Balsam fir trees established from advanced regeneration following a clear-cut in 1970 were pruned in June 1985 to live crown ratios of 0.6, 0.4, and 0.2 compared with control trees, which had live crown ratios of 0.8. After two growing seasons, we investigated the homeostatic adjustment of these trees to the loss of their foliage. The height growth, basal area growth, sapwood cross-sectional area, heartwood area, and sapwood saturated permeability of the trees that were pruned to a 0.6 live crown ratio were not significantly different from those of the controls. On the other hand, height growth increment following pruning was reduced 16.7 cm (23%) and 19.5 cm (27%) for the trees pruned to 0.4 and 0.2 live crown ratios, respectively. Furthermore, basal area growth following pruning was reduced 3.2 cm2 (30%) and 6.5 cm2 (61%), respectively. While trees in both the 0.4 and 0.2 live crown ratio pruning treatments did adjust their breast height sapwood area in response to the removal of foliage, the nature of this adjustment differed between the two treatments. For the trees with the 0.4 live crown ratio, sapwood area was reduced because of a reduction in basal area growth but the area of heartwood remained unchanged. For the trees with the 0.2 live crown ratio, the changes in sapwood area were due both to a reduction in basal area growth and an expansion of the heartwood. The saturated permeability of sapwood was not significantly affected by pruning. The adaptive implications of balsam fir's response to the loss of foliage are discussed in terms of the optimizing the allocation of a limited amount of available carbon.

Effet d'une coupe d'ensemencement et du milieu de germination sur la regeneration des sapinieres boreales riches de seconde venue du Quebec par Patricia Raymond1, Jean-Claude ~u e l l r~ et Marius Pineaul Suite B certaines dCficiences de rCgCn6ration rencontrkes dans les sapinibres borkales riches de seconde venue, une expCrience a Ct C mise en place en 1991 afin de vCrifier les effets du systbme de rCgCn6ration par coupes progressives sur la rCgCnCration du sapin baumier (Abies balsamea (L.) Mill.), de 1'Cpinette blanche (Picea glauca (Moench) Voss) et du bouleau B papier (Betulapapyrifera Marsh). Le plan d'expkrience factoriel en parcelles partagtes comprend la rkduction du couvert forestier (0% et 25% de la surface terribre) en parcelle principale et les milieux de germination (sol minCral, litibre retirke et tkmoin) en sous-parcelle. Les rCsultats de 5 saisons de croissance ont montrC que le milieu de germination Ctait le facteur prCpondCrant B I'installation des recrues, alors que la rkduction du couvert devenait importante au niveau de la survie et de 1'Ctablissement B plus long terme des semis des 3 espbces. La combinaison de la rkduction du couvert de 25 % au traitement du lit de germination minCral a engendrC les meilleures densitCs de rCgCnCration chez les 3 espbces. Les rksultats obtenus jusqu'h maintenant dCmontrent l'importance de combiner la perturbation de l'humus B la coupe d'ensemencement pour atteindre les objectifs de rCgCnCration fix& pour le futur peuplement.Mots-clCs: systbme de rCgCnCration par coupes progressives, sapin baumier, Cpinette blanche, bouleau B papier, rCgCnCration, coupe d'ensemencement, milieu de germination.Stand regeneration failures, sometimes observed in rich second growth balsam fir stands, prompted a study in 1991 to assess the effects of the shelterwood cutting system on regeneration of balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss) and paper birch (Betulapapyrifera Marsh). The factorial experiment design (split-plot) includes forest cover reduction (0 % and 25 % of basal area) in main plots and germination substrate (mineral soil, litter removed and control) in subplots. Results of five growing seasons showed that germination substrate was the main factor determining first-year seedling establishment, and that cover reduction became important for seedling survival and long-term establishment of the three species. A 25 % canopy reduction combined with mineral seedbed treatment resulted in the best regeneration densities of the three species. Thus far, the results demonstrate the importance of combining humus disturbance to seed cutting in order to achieve regeneration goals set for the future stand.Key words: shelterwood cutting system, balsam fir, white spruce, paper birch, regeneration, seed cutting, gemination substrate IntroductionLa facilitt avec laquelle la sapinikre B bouleau blanc vierge se r6gCnbre au Qutbec a ttk affu-mk dans plusieurs ttudes rtalistes dans les anntes 1950 et 1960 dtmontrant l'abondante rtgtnCration prtttab...

White spruce (Picea glauca (Moench.) Voss.) is frequently found in association with balsam fir (Abies balsamea (L.) Mill.) in virgin stands. However, its regeneration is less aggressive than that of balsam fir. The persistance of white spruce in the canopy might be explained by differential mortality and windthrow. Windthrow could play an important role in creating favourable seedbeds and providing increased light. This paper examines the contribution of windthrow for white spruce regeneration in balsam fir-dominated forests. Experimental windthrows were created and regeneration establishment monitored for three seasons. Windthrow greatly modified the availability of seedbeds and enhanced white spruce establishment. Older natural windthrows were sampled to conclude that this effect was still evident more than five years after windthrow occured. We also noticed that white spruce benefited more from the disturbance than did balsam fir. Finally, sampling conducted in mature stands showed that mature white spruce stems were more abundant on the mounds created by old uprootings, indicating that this effect is maintained in the long term. Even though balsam fir also benefited from windthrow, the benefit was proportionally greater for white spruce.Keywords: Picea glauca, Abies balsamea, windthrow, microtopography, regeneration L'épinette blanche (Picea glauca (Moench.) Voss.) est souvent présente comme espèce compagne dans les sapinières vierges. Toutefois, sa régénération est moins agressive que celle du sapin baumier (Abies balsamea (L.) Mill.). La persistance de l'épinette blanche au sein du couvert pourrait s'expliquer par une mortalité différentielle et le chablis. Le chablis pourrait jouer un rôle important en créant des milieux de germination favorables et en augmentant la lumière disponible aux jeunes semis. Cet article aborde la contribution du chablis à la régénération de l'épinette blanche dans des peuplements dominés par le sapin. Des chablis simulés ont été créés et l'installation de la régénération a été suivie sur trois ans. Le chablis a fortement modifié la disponibilité des milieux de germination et a favorisé l'établissement de l'épinette blanche. Des chablis naturels plus anciens ont été échantillonnés, ce qui nous a permis de constater que cet effet était toujours évident, cinq ans ou plus après le renversement des arbres. L'épinette a davantage profité de la perturbation que le sapin. Finalement, un échantillonnage de peuplements matures a permis de constater que les tiges matures d'épinette se retrouvaient davantage sur les monticules formés par le chablis, indiquant que les bénéfices constatés lors de l'installation de la régénération peuvent se prolonger à plus long terme. Même si la régénération du sapin a aussi profité du chablis, le bénéfice était proportionnellement supérieur pour l'épinette blanche.

The use of partial cutting in balsam fir stands has been greatly restricted by the fear of windthrow. This applies to shelterwood cutting, for which very little quantitative information on windthrow is available. This study was conducted in 50-yr-old balsam fir stands. The aim of the study was to quantify windthrow losses associated with three patterns of seed cuts. The study consists of five replicates of four treatments: uncut control, uniform shelterwood, group shelterwood, and strip shelterwood. Complete windthrow monitoring was performed at 2, 4, and 6 yr after cutting. The effect of treatment, wind exposure, and stand characteristics was assessed after 6 yr. A simulation with the ForestGales model was conducted to better understand the seed cut pattern effect in identical stands. Results showed that a shelterwood method involving a low intensity seed cut can be applied in relatively sheltered balsam fir stands. Topographic exposure and stand characteristics did not contribute to the amount of windthrow observed. The major factor explaining the amount of windthrow seems to be the presence of adjacent cuts that funneled wind into the plots. North J. Appl For.20(1):5–13.

partir de placettes permanentes ayant des densit& comparables, dCmontre un ordre relatif de la productivit6 des types kologiques tout B fait semblable B l'ordre relatif de lew indice de qualit6 de station. Ces groupes de placettes, qui Ctaient sous-stockkes, prksentaient des accroissements annuels moyens de 2,9,2,0 et 1,5 m3/ha/an pour des stations de classes I+, I-et 11. Les principaux factem hlogiques qui influencent la f d t 6 de ces stations bodales sont la classe de drainage et la presence de drainage oblique. Par contre, 1'Cpassew du dCpSt et, dans une moindre mesure la textwe, semblent Stre des facteurs moins determinants dans cette zone climatique humide. I1 faut enfin noter que les coefficients de variation des indices de qualit6 de station sont importants B l'intkriew d'un m8me type Ccologique.Balsam fir (Abies balsamea (L) Mill.) site indices (height at 50 years at stump height) were estimated for the principal ecological types of the boreal and humid balsam fir-white birch climatic subdomain in central QuCbec. Ecological types consisted of units homogeneous as to their geomorphological deposit, their drainage class and vegetation dynamic. Mean site index varied from 15.9 m for rich mesic seepage sites to 9.4 m for very thin and poorly drained sites. To the three productivity classes generally used for boreal balsam fir stands in Quebec (Linteau 1955), ow results demonstrated the need to recognize a fourth class to distinguish operational groups. Rich mesic seepage sites are clearly more productive than other mesic sites with which they were grouped in the past. The proposed classes are: 1) I+ (SI > 15 m) comprising rich seepage sites; 2) class I-, comprising mesic sites (SI from 13.5 to 15 m); 3) class II (SI from 10.5 to 13.4 m) which comprises sites that possess moderate growth h itations including imperfectly drained sites, thin (< 50 cm) mesic sites and coarse textured dry sites; 4) and class III (SI c 10.5 m) comprising poorly drained sites. Growth studies of fow ecological types based on permanent plots of similar densities, show the same relative order in productivity as the one established with their site indices. Mean annual growth of these somewhat understocked plots were 2.9,2.0 and 1.5 m3/ha/year for classes I+, Iand I1 respectively. The principal ecological variables that influenced fertility of these boreal sites were drainage class and the presence of seepage. Soil depth and, to a point, soil textwe were not very significative variables in this humid climatic zone. It must also be emphasized that all site indices of ecological types showed high variability.