Probabilites de pertes des tiges individuelles, cinq ans apres des coupes avec protection des petites tiges marchandes, dans des forets resineuses du Quebec

Harvesting with protection of small merchantable stems is a type of partial harvesting whereby all trees larger than 15.0 cm in diameter at breast height (dbh) are usually cut while smaller stems are retained. In mature coniferous stands dominated by balsam fir (Abies balsamea (L.) Mill.) or black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.), the success of the treatment depends partly on the survival of retained trees. A mixed logistic model was calibrated to identify the variables affecting the likelihood of losses of protected individual stems with dbh >= 5.1 cm, by standing-tree mortality or windfall, 5 years after harvesting with protection of small merchantable stems in 27 experimental cutblocks in Quebec. The results indicate that postharvest losses were largely dependent on preharvest stand characteristics (merchantable basal area, sapling density, and jack-pine (Pinus banksiana Lamb.) ratio), the quality of the treatment (harvesting methods, retention rate of small merchantable stems), and the characteristics of retained trees at harvest time (tilt, dbh, and species). The variables associated with wind exposure and site ecology did not allow for improvement of the model. It is imperative to carefully choose the stands to be treated and to closely monitor harvesting to minimize losses.