Functional response of coniferous trees and stands to commercial thinning in eastern Canada

The overall objectives of commercial thinning are to increase individual stem growth and, arguably, to increase stand yield. Yet few empirical results are available that would confirm the treatment meets such expectations in an industrial context. We studied the response of stands to commercial thinning with a particular focus on variables that were related to processes of stemwood production at the tree and stand levels. We inventoried permanent sample plots established between 1980 and 2000 in naturally regenerated conifer stands of southern Quebec seven to ten years after thinning. We reconstituted tree leaf area and wood production per unit leaf area using field and dendrochronological data for different years following thinning. Mixed linear models showed that tree basal area and leaf area increments following treatment were strongly related to the tree distance from the nearest skid trail. Wood production per unit leaf area was significantly higher for trees located within 5 m of a skid trail compared to control trees as soon as one year following thinning application, while significant differences in tree leaf area required five years. Compared to control stands, thinned stands had higher wood production per unit leaf area, but merchantable volume increment did not differ. These results provided insight into growth processes that are involved in tree responses to mechanized thinning and could aid in the development of decision tools that determine the suitability of stands for receiving the treatment.