© 1990 Heron Publishing—Victoria, Canada
Interactive effects of resource availabilities and defoliation on photosynthesis, growth, and mortality of red oak seedlings
James B. McGraw (1), Kurt W. Gottschalk (2), Milan C. Vavrek (1) and A. L. Chester (1)
1. Department of Biology, West Virginia University, Morgantown, WV 26506-6057, USA / 2. USDA Forest Service, Northeastern Forest Experiment Station, P.O. Box 4360, Morgantown, WV 26505, USA /
Summary
Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to site and from individual
to individual. To determine whether some of this variation could be explained by variation in other stress factors, red oak
(Quercus rubra L.) seedlings were exposed to low and high light, water, mineral nutrient, and defoliation treatments, in a complete factorial
design in a greenhouse. Significant interactions were observed among factors for photosynthesis, growth, and mortality, indicating
that the response to defoliation was influenced by other stresses. Defoliation increased the photosynthetic capacity per unit
leaf area of seedlings grown in the low-water, but not in the high-water, regime. In response to defoliation, growth of seedlings
in a low-mineral-nutrient, or low-light, regime was depressed less than that of seedlings grown in a high-mineral-nutrient,
or high-light, regime. However, defoliation resulted in a similar percent reduction in biomass in all seedlings in both the
high and the low light, water, and mineral nutrient treatments. Defoliation-induced mortality of shaded plants was twice that
of plants grown in full sun.
