Initial tree regeneration response to natural-disturbance-based silviculture in second-growth northern hardwood forests

Northern hardwood stands in the Great Lakes region are often managed using single-tree selection, which generally favors regeneration of shade-tolerant species, especially sugar maple (Acer saccharum Marsh.) and may reduce regeneration of midtolerant and shade-intolerant species. These forests also tend to have lower microsite diversity than old-growth stands, which may negatively affect the regeneration of light-seeded species, including yellow birch (Betula alleghaniensis Britton). The objective of this research was to determine the initial effects of gap size and gap cleaning on tree regeneration in northern hardwood stands in northern Wisconsin, USA. The current study evaluated three gap sizes compared with a control. A gap-level cleaning treatment also examined effects of removal of advance regeneration and soil scarification. Postharvest seedling densities, especially shade-tolerant species, increased with increasing gap size. Rubus spp. increased significantly in the higher light conditions in these treatments. Density of yellow birch seedlings and saplings was low for all gap sizes but increased with removal of advance regeneration and soil scarification. These initial results underscore the challenges of using natural-disturbance-based treatments to increase the diversity of tree communities in second-growth forests and the importance of advance regeneration and seedbed conditions for increasing the abundance of historically important species.