The role of silvicultural thinning in eastern forests threatened by hemlock woolly adelgid (Adelges tsugae).
In order to increase hemlock (Tsuga sp.) survivability in stands threatened by hemlock woolly adelgid (HWA, Adelges tsugae), a new study is developing silvicultural thinning guidelines to reduce stand densities, reallocate resources, and increase hemlock vigour across a range of stand types and structures before HWA invasion. The 7 study areas are all geographically similar in that they regularly experience winter temperatures that can be lethal to hemlock woolly adelgid. The combined effects of climate and silvicultural treatment may serve to moderate adelgid populations and increase hemlock survival. Four Pennsylvania stands received thinnings in 2006 to reduce relative stand density by 30-40%. Half of each stand was not harvested and serve as controls. In New England, four additional sites are being thinned from 2007 2008. Pre- and post-harvest sampling includes measurements of stand density and structure, residual 'crop' tree stems and crowns; understorey vegetation; soil moisture, temperature and nutrients; foliar nutrients; and insect populations.