Northern hardwood forests (NHF) of the upper Great Lakes region have undergone a century of structural simplification and compositional homogenization due to exploitative logging of old-growth stands and the ubiquitous application of selection silviculture in second-growth stands. Contemporary partial harvests often fail to regenerate well-stocked, species-diverse regeneration layers, a pattern attributed to low light availability and deer browsing, among many other limiting factors. This dissertation investigates silvicultural strategies for promoting well-stocked, diverse tree regeneration in managed NHF of northern Michigan, USA, as these conditions are likely to strengthen NHF resilience to future disturbances.Chapter 2 examines six-year diversity and stocking outcomes following a harvest intensity gradient representing four silvicultural systems: single-tree/small group selection, shelterwood, large group selection, and seed tree. Across 72 stands, species diversity and stocking of a species group desirable for biomass productivity objectives increased with harvest intensity, mainly through the addition of shade-intolerant species. However, a group of largely shade-tolerant and midtolerant species desired for NHF wood economics objectives was less responsive to harvest intensity. Stocking of these groups also exhibited marked regional variation, suggesting that harvest intensity alone does not fully determine early regeneration outcomes. In Chapter 3, individual species analyses revealed stocking of shade-intolerant species was associated with increased harvest intensity, whereas shade-tolerant and midtolerant species were best predicted by advance regeneration and pre-harvest canopy tree density, suggesting pre-harvest stand structure is critical for many important NHF species. As browsing pressure increased, some browsing-preferred species exhibited slightly reduced stocking, while stocking of prominent browsing-resilient or avoided species increased modestly; deer browsing likely exerts its greatest influence on regeneration outcomes by shaping the structure and composition of advance regeneration in the decades preceding harvest, rather than in the years that follow. Given the importance of advance regeneration for many NHF species, Chapter 4 examines regeneration dynamics by relating sugar maple (Acer saccharum) seedling density to the diameter and density of local seed sources. Seedling counts were most strongly predicted by the density of sugar maple stems > 40 cm dbh within 35 – 40 m. Applying this relationship to a state resource-wide dataset of 126 managed NHF stands revealed that many stands lack sufficient densities of these large-diameter seed sources, which could constrain the establishment of dense advance regeneration layers, suggesting a need to revise residual stand targets. Chapter 5 investigates direct seeding as a method to augment regeneration diversity. Ten native or assisted migration candidate species were sown across a gradient of harvest intensity in plots that were either accessible or inaccessible to seed predators. Establishment was highest for large-seeded species that were buried, and was not influenced by harvest intensity. In contrast, small-seeded, broadcast-sown species exhibited lower and more variable establishment, especially following high-intensity harvests. Although seed predation reduced establishment across all treatments, it was not severe in most stands, suggesting that direct seeding may be a viable strategy for increasing diversity in NHF regeneration layers. Together, these findings suggest that silvicultural practices such as increased harvest intensity, large-diameter seed source retention, and artificial regeneration practices such as direct seeding are likely to foster more diverse and resilient regeneration layers in managed northern hardwood forests of the upper Great Lakes region.
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