THE RESPONSE OF REGENERATION TO OVERSTORY RETENTION IN HARVESTED MIXED-OAK STANDS

Open Access
Author:
Gilbert, Carrie Leigh
Graduate Program:
Forest Resources
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 05, 2009
Committee Members:
  • Kim C Steiner, Thesis Advisor
  • Eric Zenner, Thesis Advisor
  • James Craig Finley, Thesis Advisor
Keywords:
  • overstory retention
  • pennsylvania forests
  • oak regeneration
Abstract:
Long-term overstory retention after harvesting can affect regeneration development in harvested stands. The level of overstory retention influences the regeneration species composition and may decrease its growth and vigor through shade and resource competition. Retaining overstory trees in harvested stands may represent foregone economic opportunities, but serves other objectives, such as aesthetic, biodiversity, and wildlife habitat values. Pennsylvania’s Department of Conservation and Natural Resources developed and employs guidelines for long-term overstory retention in even-aged regeneration harvests. The individual selection and spatial arrangement of reserve trees is determined by each timber harvest prescription and typically does not produce a uniform distribution of overstory residuals. Because of this variability, regeneration growth may be differentially affected by the level of surrounding overstory retention. In this study, I examined the development of oak species, red maple, black birch, blackgum, and sassafras regeneration under a gradient of local residual overstory basal areas in 29 mixed-oak stands for the first six growing seasons after harvest. Three measures of regeneration development were used: height growth of the tallest 10% of regeneration per sample plot, change in aggregate plot height, and average height growth of the dominant seedlings in a plot. Additional variables influencing regeneration development were included: site, initial condition of regeneration, and percentage cover of other vegetation. Linear regression models were used to determine the significance of residual basal area and other variables on species-specific regeneration development. Overstory retention had a minimal negative influence on the development of most non-oak species and was not the most important factor limiting the development of most oak species. With moderate levels of overstory retention in harvested stands, oak regeneration may benefit from their intermediate shade tolerance if suitable site and initial conditions are met. However, regeneration development of most species was most influenced by site conditions and the condition of regeneration after harvest. I also found that the growth of residual red oaks and chestnut oaks increased after harvest, suggesting that even slow growing trees respond to the release from harvest.