Date of Award

Fall 12-15-2017

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forest Resources

Advisor

Laura S. Kenefic

Second Committee Member

Aaron R. Weiskittel

Third Committee Member

Jeffrey G. Benjamin

Additional Committee Members

Alison C. Dibble

Ivan J. Fernandez

Abstract

Natural disturbances of moderate severity are common in northern temperate forests in Maine, USA. Given estimated return intervals of 575-1000 years for severe windstorms and 385-1200 years for severe fire events, few opportunities arise to evaluate high severity disturbances in northern mixedwood or northern conifer forests. This research evaluated 50-year results of clearcutting with whole-tree harvesting (WTH), stem-only harvesting (SOH), and stem-only harvesting with prescribed burning (SOHB) on growing stock, composition, and relationships among foliar and soil nutrient concentrations. At the other end of the disturbance spectrum, this research also investigated 60-year results of single-tree selection with a 10-year cutting cycle (SEL). In the latter study, relationships between canopy openness and understory species diversity were quantified at different spatial scales. Both studies occurred on the Penobscot Experimental Forest, Bradley, ME.

Chapter 1 reports effects of WTH, SOH, and SOHB on growing stock and composition. Fifty years after harvest, hardwood composition was greatest in SOHB, though there were no significant differences in growing stock levels among treatments. Though present in smaller numbers, eastern white pine (Pinus strobus) was most abundant in WTH. Independent of treatment, stem density decreased with increasing O horizon thickness. Chapter 2 describes effects of WTH, SOH, and site condition on foliar and soil nutrient concentrations of dominant hardwood (red maple, Acer rubrum) and softwood (balsam fir, Abies balsamea) trees relative to an unharvested reference (REF). No effects of treatment or site were found on soil and foliar nutrient concentrations; relationships among soil and foliar nutrient concentrations were species-specific. Chapter 3 explores relationships between canopy openness and understory species diversity across varying site conditions in SEL and REF stands. Lower canopy openness was observed in SEL than REF and the effect of canopy openness on diversity varied by treatment. Below 0.12 canopy openness, understory species diversity was lower in REF than SEL; above that level diversity in REF increased with increasing canopy openness and exceeded that of SEL. Findings highlight the implications of disturbance and site for forest productivity at various spatial scales, as expressed by stand overstory stocking and composition and sub-stand understory species diversity.

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