INFLUENCES OF LIGHT-INTENSITY ON WEED-INDUCED STRESSES OF TREE SEEDLINGS

Growth of northern red oak Quercus rubra, white ash Fraxinus americana and white pine Pinus strobus seedlings was evaluated after germination in environments that consisted of 4 levels of herbaceous interference (fern, fern free, grass, grass free) crossed with 3 levels of light intensity (100, 45, and 20% full sun), in C Pennsylvania. Grass and fern interference reduced soil moisture content and reduced height or diameter growth of all species. Shading ameliorated soil moisture, reduced herbaceous growth, generally reduced growth of all tree species in interference-free environments, and had no effect on growth of any tree species in fern and grass environments. Reduction in growth due to herbaceous interference was lower for northern red oak and white pine; shading had similar effects on growth of all species. Stresses induced by shading alone have little short-term effect on the establishment of these species under conditions of heavy herbaceous interference. -from Authors