Partizione additiva della diversità come criterio per la selezione di aree protette: un esempio per la rete di riserve naturali della Provincia di Siena

Abstract: Additive partition of diversity as standard for the selection of protected areas: the natural reserves network of the Siena province (Italy). Estimating the effects of the spatial components on species diversity represents an important step to establish the conservation “capacity” in a network of protected areas. A clear evaluation on how α, β, and γ diversity are partitioned among and within spatial (and temporal) scales can help us to drive managing decisions and provide methods for monitoring species diversity. Moving from these concepts, a probabilistic sample was applied here: (1) for quantifying plant species diversity at different spatial scales within the network of protected areas existing in the Siena Province (Central Italy); and (2) to evaluate the effects on the species diversity of the whole network due to the addition of two new protected areas (Ripa d’Orcia and Bogatto). Focusing on both common species and those defined as “focal” (included in regional, national or continental “red” lists), our results indicated that species richness of the protected areas differed each other independently from the sampling efforts. Diversity partitioning indicated that most of the diversity within the network is due to larger-scale β-diversity, i.e., the differences in species composition among reserves. Moreover, total β-diversity was decomposed into two components: βarea (due to the differences in area among reserves) and βreplacement (due to the compositional differences across protected areas). βarea was particularly important for all species, while βreplacement was the most important factor for the set of focal species. Noteworthy, the analyzed variation in diversity components due to the inclusion of the two new natural reserves into the network (Ripa d’Orcia and Bogatto) resulted in a proportional increase in βArea for the whole network, and, on the other hand, in a reduction for βreplacement diversity component. Based on these quantitative results, criteria for the selection and the inclusion of protected areas in existing networks of natural reserves (such as the Natura 2000 Network) can be achieved.