An examination of the relationship between stand history and composition, and American beech (Fagus grandifolia) regeneration in tolerant hardwood forests in Ontario, Canada

Within beech bark disease (BBD)-impacted stands in North America, BBD-mediated crown decline favours abundant American beech (Fagus grandifolia Ehrh.) root suckering, which can inhibit regeneration of desirable species such as sugar maple (Acer saccharum Marsh). Methods for treating beech regeneration are effective, but monetary and effort costs limit the ability to apply such treatments, resulting in the need to be able to predict beech thicket occurrence across the managed landscape. A retrospective analysis was conducted using a multivariate regression approach to identify key relationships between beech understory densities and: (1) Past management; and (2) Stand composition, in study plots (n = 1,334) within tolerant hardwood stands in the Great Lakes – St. Lawrence Forest region of Ontario, Canada. Beech sapling (p < 0.0001) and regeneration (p < 0.0001) densities were significantly higher in plots where recent logging had occurred, with the highest densities within 1-10 years following harvest. For saplings, density was also high 21-30 years post-harvest. Beech regeneration density was significantly higher among mixed composition plots where sugar maple was not the dominant canopy species (p < 0.0001). Beech sapling density, however, was higher among mixed composition plots compared to monospecific plots of sugar maple (p < 0.0001), and was not affected by sugar maple canopy dominance among mixed stands. Both sapling (rs = 0.449, p < 0.0001) and regeneration (rs = 0.600, p < 0.0001) densities were strongly correlated with beech basal area. Managers may expect to encounter abundant beech regeneration in recently disturbed, non-sugar maple-dominated stands with mixed overstory composition, while abundant beech saplings may be found in recently harvested stands with a mixed overstory composition. To limit propagation of beech in the understory, it is recommended that harvesting occur in stands where sugar maple is the leading overstory species, and beech basal area is low. Though results suggest logging disturbance increases the abundance of beech saplings and regeneration, past research has indicated that pre-logging stand composition also contributes to beech regeneration dominance post-harvest. Due to the strong monotonic relationship between beech sapling and regeneration densities and beech basal area, avoidance of harvest in stands with high beech basal area in the overstory may therefore limit beech proliferation in the understory