Extending the interpretation of Natura 2000 habitat types beyond their definition can bias their conservation status assessment: An example with species-rich Nardus grasslands (6230*)

In this study, taking as an example the species-rich Nardus stricta grasslands (habitat 6230*) within the Natura 2000 network of the Lombardy region (northern Italy, central southern Alps), we evaluated i) whether the spatial distribution of the habitat 6230* corresponded to essential features for its identification, and ii) whether a broad habitat interpretation could affect its regional conservation status assessment. We analysed the spatial distribution of habitat 6230* regarding the elevation, geological substrate, forest treeline, land use types and other habitat types. Using the regional database of habitat relevés, we calculated the threshold values of conservation status for a range of indicators of structure, functions and future prospects. To this end, we used a subset of relevés of the subalpine sub-type of habitat 6230*, as it corresponds to plant communities where habitat interpretation can easily be extended beyond its definition. The mapped distribution of habitat 6230* did not entirely match the essential features required for its identification. Some polygons were located at the ecological extremes of habitat 6230*, on carbonate substrates and in the alpine belt. In those conditions, the habitat showed an Unfavourable-bad (U2) conservation status, decreasing species richness and typical species dominance and frequency. Our findings highlighted that plant communities representing ecological extremes of the habitat type 6230* should no longer be referred to the same habitat type. The proposed indicators can help identify habitat sub-types more conducive to successful restoration measures, thereby ensuring favourable conservation status. In turn, this guarantees sustainable agricultural land use, which simultaneously promotes biodiversity and high-quality food products. Furthermore, the procedure could be extended to other habitat types for early identification of priority monitoring areas, especially when their interpretation has gone beyond their definition, with little consideration given to the consequences on the regional conservation status assessments.