Acceptabilité visuelle de coupes forestières pour la pessière noire : comparaison de la coupe à blanc traditionnelle et de différents types de rétention végétale chez divers groupes d’intérêt issus d’une région ressource forestière

En pessière noire, le procédé de récolte habituel est celui de la coupe avec protection de la régénération et des sols (CPRS), un procédé de coupe totale. Socialement, ce type de pratique est mal perçu principalement pour ses impacts visuels. Toutefois, il existe pour les écosystèmes boréaux, d’autres procédés de récolte adaptés, issus de l’aménagement écosystémique. Cette étude présente une comparaison de l’acceptabilité visuelle des traitements sylvicoles permettant une plus grande rétention végétale par rapport à la CPRS (coupe avec protection de la haute régénération (CPHRS), coupe avec protection des petites tiges marchandes (CPPTM) et CPRS avec rétention de bouquets). Elle vérifie aussi si des différences dans les jugements d’acceptabilité existent selon l’appartenance à une région ressource forestière et à certains groupes d’intérêts, tels les environnementalistes, les amateurs de plein-air et d’intérêt général. Il en ressort que la qualité et la quantité de la régénération laissée après coupe influencent le jugement et que les traitements permettant de conserver une structure résiduelle parviennent à mitiger, partiellement, les impacts visuels des méthodes de coupe rase traditionnelles. Finalement, l’appartenance à une région forestière n’influence pas le jugement en ce qui a trait à l’acceptabilité visuelle des coupes. Les différences entre les groupes d’intérêts laissent plutôt croire que ce sont les connaissances reliées au milieu forestier qui influencent le plus le jugement.

Impact à court terme de l'exploitation forestière sur le tétras du Canada (Falcipennis canadensis)

Le suivi télémétrique de 35 tétras du Canada (Falcipennis canadensis) 1 an avant coupe forestière et de 22 autres l'année de la coupe montrent que cette espèce est négativement affectée par la coupe à blanc. Après coupe, les tétras se sont réfugiés dans les habitats résiduels, à proximité du domaine vital printanier. Ils furent rencontrés plus souvent dans des peuplements en régénération, à densité arbustive élevée, et dans des milieux improductifs, sélectionnant parmi les habitats disponibles ceux ayant les plus grandes densités arborescentes et les plus faibles densités arbustives. Les déplacements totaux des tétras ont augmenté pendant et après coupe. Les domaines vitaux d'été étaient de 23-41 ha l'année de la coupe contre 13-33 ha l'année précédente (p = 0,07). La superficie des domaines vitaux ne différait pas statistiquement avant (4-21 ha) et après coupe (19-23 ha). La proportion d'individus au repos a diminué après coupe et les comportements d'alerte ont augmenté (p > 0,01). Le taux de survie des tétras a été plus faible l'année de la coupe (S = 0,44 ± 0,02) que l'année précédente (S = 0,75 ± 0,01). Il fut également plus faible après coupe (S = 0,50 ± 0,02) qu'avant les opérations forestières (S = 0,89 ± 0,09), la prédation étant la principale cause de mortalité. La densité des tétras a diminué de 60% après la coupe.

Évolution de la régénération de peuplements résineux et mélangés au cours des 30 années après coupe à blanc mécanisée

This paper presents results from a 30 year monitoring of 15 clearcut areas. Study areas were located before cutting in stands having an abundant advance regeneration. Four study areas were initially dominated by black spruce, four by balsam fir, three by jack pine and the last four comprised a mix of species. Stand inventories and regeneration surveys were conducted before harvesting. Harvesting was done in regular logging operations, without any special care to protect the advance growth. Regeneration surveys were taken again after harvesting, 5 years, 10 years, 20 years and 30 years after harvesting. Black spruce stands regenerated to black spruce dominated stands. Balsam fir, which was sometimes abundant in the advance regeneration, did not invade the stands and the abundance of hardwoods was temporary. In some cases a reduction in yield is to be expected. In balsam fir stands, harwoods were more aggressive. A reduction in softwood yield is predicted for three of the four cutovers. The presence of a tall regeneration seems to lead to higher yields in black spruce and balsam fir stands. The evolution of jack pine and mixed stands is quite variable. In some jack pine stands, hardwoods will constitute a significant component of the new stand. In some mixed stands, softwoods are not very abundant whereas in others they form an important part of the stand at 30 years. This study has shown an urgent need for a better understanding of stand dynamics in young stands. Such an understanding is necessary for an adequate forecast of the yield of second growth stands.

Effets de la coupe à blanc et de la coupe par bandes sur la régénération obtenue après 5 ans dans des pessières noires du Québec

An experiment was conducted to compare the effects of traditional clear-cutting with those of strip cutting on regeneration of black spruce, Piceamariana (Mill.) B.S.P., stands on scarified and unscarified uplands and on lowlands. To that effect, regeneration surveys were done before cutting, in the following year, and 3 and 5 years after cutting. Five years after harvesting, strip cutting led to higher coniferous stocking than clear-cutting on scarified uplands and on lowlands. On unscarified uplands, the gain attributable to strip cutting was not significant. The coniferous stocking of strip cuts on scarified uplands was not greater than on unscarified uplands. So the efficiency of scarification could not be proved in that study. Stocking obtained after 5 years remained closely related to the one observed immediately after harvesting in the strip cufs as in the clear-cuttings. This is particularly true for balsam fir, Abiesbalsamea (L.) Mill. In the strip cuts, the balsam fir stocking was constant while the one of black spruce increased. This could have an impact on the evolution of the composition of the new stands and, consequently, on their vulnerability to spruce budworm, Choristoneurafumiferana (Clem.). The majority of the clear-cuttings were well regenerated 5 years after harvesting. Their average coniferous stocking was slightly above 60%. However, 48% of the clear-cuttings did not reach this level when only unscarified plots on uplands were considered. Advance growth was abundant in those plots but suffered high losses during harvesting. Consequently, reducing the losses during harvesting would result in a lower proportion of clear-cuttings with insufficient coniferous stocking 5 years after cutting. On the other hand, almost all the strip cuts with insufficient regeneration after harvesting were well regenerated 5 years later. Thus, strip cutting could be an interesting option on sites with insufficient advance growth and on sites well regenerated before cutting but where important losses during harvesting are anticipated.

Impact de la tordeuse des bourgeons de l'épinette [Choristoneura fumiferana (Clem.)] sur la régénération des sapinières après la coupe à blanc

An analysis of over 100 balsam fir [Abies balsamea (L.) Mill.] stands has shown some effects of spruce budworm defoliation on regeneration after clearcutting. Even though softwood stocking was consistently high prior to harvesting operations, longer infestation periods or more severe defoliation levels led to a decrease in the stocking of softwood stems above 50 cm height and to the establishment and development of hardwood advance growth. Hardwoods were more often in a dominant position in the most severely damaged stands and the budworm effect was still persistent on the regeneration structure even 5 years after logging. Cutovers with less than 60% stocking were also more frequent in the most severely devastated fir stands. This situation seemed directly related to the impact of the spruce budworm on balsam fir advance growth. Key words: balsam fir, Choristoneura fumiferana, advance growth, clearcutting

Abondance de la régénération 5 ans après la coupe à blanc mécanisée de peuplements d'épinette noire (Piceamariana)

Regeneration was studied 5 years after harvesting on 128 permanent blocks located before logging in black spruce (Piceamariana (Mill.) BSP) stands. Regeneration after 5 years was related to the abundance of advance growth, mainly black spruce layers. Regeneration also differed with the harvesting system used. Best results were obtained with the use of feller-forwarders while tree-length harversting gave the lowest softwood stockings. Regional climax and soil texture also had an effect, mostly by modifying the advance growth abundance. The better softwood stocking observed on thick humus and in the black spruce -moss climax zone was related to higher precutting regeneration levels. The regeneration problems observed on coarse textured soils were also associated with initial differences in the amount of advance growth. The duration of spruce budworm (Choristoneurafumiferana (Clem.)) infestations seemed to have an impact on the regeneration of the stands studied. Hardwoods regeneration, mostly white birch (Betulapapyrifera (Marsh.)), became established after logging or after defoliation by the spruce budworm. Their abundance was also dependent on regional climax and soil texture.

Reproduction de l'épinette noire (Piceamariana) après coupe à blanc de superficie réduite

Small clear-cuttings (elliptical, circular, and strip) were made in the commercial boreal forest in Quebec to improve black spruce (Piceamariana (Mill.) B.S.P.) reproduction.Five years after cutting, black spruce layers were as numerous as black spruce seedlings and total softwood reproduction averaged 26 710 stems per hectare (10 810 stems per acre) with 90% stocking. In some cases, white birch stems tripled between the 1st and 5th year after cutting, which may have an important effect on stand composition.Strip cuts gave more stems per hectare than circular or elliptical cuts but stocking was lower. Strips 40 m wide (130 ft) gave better results than those 80 m wide (260 ft).Stocking, although adequate in all these small clear-cuttings, appears to be a more critical factor in the success of softwood reproduction than is density.