THE RELATIONSHIPS OF CROWN DIEBACK WITH CARBOHYDRATE CONTENT AND GROWTH OF SUGAR MAPLE (ACER-SACCHARUM)

Since the early 1980s, some sugar maple (Acer saccharum Marsh.) forests in northeastern North America have shown severe signs of dieback and decline. This study was designed to determine the relationships of crown dieback of sugar maple with carbohydrate content for different tissues during fall and spring and with radial growth patterns. A 100-year-old sugar maple stand located in Tingwick (Quebec, Canada) was sampled in 1987 and 1988. Growth, starch, and water-soluble carbohydrates (sucrose, glucose, and fructose) were measured in relation to crown dieback for 55 sugar maple trees. Root and stem samples were collected in April (1988), during the bud burst period, and in October (1987 and 1988), just after leaf drop. Starch was the predominant carbohydrate. In April, stem samples contained higher concentrations of glucose and fructose than in October. Conversely, roots had higher concentrations of reducing sugars in October, especially in trees, that were heavily affected by dieback. Roots of such trees also contained lower starch concentrations in October than in April. A crown deterioration index emphasized the increase in reducing-sugar concentrations found in autumn in roots of the deteriorating trees. Basal-area increment at 1.4 m was assessed from ring widths of cores collected from the trees under study. A significant growth decrease was observed for trees with 25% or more crown dieback, particularly for the last 5-year period. Thus carbohydrate concentrations and growth measurements prove to be valuable parameters in assessing tree health. Moreover, it seems that the physiological imbalances observed in declining trees may decrease the resistance of sugar maple against biotic and abiotic stresses.