An experimental approach to identify drivers of tree regeneration diversity, composition, and heterogeneity in northern hardwood forests

Silviculture methods such as clearcutting, shelterwood seed cutting, and selection system are used to manipulate the canopy and regenerate new cohorts in hardwood stands. Additionally, site preparation can be utilized to alter seedbed conditions with the aim to promote changes in species composition. However, limited seed availability and increased ungulate browsing may limit successful natural regeneration in some areas. Our objective was to investigate the influence of regeneration method, site preparation, deer exclusion, and direct seeding on the regeneration of a managed northern hardwood forest. Utilizing a randomized split-plot design with three splitting levels, we examined the effects of four different regeneration methods, two site preparation treatments, seed limitation and deer browsing on composition, compositional heterogeneity, and richness of regenerating tree species. We observed significant differences in the resulting species composition related to the regeneration and site preparation methods. Shelterwood seed cutting implemented with 60% and 30% residual canopy cover, along with scarification, increased species richness and species compositional heterogeneity. However, the combination of deer exclusion and direct seeding resulted in the highest species richness across all treatment combinations. Deer exclusion alone did not enhance richness or compositional heterogeneity, highlighting the impeding effect of limited seed availability. We found that direct seeding successfully altered species composition and increased species richness. Our results suggest that while the regeneration and site preparation methods can benefit natural tree regeneration, approaches that also address both seed limitations and deer browsing will be necessary to increase the tree species diversity in some cases