The Ontario Hardwood Forest Health Survey: 1986 – 1998

In 1986 the Ontario government established a long-term program to monitor hardwood forest health. The program was initiated in response to widespread reports of forest decline in North America and Europe and the implication that air pollution, specifically acidic deposition, was a causal factor. Visual symptoms of branch dieback, leaf colour, and leaf size, have been quantitatively evaluated on about 15 000 trees in 110 plots. This report summarizes the results of the first 12 years (1986 to 1998). Over that time period, relative to the 1986 baseline year, 84% of the plots have improved in condition, 12% have not changed, and 4% have deteriorated. Generally, hardwood forest health in the province appears to be quite good; severe decline is limited and very site-specific, occurring only in selected northern regions on acid-sensitive and/or marginal sites, or in southern areas on very shallow soils. Northern forests growing on coarse-textured shallow soils underlain by precambrian rock are in poorer health relative to southern forests growing on finer-textured, deeper soil over limestone. On soils sensitive to acidic deposition, tree health deteriorated as soil pH and exchangeable aluminum levels increased. Key words: forest health, forest decline, decline index, Ontario, hardwood, air pollution, acid rain