Using vegetation dynamics to face the challenge of the conservation status assessment in semi-natural habitats

The conservationof semi-natural habitatsrepresents a primary challenge for European nature conservationdue to their great species diversity and their vulnerability to ongoing massive land-use changes. As these changes rapidly transform and phase out semi-natural habitats, conservationmeasures should be prompt and specifically focused on a sound assessment of the degree of conservation. Here we develop a methodological strategy for the assessment of the degree of conservationof semi-natural grasslands based on well-defined criteria rather than on expert opinion. Through mixed effect models, we tested ten potential indicators, encompassing proxies of species composition, habitatstructure, and landscape patterns, against a measure of compositional change from habitatfavourable condition, i.e., an inverse proxy of conservation status. This measure derives from the re-visitation of 132 sampling units historically sampled between 1966 and 1992 along the Apennines. The compositional change was quantified as the dissimilarity between historical habitat species poolsand the composition of current communities. The compositional change was significantly related to the number of habitatdiagnostic species and the relative cover of woody species with opposite sign (positive and negative, respectively). We classified and combined the classes of these two indicators in each sampling unit to assess the habitatdegree of conservationat the plot and at the Natura 2000site level. At the plot level, our assessment was in good agreement with the occurrence of species of conservationconcern. On the other hand, at the site level, our assessment was not always harmonic with the habitat conservationassessment officially reported for the site investigated.