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Survival and growth of planted white spruce (Picea glauca (Moench) Voss) were assessed at year 15 in boreal mixedwood stands of northern Alberta, Canada, in stands that were deciduous-dominated prior to logging or were conifer-dominated. Three overstory retention levels (0%, 50%, and 75% retention) and four site preparation treatments (mound, high speed mix, scalp, and no treatment) were evaluated. In deciduous-dominated stands, planted spruce performed best in the 50% retention; here, stem volume was at least double that of any other retention treatment after 15 years. In contrast, spruce had reduced growth in coniferous-dominated stands in both 50% and 75% retention treatments compared with the 0% retention. Survival of planted spruce was unaffected by level of retention, but survival was lower in coniferous-dominated stands than in deciduous- dominated stands; in the coniferous-dominated stands, survival was better with mounding and mixing and lowest with scalp treatments. All height variables tended to be greater in the mix and mound site preparation treatments. Finally, the best estimates of future total growth (regenerated spruce and deciduous combined) in the coniferous-dominated stands were in the clearcut treatment. In terms of regenerated spruce growth, the best estimates occurred in the deciduous-dominated - 50% retention stand planted with soil mixing-mounding treatments, where projected growth of spruce was comparable with that of open-grown and tended stands in Alberta's boreal forests. Key words: boreal mixedwood, shelterwood, site preparation, survival, partial harvest, planted, variable retention, white spruce. La survie et la croissance de plants d'epinette blanche (Picea glauca (Moench) Voss) ont ete evaluees a l'age de 15 ans dans des peuplements mixtes boreaux du nord de l'Alberta, au Canada, sur des stations dominees avant la coupe par des feuillus ou par des coniferes. Nous avons evalue trois niveaux de retention du couvert dominant (0, 50 et 75 % de retention) et quatre traitements de preparation de terrain (monticules, melange du sol agrande vitesse, scalpage et temoin non traite). Dans les peuplements domines par des feuillus, les plants d'epinette croissaient mieux a 50 % de retention du couvert dominant. Dans ce cas, le volume des tiges etait au moins le double de celui observe dans les autres traitements de retention apres 15 ans. En revanche, une croissance reduite de l'epinette a ete observee dans les peuplements domines par des coniferes avec 50 et 75 % de retention comparativement a 0 % de retention. La survie des plants d'epinette n'a pas ete influencee par le niveau de retention, mais elle etait plus faible dans les peuplements domines par des coniferes que dans ceux domines par des feuillus. Dans les peuplements domines par des coniferes, la survie etait meilleure dans les traitements par monticules et par melange et etait la plus faible dans le traitement de scalpage. Toutes les variables de hauteur avaient tendance a etre superieures dans les traitements de preparation de terrain par melange et par monticules. Finalement, la meilleure estimation de la croissance totale future (regeneration d'epinette et de feuillus combinee) des peuplements domines par des coniferes a ete observee dans la coupe a blanc. En ce qui concerne la croissance de la regeneration d'epinette, la meilleure croissance a ete observee avec 50 % de retention du couvert feuillu et les preparations de terrain par melange du sol et par monticules, oU la croissance projetee de l'epinette etait comparable a celle de peuplements libres de croitre et eduques de la foret boreale de l'Alberta. [Traduit par la Redaction] Mots-cles : peuplement mixte boreal, coupe progressive, preparation de terrain, survie, coupe partielle, plants, retention variable, epinette blanche., Introduction Mixedwood forests of aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench.) Voss) cover extensive areas of the boreal region of Canada, ranging from the Yukon to western [...]

This study presents a model that assesses the potential impact of a new alien insect species, Sirex noctilio Fabricius, on pine timber supply and harvest activities in eastern Canada. We integrate the spread of S. noctilio with a broad-scale growth and harvest allocation model. Projections of pine mortality range between 25 x 106 and 115 x 106 m3 over 20 years depending on S. noctilio spread and impact assumptions. Our model suggests Ontario could experience the highest, most immediate losses (78% of the potential losses across eastern Canada), with Quebec sustaining most of the rest of the losses over the next 20 years. Potential losses of $86 to $254 million per year are simulated after 20 years. The net present value of total harvest losses after 28 years of outbreak ranges between $0.7 to $2.1 billion. Adaptation policies decrease shortterm losses by 46%-55% and delay larger harvest failures by 9-11 years. Without harvest adaptation, failures to maintain annual allowable cut levels may occur once the total area infested exceeds 15 x 106 ha. While better understanding and representing S. noctilio behaviour will involve a significant effort, there is a strong demand by policy makers for this kind of information. Cette etude presente un modele qui evalue l'impact potentiel d'une nouvelle espece d'insecte exotique, Sirex noctilio Fabricius, sur les stocks de bois de pin et les activites de recolte dans l'est du Canada. Les auteurs ont integre la propagation de S. noctilio a un modele de croissance a grande echelle et d'allocation de la recolte. Les projections concernant la mortalite du pin varient de 25 x [10.sup.6] and 115 x [10.sup.6] sur 20 ans selon les hypotheses de propagation et d'impact de S. noctilio. Leur modele indique que l'Ontario pourrait subir les pertes les plus elevees tres tot (78 % des pertes potentielles de tout l'est du Canada) et le Quebec, presque toutes les pertes a venir au cours de la periode s'etendant sur les 20 prochaines annees. Les pertes annuelles pourraient atteindre 86-254 millions $ apres 20 ans. La valeur actualisee nette des pertes totales de recolte apres 28 annees d'epidemie varie de 0,7 a 2,1 milliards $. Des strategies d'adaptation diminueraient les pertes a court terme de 46-55 % et retarderaient les pires recoltes de 9-11 ans. Sans adaptation de la recolte, l'incapacite a maintenir les niveaux de possibilite annuelle de coupe pourrait survenir lorsque la superficie totale infestee depassera 15 x [10.sup.6] ha. Bien que d'importants efforts restent a faire pour mieux comprendre et representer le comportement de S. noctilio, il y a une forte demande de la part des decideurs pour ce type d'informations. [Traduit par la Redaction], Introduction The impact of alien invasive species on timber supply and harvest activities has been identified as one of the most immediate and potentially damaging threats to Canadian forests (Natural [...]

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Copyright of Canadian Journal of Plant Science is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)