Graduation Year


Graduation Month


Document Type


Degree Name

Bachelor of Science – Forestry

School or Department

Forestry and Conservation, College of



Faculty Mentor

Andrew J. Larson

Faculty Mentor Department

Forestry and Conservation, College of


forestry, restoration, silviculture, forest ecology, conifer encroachment, wildlife

Subject Categories

Forest Biology | Forest Management | Forest Sciences


Many quaking aspen (Populus tremuloides) populations are in decline across the western United States, a trend likely driven by ongoing climate change and past management that has led to increased competition with conifers. Restoration of aspen is a management goal potentially achievable through active forest management, but treatment effects on regeneration and residual growth have not been comprehensively studied. This project examined if removal of competing conifers altered aspen regeneration density, ungulate browsing, and residual adult aspen diameter growth using a control-impact study design. Sampling occurred at the Burnt Fork (ten treatments, four controls) and Bandy (seven treatments, four controls) sites. Nested plot-centric circles with a common center point were used for sampling. Regeneration was counted in 0.004-hectare plots and examined for ungulate browsing. Adult trees were surveyed in 0.04-hectare plots; diameters and increment cores were taken on the most vigorous tree to represent growth before and after harvest. Ungulate browsing (percent of regeneration browsed) means were higher in treated units (23% and 46% browsed at the Burnt Fork and Bandy, respectively) than in control units (3% and 2% browsed at Burnt Fork and Bandy, respectively). Aspen regeneration was higher in treated units than controls: regeneration at the Burnt Fork site averaged 10743 stems/ha in treated units and 7054 stems/ha in controls, while the Bandy site averaged 13438 stems/ha in the treated units and 6824 stems/ha in controls. Average adult aspen diameter growth rates were stable or increased from pre- to post-treatment in treated units, while diameter growth rates were stable or decreased from pre- to post-treatment in controls. This study demonstrates that silvicultural treatments to remove competing conifer trees can increase aspen regeneration density and maintain or increase adult aspen growth rates. Managers seeking to regenerate declining aspen stands can use conifer removal treatments to promote aspen regeneration.

Honors College Research Project




© Copyright 2016 Philip W. Williams