TEMPORAL CHANGE (1988-1990) IN SUGAR MAPLE HEALTH, AND FACTORS ASSOCIATED WITH CROWN CONDITION

Change in the health of sugar maple (Acer saccharum Marsh.) and associated northern hardwoods was evaluated for 3 years (1988-1990) in seven states and four provinces. Generally, levels of crown dieback and crown transparency (a measure of foliage density) in 165 stands decreased during this period. In 1990, less than 7% of all dominant-codominant sugar maples (n = 7317) exhibited crown dieback greater-than-or equal-to 20%. Significantly (p = 0.05) fewer of these maples were classified as having high crown transparency (greater-than-or-equal-to 30%) in 1990 compared with 1988. Crowns of maples that received moderate (31-60%) or heavy (>60%) pear thrips (Taeniothrips inconsequens (Uzel)) damage for 1 year recovered the following year. Crowns of maples exposed to severe drought in 1988 (Wisconsin) continued to show the effects (high transparency) of this stress in 1990. A majority (69-71%) of the dominant codominant sugar maples with high (greater-than-or-equal-to 20%) crown dieback had bole and (or) root damage. Of those maples with crown dieback greater-than-or-equal-to 50%, 86% had bole and (or) root damage. The condition of sugar maple in operating sugar bushes and undisturbed stands was similar. The condition of sugar maple crowns was similar in locations presumably exposed to low, medium, and high levels of sulfate deposition.