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Date of Award

2019

Document Type

Campus Access Master's Thesis

Degree Name

Master of Science in Applied Ecology (MS)

Administrative Home Department

School of Forest Resources and Environmental Science

Advisor 1

Christopher Webster

Committee Member 1

Christel Kern

Committee Member 2

Erik Lilleskov

Abstract

Northern hardwood forests in the Upper Great Lakes region—often existing on mesic, nutrient-rich sites and characterized by mixtures deciduous species such as sugar maple (Acer saccharum Marsh.), yellow birch (Betula alleghaniensis Britt.), and/or American beech (Fagus grandifolia L.)—have become more homogenous in composition over time due to the primary uneven-aged management system, single-tree selection (STS), which tends to favor shade-tolerant regeneration. Consequently, the proportion of trees with low shade-tolerance entering the canopy in managed northern hardwoods has decreased, while shade-tolerant species such as sugar maple have become dominant. Group-selection is an alternative form of uneven-aged management designed to naturally regenerate species within a wider range of shade-tolerances and holds promise for increasing long-term forest resilience by increasing canopy diversity. This thesis examines regeneration dynamics within two long-term group-selection experiments in Upper Great Lakes region: the Yellow Birch Legacy-Tree Project (YBLP) in the Upper Peninsula of Michigan and the Divide Canopy Gap Study (DCGS) in northeastern Wisconsin.
Chapter 2 focuses on regeneration layers (seedlings and saplings) in the YBLP. The goals were to assess regeneration composition 15 years post-harvest, the efficacy of treatments at producing more species-rich regeneration layers than adjacent STS-managed stands, and effects of opening size on regeneration composition. At 15 years post-harvest, shade-tolerant sugar maple dominated regeneration layers across all treatments with modest increases in seedling and sapling diversity within openings that may alter long-term canopy composition over several cutting cycles. We also found that gains in diversity and evenness in canopy gaps persisted through time and that large openings (22 m) had the most species-rich and even regeneration compared to reference sites.
Chapter 3 examines the composition of saplings poised to capture canopy positions within openings (termed “gap-capturing saplings”) in the YBLP and the DCGS. Tallest saplings were recorded and measured within pre-defined regions within group-selection openings at both study sites, along with pre-harvest canopy composition and post-harvest advance regeneration. Our goals were to look for compositional differences in gap-capturing saplings between opening sizes, pre-existing canopies and advance regeneration, and for spatial patterns of gap-capturing sapling composition and height within openings. Opening size did not influence overall composition of gap-capturing saplings in either study except possibly in the smallest gaps (3 m). However, site-specific factors such as harvest methods, local herbivore densities, and stand management histories appear to have greatly influenced the composition of gap-capturing saplings relative to past canopies and advance regeneration. Opening size affected sapling height but only in the smallest gaps in both studies; in the YBLP (with legacy-retention) no effect of opening size on sapling height was detected above 300–400 m2, and in the DCGS (no legacy-retention) no effect was detected above 100–200 m2. Group-selection appears to be one management option for adding shade-intolerant and midtolerant species to the overstory in hardwood forests.

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