Long-term black spruce plantation growth and structure after release and juvenile cleaning: A 24-year study

Abstract

Vegetation management is crucial to meet growth and yield objectives in conifer plantations. But, the combined and longterm effects of mechanical release and juvenile cleaning on growth and stand structure have yet to be documented in black spruce plantations. A long-term study was carried out in Quebec (Canada) to evaluate the interactions between initial mechanical release at age 2 years and juvenile cleaning at age 14 years (i.e., a second release treatment) on planted black spruce survival and dimensions at age 24 years. Population structure and stand species composition were also assessed. Results showed that release and juvenile cleaning had an additive, positive effect on survival, diameter at breast height (DBH), height, crown width, crown length, and the last 5-year DBH and height increments. Juvenile cleaning effects were of higher magnitude than release effects, especially on 5-year DBH increment. Combination of both treatments reduced DBH and height variability of saplings, whereas juvenile cleaning alone resulted in a higher proportion of saplings occupying higher height classes. Total merchantable basal area was constant among treatments. But, without juvenile cleaning, hardwoods occupied a higher proportion of the basal area and were taller than spruces. In a context of sustainable forest management, in which conifer plantations are expected to offer high wood yield, our results demonstrate the importance of juvenile cleaning following initial mechanical release to promote crop tree growth and yield. Key words: plantation, vegetation management, black spruce, growth, stand development