Short-term responses of overstory and understory vegetation to thinning treatments: a tale of two studies

The Density Management Study and Young Stand Th inning and Diversity Study were initiated to investigate whether alternative thinning treatments can accelerate the development of forests toward late-successional structures. An overview of overstory and understory vegetation responses indicates that the magnitude and direction of thinning eff ects initially varied among structural stand components. Average crown length, diameter growth, and seedling and sapling density increased rapidly after thinning. However, diameter growth of the largest trees was less responsive to thinning, at least in the short term. Overall shrub cover was initially reduced by thinning, which was likely a consequence of harvesting damage. Th inning tended to increase overall species diversity by benefi tting early-successional species, and had little infl uence on late-successional species diversity. This trend appeared to reverse itself quickly, as early-seral vegetation declined within a decade. It appears that silvicultural treatments may best target specific stand structural components, e.g., large trees, crown length, or an understory shrub layer, rather than attempting to achieve all late-successional structural elements simultaneously. Increasing variability at smaller and larger spatial scales may be an option to achieve multiple management goals.