Directional Variation in Growth of Trees

Abstract

Asymmetrical differences in root systems and crowns were investigated at the Morton Arboretum, N. Illinois. Crown radii (N. and S.), annual branch length and dry weight increment, and leaf area were measured in 1988 and 1989 for 36 broadleaf species approximately 30-years-old. Root densities for 4 littleleaf linden ( Tilia cordata cv. Greenspire) trees were determined in 1987 along N. and S. transects, at 0.6-m intervals, up to 7.2 m from the bole. For crown measurements in 31 species, north side radii were greater than south side radii; in 8 species this difference was significant. Twig growth and dry weight were greater on the north side. Fine root density was greater on the north side, but not significantly. Possible reasons for the growth differences (soil moisture, effects of canopy shade, water stress, direct sunlight) are discussed.