Beta diversity and species turnover in communities of newly recruited seedlings following forest management

Second-growth forests tend to have less native diversity compared to their older-growth counterparts. Forest management can be used to encourage diversity in young forests, enhancing resilience of these forests to various threats including pests and pathogens, as well as climate change. Understanding the impacts of forest management on spatial and temporal variability in newly establishing plant communities is key to predicting resultant patterns of biodiversity across the forest landscape. Two critical measures of the spatial and temporal aspects of biodiversity are beta diversity and species turnover. Beta diversity quantifies variability in species composition across space, while species turnover quantifies temporal changes in species composition. We monitored the impacts of two common forest management techniques (selective overstory thinning done alone and selective overstory thinning done in tandem with removal of nonnative shrubs, paired with unmanaged controls) on composition, beta diversity, and species turnover in communities of newly recruited woody seedlings within a second-growth forest in Northeast Ohio, United States of America. Management impacted the composition of newly recruiting woody seedlings in the first two years of study (2020 and 2021), though there was no signal of management treatment on community composition in the third (2022). We found that beta diversity was lower in areas with overstory thinning done in tandem with nonnative shrub removal, compared to forests with no management or managed with overstory thinning alone, indicating that variability in community composition across space was lower within these managed areas. Community composition of newly recruited woody seedlings varied across years (from 2020 to 2022) in plots managed with overstory thinning paired with nonnative shrub removal, as well as unmanaged plots. Interestingly, composition across these three years was relatively consistent in plots managed with overstory thinning alone. Species turnover from 2020 to 2022 did not differ across management treatments. Our findings indicate that management interventions - particularly the combination of overstory thinning and understory removal of nonnative shrubs - can significantly influence the composition and diversity of newly recruiting woody plant communities. Overstory thinning, on its own, proved to have little impact on the forest understory, instead requiring nonnative shrub removal as a critical component of forest management. However, due to high turnover of new recruits within the community, results can be variable from year to year. These shifts in composition suggest that management has the potential to alter the balance of species within the community and may ultimately drive biodiversity in managed forests.