Assessment of Diversity and Evenness of Herbaceous Vegetation and Natural Regeneration Communities in the Plaiul Fagului Reserve

Environmental changes and anthropogenic pressures significantly influence both the tree layer and natural regeneration within forest ecosystems. Protected areas represent essential territories for the maintenance and conservation of species within forest communities. In this context, the present study aims to develop a methodological framework for the integrated application of diversity, evenness, and dominance indices in the study of forest plant communities. Analyses were conducted at both α- and β-diversity levels, providing a methodological basis for characterizing local diversity and community differentiation. Species diversity was estimated using the Shannon–Wiener (H′) and Simpson (D) indices, while evenness and dominance were assessed using the Pielou (J′) and Berger–Parker (d) indices. Differences among communities were quantified using the Bray–Curtis dissimilarity index and its components, turnover and nestedness, and structural convergence of forest communities was analyzed through the ICF. The results indicate that α-diversity, estimated by H′, ranges from low to moderate, suggesting a relatively uniform distribution of species abundance. In certain microhabitats, processes of diversification and oligodominance are observed. At the β-diversity level, the analyzed communities are characterized by high dissimilarity, mainly driven by species turnover and, to a lesser extent, by nestedness associated with species loss. The ICF highlights that these forest communities exhibit relatively high structural uniformity, characteristic of mature stands in ecological equilibrium.