In this study we compare the mechanical resistance of black spruce (Picea mariana (Mill.) BSP) and jack pine (Pinus banksiana Lamb.) and quantify the effect of species, forest cover type, and soil conditions on tree stability. To measure tree resistance to an applied load, 85 trees were pulled over using a cable and winch system. Predictive equations for the maximum turning moment that a tree can withstand (Mc) were developed with stem mass, and the other factors were used as explanatory variables. The presence of jack pine within the stand negatively affected black spruce resistance. In mixed stands, Mc was significantly influenced by the interaction between tree species and soil type. Jack pine was the only species with significantly lower resistance when grown on shallow and stony soils, which are likely to restrict root development. Black spruce resistance was not affected by soil conditions. Preliminary calculations of critical wind speeds required to cause damage using an adaptation of the ForestGALES model were much lower than those previously published for black spruce.

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RÉSUMÉUn total de 48 placettes issues de coupe totale localisées dans le domaine bioclimatique de la sapinière à bouleau jaune de la province de Québec, Canada, ont été étudiées au moyen d'une analyse dendrochronologique afin d'évaluer l'importance de la composition avant coupe, de l'abondance et de la structure de la régénération après coupe et du type de milieu physique sur la dynamique des peuplements. Les résultats démontrent le lien entre le couvert d'origine et les peuplements de retour. La considération des conditions écologiques apparaît indispensable pour caractériser l'importance de la régénération préétablie et pour décrire l'évolution des coefficients de distribution. Les résultats permettent également de mettre en lumière la pertinence de considérer la structure de la régénération, par le biais de l'indice de diamètre, pour prédire le rendement à 38 ans. Les dommages causés par la tordeuse des bourgeons de l'épinette constituent un facteur déterminant dans l'évolution des peuplements dans le cadre de cette étude et rendent difficile la prédiction du rendement des peuplements régénérés en sapin. Enfin, les résultats mettent en évidence le phénomène d'augmentation des feuillus intolérants à l'ombre et les problèmes de productivité résineuse sur stations riches. La pessières noires se reconstituaient en peuplements de même composition. Mots-clés : peuplements mixtes, succession, inventaires de régénération, rendement, Choristoneura fumiferana ABSTRACTA total of 48 plots originating from clearcuts were studied in the balsam fir-yellow birch ecological domain of the province of Quebec, Canada, using dendrochronology. The aim of the study was to assess the effect of pre-cut stand type, structure and abundance of regeneration after logging, and soil type on stand dynamics. Results indicate a relationship between pre-cut stand type and the composition of second-growth stands. Ecological characteristics must be taken into account in order to estimate the abundance of advance regeneration and predict the evolution of stocking. Results also show that the structure of regeneration, described by a diameter index, can help in predicting yield at age 38. Devastation by the spruce budworm played a major role in second-growth stand dynamics making it difficult to predict balsam fir yield. The study has also shown an increase in intolerant hardwoods and a low softwood production on rich sites. Black spruce stands came back to black spruce.

Many hardwood or mixedwood stands of northeastern North America have been high graded in the past and need restoration treatments to bring them back to an acceptable level of production. Even when early seedling establishment can be secured, further development may be compromised bymany factors. This study looks at the effect of seedbed, browsing, and competition on the growth and survival of yellow birch (Betula alleghaniensis Britt.) seedlings that became established after a brushing and scarification treatment applied in high-graded mixedwood stands of Quebec,Canada. The seedbed types studied include 1-m-wide scarified patches, 2-m-wide scarified patches, and mounds. Browsing impact was assessed by placing fences around half of the plots. Half of the plots were released from competing vegetation. Browsing by hare (Lepus americanus) was seenas a major factor controlling seedling development between 3 and 6 years after scarification. It reduced both survival and growth and obscured the effect of other factors. In the absence of browsing, competition had a major effect on mounds but not on scarified patches. Mounds were found tohave the best growth potential when competition and browsing were controlled. The scarified patches had the best growth when competition and browsing were allowed. Even though mortality was somewhat higher on scarified patches, initial densities were very high and still provide more seedlingsthan required.