Partitioning the Effect of Release and Liming on Growth of Sugar Maple and American Beech Saplings

In northeastern North America, a growing number of studies report on the regeneration failure of sugar maple (SM, Acer saccharum Marsh.) in some SM-dominated stands coupled with a marked increase in abundance of American beech (AB, Fagus grandifolia Ehrh.) in the regeneration stratum, suggesting change in forest composition toward AB dominance. The effect of release (removing all competitors within 1 m of their crown perimeters) and liming (3 Mg ha(-1) of CaCO3) on growth of SM and AB saplings was experimentally tested to partition the effect of intertree competition and soil fertility on the growth dynamics of these two species at the sapling stage. Lime application had the desired effect on soil chemistry, expressed notably as a four-fold increase in calcium concentrations of the upper soil layer (0-12 cm) and a 63% decrease in exchangeable acidity. Seven years following treatments, biomass growth response of AB saplings to release was 1.5 times higher than that of SM. In contrast, liming increased biomass growth of SM saplings (approximately 2 times compared with unlimed saplings), while there was no effect on AB growth. Also, the availability of light and of soil Ca interacts to increase growth of SM saplings. Our results confirm that SM is more sensitive to calcium availability than AB. Various forest management strategies are discussed in light of these experimental results.