Chronology of growth in balsam fir seeds, Abies balsamea (L.) Mill., after clearcutting with regeneration protection

The method of harvesting with protection of the advanced regeneration consist,, of a complete removal of the main canopy to release a seedling bank established under the overstory shade. After harvesting, seedlings acclimated to understory conditions could suffer from moisture stress, especially the small, juvenile seedlings (less than six years), The objective of the study is to determine the capacity of understory-acclimated balsam fir seedlings to respond positively and immediately to release, The response to release was studied in two seedling populations belonging to two distinct climatic regions of Quebec, the Western and the Eastern sections of the balsam fir-white birch ecological domain. Results show that the response patterns were similar in both populations. Response to release occurred in two steps, One year after harvesting, basal ring width was on the average times larger than prior to harvesting (p >0.001). Height growth only became significantly higher the second year after release (p < 0.001). On average juveniles showed higher height growth rates (height growth/height) than older seedlings. This rate was negatively correlated to seedling, height at harvesting (r= -0,68, p < 0.001). Our study clearly shows that balsam fir seedlings can respond immediately and positively to large openings. The strong response of juvenile seedlings to release indicates that these can contribute significantly to the future stand. The geographic and climatic differences between the two stands under study suggest that these observations apply to a wide range of balsam fir stands.