Improving the Composition of Beech-Dominated Northern Hardwood Understories in Northern Maine

regeneration and pole-sized beech densities (Jones et al. 1989, Bohn and Nyland 2003, Nolet et al. 2008), but with larger gap/patch openings, beech densities can be reduced while allowing shade-tolerant sugar maple to grow beneath shade-intolerant species that establish after harvest (Leak 1999). Subsequent timber stand improvement can then be used to shift species compositions to sugar maple and yellow birch (Leak and Smith 1997). Shelterwood harvests can favor beech-dominated understories when residual beech regeneration remains, root suckering increases, and harvests occur on mid-quality sites, because beech is typically more competitive than sugar maple on sites low in calcium and nitrogen (Boerner and Koslowsky 1989, Long et al. 1997). Preharvest site preparation (Kelty and Nyland 1981) and postharvest herbicide applications (Ostrofsky and McCormack 1986) can be effective strategies for promoting the establishment of sugar maple and yellow birch when combined with even-aged management. Advances in forest herbicide technology, including precise application rates, make it possible to test the performance of treatments designed to release desirable hardwood species from understory beech cover, similar to northern conifer release treatments (sensu Newton et al. 1992, Wagner and Robinson 2006). The high susceptibility of beech and low susceptibility of sugar maple to moderate glyphosate rates (Ostrofsky and McCormack 1986, Pitt et al. 1992, 1993) makes this herbicide an ideal candidate for testing the selective removal of beech and preservation of sugar maple following shelterwood harvests. We hypothesized that by systematically adjusting the glyphosate rate and surfactant concentration that a treatment combination could be identified that produced maximum beech control and minimal injury to sugar maple and other desirable hardwood species. The objectives of this study were to (1) document the relative susceptibility of five major hardwood species in Maine northern hardwood stands (beech, sugar maple, red maple, striped maple, and yellow birch) to various combinations of glyphosate herbicide (Accord Concentrate) and surfactant (EnTree 5735); (2) identify an optimal combination of glyphosate rate and surfactant concentration that produced the highest level of beech control and lowest level of sugar maple injury; and (3) determine whether the results produced using hydraulic nozzle applications (which were required to precisely control herbicide and surfactant application rates) were transferable to mistblower applications that would typically be used for industrial herbicide applications.