Widespread paper birch (Betulapapyrifera Marsh.) mortality associated with the activity of the bronze birch borer (Agrilusanxius Gory) was observed across northern Michigan in 1991. This mortality occurred at two study sites on which paper birch growth has been intensively monitored since 1985. Recent warmer than normal growing seasons and lower than normal moisture availability are statistically associated with a reduction in annual diameter growth. On one study site 62% of the paper birch study trees were dead and 13% were visibly declining; on the other study site, although no trees were dead, 25% of the paper birch study trees were visibly declining. Growth reductions since 1985 suggest that the species was under climatic stress, making it more vulnerable to pest–pathogen activity. The evidence of the role of climatic conditions acting as a precursor to decline and mortality on these sites is of serious concern given recent projections of warmer temperatures and lower precipitation for this region by several global-climate models.

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A gradient of H +, SOng and NO~ deposition across the Great Lakes region raised concerns over impacts on soil solution chemistry and ion leaching in regional forest ecosystems. Ten study sites representing northern hardwood and oak ecosystems were established across the gradient of increasing deposition from Minnesota to Ohio. Lysimeters were installed at lower E and lower B horizon boundaries at each site and sampled over a 2-yr period. In soil solutions collected at lower E horizon boundaries, H ÷ and SO~-wet deposition were correlated with solution concentrations of SO~-r = 0.82** and 0.92**) and Mg 2+ (r = 0.75** and 0.85"*), and with the SO~-/inorganic anion ratio (r 0.71"* and 0.70**). In soil solutions collected at lower B horizon boundaries, SO~-deposition was correlated with solution SO~-concentrations (r = 0.92**). Greater ionic outputs from B horizons than atmospheric inputs indicated that net losses of Ca 2+ and Mg 2+ were occurring from all sites. Sulfate outputs above background levels contributed 33 to 2367 molc SO~4-ha-~ yr-~ from north to south along the gradient, equal to 3.7 to 71.7% of annual cation outputs. Excess H + deposition accounted for 8 to 34% of annual cation outputs from north to south, and as much as 72% at one site with coarse-textured soils. Elevated cation losses related to H + and SO4deposition indicate that cation depletion remains a plausible consequence of pollutant deposition to forest ecosystems with poorly buffered soils. A TMOSPHERIC POLLUTANT DEPOSITION has been a focal issue in forest ecosystem research for the past 20 yr. Much effort has centered on determining the extent to which elevated pollutant (H ÷, SO2-, NO ~) deposition results in increased leaching of cations from forest ecosystems (e.g., Johnson et al., 1983; Binkley and Richter, 1987; Johnson and Taylor, 1989). Many site-specific studies of the effects of atmospheric deposition on soil solution chemistry and ion leaching in forest ecosystems have been conducted (e.g., Mollitor and Raynal, 1982; Foster, 1985; Johnson and Todd, 1990). Few previous studies have examined the effects of pollutant deposition on soil solution chemistry and ion leaching in forest ecosystems at multiple sites located across regional gradients of air pollutant deposition. A pronounced gradient of atmospheric pollutant deposition exists across the Great Lakes region (Armentano and Loucks, 1983; Schwartz, 1989; Mac-Donald et al., 1991a). Annual wet SO~-S deposition increases from less than 3.5 kg ha-1 in northern Min

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