Compression wood and stem horizontal displacement in black spruce and Jack pine plantations in the boreal forest

• Evaluation of stem horizontal displacement in conifer plantations in the boreal forest.
• Occurrences of compression wood along the stem.
• Relationships between stem horizontal displacement and dendrometric data.
• Fast growth of Jack pine explains the highest proportion of compression wood.

Black spruce and Jack pine are the tree species most often planted in the boreal forest of the province of Quebec. Higher radial growth is expected from these stands in comparison with naturally regenerated forests. The fast growth response of these tree species in plantation has been associated with stem displacement and compression wood formation. This study aims to examine these parameters and to relate them with dendrometric variables. Analysis were conducted in 10 black spruce and 10 Jack pine plantations over 20 years old. Stem horizontal displacement was evaluated at stand level within plots of at least 50 stems. A sub-dataset of five dominant trees per plantation was then sampled in order to quantify the occurrences of compression wood. Stem horizontal displacement was mostly sparse for black spruce. In agreement with this observation, compression wood ratio (0.6% of total tree volume) can be considered low for this species. For Jack pine, the measurements of compression wood (5.0% of total tree volume) were higher than black spruce. Compression wood ratio was negatively correlated to stem height and positively to maximum stem horizontal displacement and tree crown cover ratio. We think that the capacity of Jack pine to grow faster, in given conditions, than black spruce is the main reason for the higher occurrence of sinuosity and compression wood in Jack pine plantations.