Regeneration dynamics following beech removal in Michigan's northern hardwood forests impacted by beech bark disease

"Beech Bark Disease (BBD) results in mortality of mature American beech (Fagus grandifolia Ehrh.) and increased beech sapling density, potentially resulting in reduced recruitment of desirable species, mast production for wildlife, and economic timber value. Changes in forest structure have been quantified in northeastern United States where BBD has been present since 1929. However, these patterns are less understood for managed forests at the western edge of beech distribution where infestations are much more recent. Furthermore, approaches aimed at ameliorating negative impacts to assure the sustainability of managed post-BBD forests are lacking. To better understand and manage BBD impacted forests, I (1) quantified regeneration structure in beech salvage harvests (partial removal) (2) assessed factors associated with regeneration patterns including winter deer use (pellet count surveys), habitat class (moisture/nutrient regime), geographic region, and post-harvest basal area, and (3) assessed the regeneration potential and likely management outcomes of study stands with a decision support tool I developed. Data used to address these goals were collected from multiple plots in 2.02 ha (5 ac) study areas in each of 69 harvested stands in northern Michigan. Throughout my study area, tree regeneration > 1.5 m tall was dominated by beech and ironwood (Ostrya virginiana (Mill.) K Koch), which are considered undesirable for management. Region (Northern Lower Peninsula vs. Eastern Upper Peninsula) was more important than habitat class (nutrient/water regime), post-harvest basal area, and current winter deer use in predicting tree regeneration composition and density. Despite dominance by undesirable species for stems > 1.5 m tall, most stands had high densities of desirable species (e.g. Acer saccharum) in < 1.5 m tall stratum. My decision support tool is based on regeneration species identity and stocking in different height stratum and the assumption that taller regeneration will "win" growing space in the near term. Applying this tool, 3% of my stands had adequate desirable regeneration, 83% of stands had undesirable regeneration in taller strata and plentiful desirable regeneration in shorter strata, potentially requiring treatments to decrease undesirable saplings and deer impacts, and 14% of stands were understocked by desirable stems in all size class and could be targeted for other treatments (e.g. conversion Pinus resinosa plantations). In conclusion, most managed stands impacted by BBD will require management aimed at regenerating more diverse and desirable mixtures of species. BBD and harvesting may affect tree regeneration patterns, but 60+ years of selection silviculture and high deer densities may also contribute."--Page ii.