Bridging Conservation Gaps: Evaluating Habitat Mapping Methods for Alpine River Ecosystems.

Natural habitats are globally threatened and fragmented, posing challenges for dynamic ecosystems dependent on ecological processes and intact habitat networks. Our study, therefore, examines the implementation of the European Union's Habitats Directive in safeguarding the habitat type "Alpine rivers with their ligneous vegetation with Myricaria germanica". Using Bavarian and Austrian mapping guidelines, alongside simple and habitat suitability models, we identified disparities and limitations in current habitat delineation methods. Our findings reveal substantial inconsistencies between the Bavarian and Austrian mapping guidelines and the species' potential habitat predicted by the habitat suitability model. The Bavarian method overestimates the extent of the habitat type by also classifying areas in advanced successional stages as such, covering 88% of the study area. Habitat suitability modeling shows this exceeds the suitable habitat by up to 74%. Compared to the more selective Austrian method, the Bavarian method maps 14 times more area. The Austrian method focuses on the current habitat occupancy of M. germanica, a crucial factor in detecting changes in distribution and habitat quality in dynamic river systems. However, monitoring pioneer, pre- and sub-successional habitats alongside existing populations is essential to fully protect metapopulation dynamics. Habitat Suitability Modeling offers an opportunity to complement field surveys for this purpose. Our findings further highlight the need for more consistent cross-border mapping and standardized assessment criteria to accurately track habitat changes, supporting effective implementation of instruments such as the Nature Restoration Regulation and ensuring long-term conservation and restoration of dynamic ecosystems.