Ground vegetation species richness in close-to-nature managed and protected forests after four decades of protection.

The aim of this study was to comprehensively evaluate how close-to-nature forest management influences species richness of plant in comparison to protected forests. We adopted a multi-scale framework integrating local (alpha), regional (gamma), and spatial turnover (beta) diversity, allowing us to disentangle contrasting species richness responses that may emerge depending on the scale of observation. Data from 671 plots were analysed to assess species richness of plant in protected forest areas and in close-to-nature managed forests of the Polish Western Carpathians. The forest communities within the study area are predominantly Carpathian beech-fir forests (Abies alba-Fagus sylvatica). To assess the effects of forest structure and management on local diversity, generalized additive models (GAMs) were applied. Analyses of gamma and beta diversity were conducted separately using rarefaction and turnover metrics, in accordance with the multi-scale framework of the study. Our results demonstrate that differences in plant diversity between management regimes depend strongly on the spatial scale of analysis. Managed forests exhibited higher plot-level (alpha) diversity. The enhanced local diversity in managed forests appears to be associated primarily with management-induced structural openness and vertical complexity rather than forest maturity per se. In contrast, protected forests supported higher gamma diversity and substantially greater beta diversity, reflecting stronger species turnover and the persistence of rare and specialist taxa associated with long-term continuity and environmental heterogeneity. Overall, our findings support close-to-nature forest management as an important component of multifunctional forestry, capable of conserving plant diversity when appropriately tailored to local ecological conditions. At the same time, they reaffirm the irreplaceable role of protected forests in maintaining regional biodiversity. Effective conservation strategies should therefore integrate both approaches, explicitly accounting for biodiversity patterns across multiple spatial scales.