Impact of forest liming on growth and crown vigor of sugar maple and associated hardwoods

Sugar maple (Acer saccharum Marsh.) has been declining across the unglaciated Allegheny Plateau in northwestern and north central Pennsylvania since the mid-1980s. A long-term study to evaluate the effects of fencing, herbicide, and liming on growth, crown vigor, and regeneration of sugar maple and associated Allegheny hardwoods was initiated in 1985. The study is a split-plot design with fencing (fence - no fence) as the whole-plot treatment and four subplot treatments: applications of herbicide (glyphosate) to control interfering vegetation, dolomitic lime (22.4 Mg.ha(-1)) to reduce soil acidity, dolomitic lime and herbicide, and an untreated control. Liming significantly increased diameter growth and improved crown vigor of overstory sugar maple, but did not affect growth or vigor of overstory black cherry (Prunus serotina Ehrh.) and American beech (Fagus grandifolia Ehrh.). Basal area (adjusted by covariance) of sugar maple on limed plots increased by 11% from 1986 to 1993 but only by 4% on unlimed plots. Liming increased exchangeable cations in the upper 15 cm of the soil, especially Ca and Mg, and reduced levels of exchangeable K, Al, and Mn. Changes in soil chemistry were reflected in the chemistry of overstory sugar maple foliage. Concentrations of Ca doubled on limed plots and Mg increased fourfold on limed versus unlimed plots. Liming also increased the size (in 1989 and 1992) but not the frequency of sugar maple flower and seed crops. The results demonstrate the importance of Ca and Mg nutrition in maintaining the health of sugar maple on unglaciated sites.