Date of Award

2015

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Forest Science (PhD)

Administrative Home Department

School of Forest Resources and Environmental Science

Advisor 1

Robert E. Froese

Advisor 2

Linda M. Nagel

Committee Member 1

Evan S. Kane

Committee Member 2

Gary A. Campbell

Abstract

Commercial aspen (Populus spp.) forests of the Great Lakes region are primarily managed for timber products such as pulp fiber and panel board, but logging residues (topwood and non-merchantable bolewood) are potentially important for utilization in the bioenergy market. In some regions, pulp and paper mills already utilize residues as fuel in combustion for heat and electricity, and progressive energy policies will likely cause an increase in biomass feedstock demand. The effects of removing residues, which have a comparatively high concentration of macronutrients, is poorly understood when evaluating long-term site productivity, future timber yields, plant diversity, stand dynamics, and consequently, appropriate silviculture.

These practices were evaluated throughout the western Upper Peninsula of Michigan using forest inventory data from harvested stands over the last 45 years. Assessment provided a framework of ecosystem carbon patterns across stand rotation, and comparisons reflected moderate losses in residue-bound carbon pools when captured. However, residue loads exceeded those recommended by established residue retention guidelines even in stands where residues were recovered for bioenergy. Soil nutrient pools exhibited declines under residue removal treatments on coarse textured soils. Aboveground biomass and timber yields did not vary according to residue treatment, and development of the aspen cohort was similar across all soil types, regardless of nutrient levels, an unexpected result. Stand dynamics varied by soil productivity class in the late stages of stand rotation, and imply that encouragement of non-crop trees for ecological purposes does not affect yields of the aspen resource. Predictions based upon historical growth and yield models showed mixed levels of accuracy when compared to observations. Analyses of vegetation communities and multivariate ordination methods revealed temporal patterns in species richness and increased heterogeneity under residue removal treatments. A spatially explicit sampling design was utilized to examine advances in harvesting technology on variance in stand level regeneration, soil nutrients, and residue estimates. Operator and equipment induced patterns in harvesting activity were found to increase residue loads with a concomitant decline in stem density and height growth across a large portion of the regenerating stand.

Collectively, these findings suggest that residue removal results in a minor decline in aboveground C stocks, and coarse textured soils may be susceptible to reductions in forest soil nutrient pools. Further, variations in growing conditions at the forest floor due to high residue loads may adversely affect understory vegetation communities. Finally, harvesting equipment, cut-block layout, and residue distribution can influence stand regeneration patterns, and warrants consideration in harvest and silvicultural planning.

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