study revealed the presence of 147 bryophyte species. The most valuable habitats in terms of diversity of bryophyte assemblages were remnants of the natural vegetation - broadleaved forests and streams. These habitats, constituting <5% of the study area, hosted ca 40% of the total species pool (61 and 62 species, respectively), while the species pool of Picea abies forests (92 species) was proportional to cover of this habitat type (ca 60%). Remnants of natural vegetation were hotspots of bryophyte diversity within the heavily altered landscape, and may play a future role as sources of recolonization by forest specialists. Our study also confirmed the important role of riparian areas in maintaining bryophyte species diversity at the landscape scale. The river valley studied contributes >20-fold more to the bryophyte species pool of the whole national park than indicated by its size. Thus, river valleys require special treatment - conservation based on natural restoration, and should remain reserved from wood production, as areas providing a wide range of ecosystem services.