Date of Award


Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)


Forest Resources


Robert G. Wagner

Second Committee Member

Aaron R. Weiskittel

Third Committee Member

Robert S. Seymour


Maines spruce-fir forest is the most commercially important forest type in the state of Maine and the Acadian Forest region. A history of natural disturbances followed by harvesting and silvicultural practices have created millions of acres of spruce-fir stands that are now ready for commercial thinning (CT). Unfortunately, there has been little research to guide development of CT prescriptions. To address this problem, I used 10-year measurements from the University of Maines Commercial Thinning Research Network (CTRN) to quantify growth & yield, residual stand structure, wood products, and financial value from factorial combinations of CT method, removal intensity, and timing of entry from two separate experiments on 12 study sites across northern Maine.

Chapter 1 examines the response of 34-70 year-old, even-aged, spruce-fir stands that had never received precommercial thinning (PCT) to a factorial combination of three CT methods (low, crown, dominant) and two intensities (33 and 50% relative density reduction), plus an unthinned control. Both intensities of the low and crown thinning produced future stands with higher quadratic mean diameter (QMD), higher sawlog to pulpwood ratio, and higher financial value per unit volume than the control and dominant thinning treatments after 10 years. The net present value (NPV) of stands following 33% low thinning was higher than all other treatments. Results indicated that older spruce-fir stands should not be commercially thinned from above due to wind losses to the residual stand. If CT is desired in older stands, low thinning to one-third relative density produced the most resilient stand structure with highest stand value and NPV.

Chapter 2 documents the response of 23-42 year-old, even-aged, fir-spruce stands that received PCT during the 1980s and 90s to a factorial combination of CT intensity (33% and 50% relative density reduction) and timing of first commercial entry (thin immediately, delay 5 years), plus an untreated control. All CT treatments improved residual stand structure and increased growth over the unthinned control. Greatest gains in QMD resulted from 50% delayed thinning, while greatest increase in net merchantable volume PAI occurred with 50% early CT. Highest financial gains occurred with 33% early CT. If the objective was to increase mean tree size and reduce the age at which trees reach a minimum size, delayed CT at higher intensity removal (50%) was best. If the objective was to increase stand value and financial returns, early CT at medium intensity (33%) was indicated.

Chapter 3 describes the effect of PCT (implemented or not), species (balsam fir, red spruce), and CT (intensity, method, timing of first entry) on changes in diameter growth, height growth, crown recession, and height: diameter ratio (HDR) of individual trees from both experiments over ten years. Trees in stands with previous PCT had lower HDR than those without PCT. Balsam fir had higher stem diameter growth than red spruce in all treatments. Crown and dominant thinning methods produced largest stem diameters, but low thinning reduced HDR more than other treatments. Early CT of higher removal intensity produced higher growth rates with less crown recession.