Shelterwood cutting to release coniferous advance growth and limit aspen sucker development in a boreal mixedwood stand

Abstract

Stratified mixtures of pioneer hardwoods sheltering shade-tolerant conifers are commonly encountered in the southern boreal forest. We used two-step shelterwood cutting to release conifer advance growth and limit trembling aspen (Populus tremuloides Michx.) development in a stratified mixed aspen–conifer stand in Quebec, Canada. This paper presents 10-year regeneration dynamics after the establishment cut applied with different cutting intensities (0%, 35%, 50%, 65%, and 100% basal area removal). Aspen suckering was proportional to cutting intensity (p<0.001) and its survival was limited under all four densities of residual cover. After 10years, aspen density was ⩽600 stems/ha in the 0%, 35%, and 50% cuts, 1600stems/ha in the 65% cut and 4700stems/ha in the clearcut. Adequate protection of balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea glauca (Moench) Voss and Picea mariana (Mill.) BSP) advance regeneration strongly contributed to limiting aspen development. The release treatment affected conifer sapling height growth, stem diameter, crown length growth and live crown ratio. Generally, the growth reaction to canopy removal was better in the clearcut than in partial cuts. Balsam fir response was good in the two initial height classes studied (130–300 and 301–500cm), but a significant spruce response occurred only in the smallest class. The final cut will be necessary to assess the overall effect of two-step shelterwood cutting on species composition and growth of the new cohort.