Shelterwood cutting in a boreal mixedwood stand: 5-year effects of the final cut on development of aspen suckers and released conifers

Abstract

We used the two-step shelterwood cutting to release conifer advance growth and limit the development of trembling aspen (Populus tremuloides) suckers in a stratified mixed aspen – conifer stand. This study presents the effects of the final cut, applied 12 years after the establishment cut, on the 5-year response of advance regeneration and aspen sucker development. Suckering was inversely proportional to the intensity of the establishment cut, with 19 000, 14 900 and 6800 stems/ha two years after the final cut, respectively, in the initial removal of 35%, 50% and 65% basal area. By year 5 however, the treatment effect on stem density was no longer significant due to high aspen mortality in the 35% and 50% cuts. At this time, the density of conifer stems taller than 100 cm was comparable to that of aspen stems in the 35% and 50% cuts, while conifers dominated the 65% cut. Standing mortality was higher for hardwood (22–28%) than for conifer (4–9%) advance growth, except in the uncut control (14% and 9%, respectively), while windthrow averaged 4% and 8%, respectively, in the three partial cuts without being related to treatment. Small merchantable conifer stems (diameter at breast height – DBH 9.1–15.0 cm) that were retained were most affected by windthrow, but overall losses were found acceptable considering DBH and height growth of the surviving stems. This study confirms that the two-step shelterwood cutting that secures conifer advance regeneration should be considered to limit hardwood conversion in the boreal mixedwood forest.