Factors associated with the decline disease of sugar maple on the Allegheny Plateau

Mortality of sugar maple (Acer saccharum Marsh.) has reached unusually high levels across northern Pennsylvania since the early to mid-1980s. We evalu ated the influence of glaciation, topographic position, foliage chemistry, defoliation history, and stand characteristics (species composition, struct ure, density) on the health of sugar maple in 43 stands at 19 sites on the northern Allegheny Plateau. Using percent dead sugar maple basal area as th e measure of health, we found that all moderately to severely declining sta nds were on unglaciated summits, shoulders, or upper backslopes. Stands on glaciated sites and unglaciated lower topographic positions were not declin ing. The most important factors associated with sugar maple health were fol iar levels of Mg and Mn and defoliation history. The lowest foliar Mg, high est foliar Mn, and highest number and severity of insect defoliations were associated with unglaciated summits, shoulders, and upper backslopes. Decli ning stands had less than 700 mg,kg(1) Mg and two or more moderate to sever e defoliations in the past 10 years; both conditions were associated with m oderately to severely declining stands. The decline disease of sugar maple seems to result from an interaction between Mg (and perhaps Mn) nutrition a nd stress caused by defoliation.