Effects of canopy opening on recruitment in Clethra alnifolia L. (Clethraceae) populations in central New Jersey wetland forests

JORDAN, R. A. AND J. M. HARTMAN (Graduate Program in Ecology and Evolution, P.O. Box 231, Cook College, Rutgers University, New Brunswick, NJ 08903). Effects of canopy opening on recruitment in Clethra alnifolia populations in central New Jersey wetland forests. Bull. Torrey Bot. Club 123: 286-294. 1996.-We measured stem growth and recruitment in three populations of Clethra alnifolia established in wetland forests, in canopy gaps, and in a recently cleared powerline right-of-way (ROW) to assess the ways in which C. alnifolia responded to canopy disturbance. Seasonal growth and density of stems and flowering rates were greater in canopy gaps, although greater overall recruitment occurred in the closed canopy forest. Total stem density, extension growth, and flowering significantly increased in the ROW and were directly related to distance from the ROW edge. Seedling density and new stem recruitment also increased significantly in the disturbed area. Clethra alnifolia demonstrated a "light flexible" response to canopy disturbance, regenerating established populations in the forest primarily through vegetative reproduction and producing greater stem density and aerial cover under disturbed canopies, but requiring significant or long-term canopy disruption to initiate increased sexual reproduction.