The tree-ring chemistry of declining sugar maple in central Ontario, Canada

Tree-ring size and chemistry of healthy and declining sugar maple (Acer sac charum Marsh.) trees, growing in nutrient-poor soils derived from the Preca mbrian Shield in Ontario, were used to document historical changes in tree nutrition since the mid-1940s. At Dorset, a site showing extensive decline symptoms which have been observed annually since 1986, a reduction in tree- ring width occurred in rings formed during the 1940s, although after 1950, tree-ring size and concentrations of Ca, Mg and Mn have been constant. Conc entrations of Ca (680 mg kg(-1)) and Mg (100 mg kg(-1)), however, are among the lowest recorded in sugar-maple wood. At Loring, a site which appears m uch healthier than Dorset, a reduction in tree-ring width occurred during t he 1960s, 20 years later than at Dorset, and was accompanied by substantial reductions in concentrations of Ca and Mg, and in particular Mn. Trace met al or Al toxicity are unlikely to be directly responsible for the decline s ymptoms. If Loring is representative of healthy looking sugar-maple forests in central Ontario, more extensive visual decline symptoms arising from nu trient deficiencies may occur during the next 20 years.