Directional Variation in Growth of Trees

A previous study on the root distribution of seven species of shade trees revealed asymmetric root systems (6).The north and west sides of the trees had the largest number of roots greater than 1.0 cm in diameter.No assessment of fine root development was reported.Since the trees used in the study were growing in nursery blocks with a completely closed canopy, the soil environment was consistent on all sides and probably not a factor in the differential root development.Above-ground factors such as light intensity and drought stress were implicated.Asymmetrical differences in the root systems and crowns of trees need to be more fully understood because of the possible relationship to everyday practices, such as watering, in the arboriculture and nursery industries.