"Study data revealed that the benefits of liming were reduced by the relatively large amounts of sulfur deposited in forest soils as a result of many decades of acid rain," says Sharpe. "When herbicides were combined with lime and fertilizer treatments, woody seedling numbers, diversity and height growth improved significantly. Results were not as good for limed plots without herbicide treatment due to competition for growing space. But where ferns were damaged and partially eliminated by logging equipment, woody seedling growth was very good."
An increase of red maple trees in Pennsylvania forests has been noted in the last decade, occurring at the same time that northern red oaks have been decreasing in prominence, a trend that concerns many foresters. Sharpe believes his research has shown one reason why. "The red maple is a more acid-tolerant species," he says. "Residual red maple tended to grow better on the more acidic herbicide-only plots. In fact, it could be argued that the standard red oak shelterwood cut with herbicide treatment favored red maple growth."