Can Irregular Shelterwoods Confer a Competitive Advantage to Oaks? Evidence from an Eight-Year Gap-Based Regeneration Study in Kentucky, USA

Oak-dominated forests in the eastern US face persistent regeneration challenges due to competition from shade-tolerant and shade-intolerant species. Irregular shelterwoods have been proposed as an alternative to uniform shelterwoods to create microclimatic gradients favorable to mid-tolerant species such as oak. This study quantified regeneration dynamics eight years after establishing 60-m diameter silvicultural gaps in mature oak stands. Twelve experimental units were sampled along gap–edge–matrix transects, with half receiving midstory removal in the forest matrix surrounding the gaps. Generalized additive models showed that distance from gap center significantly influenced oak height, which declined sigmoidally from gap center into the matrix, while midstory removal had no significant effect on oak height or density. Our analysis revealed strong species-by-distance interactions for height and density. Oaks attained greatest height near gap centers but were overtopped by yellow-poplar and outnumbered by red maple across all locations. Oak competitiveness was most evident near gap edges; however, canopy recruitment remains uncertain given competitor size and density. Results indicate that the study’s treatments promoted oak advance reproduction but did not eliminate competitive disadvantages, suggesting that the proposed microclimatic benefits of irregular shelterwood practices alone may be insufficient to ensure oak recruitment and persistence through stem exclusion.