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We modelled the potential impact of intensification of plantation management and thinning, on timber supply of an ~500 000 ha forest in Alberta, Canada over a 200-year planning horizon. Pre-commercial and commercial thinning were applied to a portion of the better sites, which allowed shortening of the time to merchantability and earlier harvest than unthinned stands; less than 25% of the forest was thinned over the course of the plan. The sustainable harvest rate, represented here as the annual allowable cut (AAC), increased by ~14% above baseline, when thinning was applied. Similarly, there was a 20.7% increase in AAC projected with the relaxation of even flow rules if thinning was also applied. Finally, thinning offset the expected decline in AAC after a 20-year surge in cutting of mature pine, designed to slow an epidemic of mountain pine beetle. In terms of wood supply, the volume extracted at thinning was Key words: forest management, intensive, timber, thinning, triad, Introduction Intensive management systems, i.e., including planting to achieve full site occupancy, vegetation management, and pre-commercial and commercial thinning, have been slow to be adopted at a forest level, on [...]

We modelled how pre-commercial and commercial thinning affects development of merchantable timber, specifically large sawlogs (>20 cm diameter), on various site qualities and at different harvest ages. Data from juvenile permanent sample plots from post-harvest regenerated lodgepole pine stands in Alberta were projected using the Mixedwood Growth Model (MGM 21). Pre-commercial thinning (PCT) and different levels of commercial thinning (CT) with PCT were assessed on stands of good, medium, and fair site quality. Results show site quality alone had the greatest impact on merchantable yields with good sites producing ~1.5 times the yield of medium and ~4.3 times that of the fair sites. Moderate thinning on good sites produced a greater quantity of large sawlogs (>20 cm diameter) and their associated volume over unthinned stands than that on medium or fair sites, though thinning positively influenced total yield on these sites as well. On good sites, at age 50, CT treatments produced about ~50 [m.sup.3]/ha more volume of large sawlogs (>20 cm) than the control; such gain drops to 18 [m.sup.3]/ha on medium sites. In addition, the mean annual increment culminated earlier on good sites, also enabling earlier harvest. Key words: commercial and pre-commercial thinning, lodgepole pine plantations, intensive management, thinning from below, shorter rotation Nous avons modelise la facon dont les eclaircies precommerciales et commerciales affectent le developpement du bois marchand, en particulier les grosses billes de sciage (> 20 cm de diametre), sur diverses qualites de site et a differents ages de recolte. Nous avons projete les donnees provenant de placettes-echantillons permanentes juveniles de peuplements de pin tordu latifolie regeneres apres recolte en Alberta a l'aide de la modelisation de la croissance du bois mixte (MGM 21). Nous avons evalue l'eclaircie precommerciale (EPC) et differents niveaux d'eclaircie commerciale (EC) avec l'EPC dans des peuplements de bonne qualite, de qualite moyenne et de qualite passable. Les resultats montrent que la qualite du site a elle seule a eu le plus grand impact sur les rendements marchands, les bons sites produisant ~1,5 fois le rendement des sites moyens et ~4,3 fois celui des sites passables. Une eclaircie moderee sur les bons sites a produit une plus grande quantite de grosses billes de sciage (> 20 cm de diametre) et leur volume associe par rapport aux peuplements non eclaircis que sur les sites moyens ou passables, bien que l'eclaircie ait egalement influence positivement le rendement total sur ces sites. Sur les bons sites, a l'age de 50 ans, les traitements d'eclaircies commerciales ont produit environ ~50 [m.sup.3]/ha de plus de volume de grosses billes de sciage (> 20 cm) que le temoin; ce gain tombe a 18 [m.sup.3]/ha sur les sites moyens. En outre, l'accroissement annuel moyen a culmine plus tot sur les bons sites, ce qui permet egalement une recolte plus precoce. [Traduit par la Redaction] Mots-cles : eclaircie commerciale et precommerciale, peuplements de pin tordu latifolie, gestion intensive, eclaircie par le bas, rotation plus courte, 1. Introduction Thinning and density control of forests has been used in many parts of the world to increase the flow of valuable forest products (e.g., Bergh et al. 2005; [...]

Peatlands with ground surfaces near the water table may be sensitive to disturbances that reduce this distance to water. Shrubby rich fens (SRF) in northern Alberta, Canada, are restricted to the wettest landscape positions and are characterized by brown mosses and stunted trees on weakly consolidated and saturated substrates. In situ oil sands exploration (OSE) practices have established thousands of drilling pads to explore for deeply buried bitumen deposits, with many located on peatlands. In the development of OSE pads on peatlands, the vegetation layer is removed, eliminating the functionally important hummock‐hollow surface topography. We examined the spontaneous regeneration of bryophytes and vascular plants and surface microtopography on SRF, 7 and again 14 years after pad abandonment. In both sampling years, drilling pad surfaces were closer to the water table (mean pad elevation 2012 = 3.3 cm, 2019 = 5.6 cm) and had minor topography compared to adjacent reference habitat. We found, however, over the 7 years, that for both drilling pads and reference habitat, bryophyte and vascular plant richness decreased, and most species declined in frequency. Furthermore, for pads and reference habitat, density of tree seedlings decreased, and expansion of hummock‐forming mosses was limited. Findings suggest that drilling pads and their natural counterparts on SRF may be prone to episodic reductions in plant diversity and ecosystem retrogression, likely resulting from prolonged surface saturation during summers with high rainfall. Because of their wet landscape positions and environmental vulnerability, SRF are likely the peatland habitats slowest to recover following OSE pad construction. [ABSTRACT FROM AUTHOR]

Strict forest renewal policies in western Canada focus on replicating the stand type that was cut and projecting the growth of young stands forward using simple models based upon past growing conditions. These policies arose from European principles of sustained yield and now limit options for adaptive management at the time of investment in forest renewal of public lands. We assert that such simple and restrictive policies, combined with long-term yield predictions, give a false sense of sustainability in times of increased drought, fires, and insect and disease attacks that accompany climate change. We must undertake comprehensive changes in forest policy that incorporate disturbance in our forest management planning. This is a large task! Options include (i) zoning public forests to vary intensities of management and minimize risk; (ii) changing stand- and forest-level models to increase the diversity of forests regenerated; (iii) widening the sphere of scientific experts that can influence forest policy and risk management; and (iv) reallocating expenditures on forest renewal, protection, and management to minimize negative impacts of disturbance. Such a comprehensive overhaul of forest management will be necessary as the current assumptions of forest sustainability come under further scrutiny by the public and investors. Key words: forest management, regeneration policy, risk of disturbance, sustained yield, fire. Resume : Des politiques strictes de renouvellement des forets dans l'ouest du Canada mettent l'accent sur le retour du type de peuplement qui a ete coupe et la projection de la croissance des jeunes peuplements a l'aide de modeles simples fondes sur des conditions de croissance passees. Ces politiques sont issues des principes europeens de rendement soutenu et limitent a present les options de gestion adaptative au moment d'investir dans le renouvellement des forets sur les terres publiques. Nous maintenons que ces politiques simplistes et restrictives, combinees aux predictions de rendement a long terme, donnent un faux sentiment de durabilite alors qu'augmentent les secheresses, les feux et les invasions d'insectes et de maladies qui accompagnent les changements climatiques. Nous devons proceder a des changements importants des politiques forestieres qui incorporent les perturbations dans notre planification de l'amenagement forestier. Il s'agit d'une tache enorme! Les options incluent (i) zoner les forets publiques pour varier l'intensite de l'amenagement et minimiser les risques; (ii) changer nos modeles a l'echelle du peuplement et de la foret pour augmenter la diversite des forets qui sont regenerees; (iii) elargir la sphere des experts scientifiques pouvant influencer les politiques forestieres et la gestion du risque; et (iv) reallouer les depenses reliees au renouvellement de la foret, a la protection et a l'amenagement pour minimiser les impacts negatifs des perturbations. Un remaniement de cette ampleur de l'amenagement forestier sera necessaire a mesure que les hypotheses courantes de durabilite de la foret seront davantage soumises a un examen rigoureux du public et des investisseurs. [Traduit par la Redaction] Mots-cles: amenagement forestier, politique de regeneration, risque de perturbation, rendement soutenu, feu., Introduction Disturbance has played a large role in the boreal forests of western Canada, especially in the last two decades. Infestations of mountain pine beetle (Dendroctonus ponderosae Hopkins, 1902) (Bentz [...]

The recent expansion of mountain pine beetle (MPB, Dendroctonus ponderosae) from its native range in western North America into northern boreal pine forests in Alberta, Canada has resulted in conditions for tree regeneration that are dramatically different from those after wildfire, the predominant natural disturbance in these forests. We assessed natural regeneration post-MPB for northern boreal lodgepole pine sites in Alberta, Canada via intensive surveys of small plots at 33 severely attacked pine stands and using data from 205 permanent sample plots representing various site types and levels of MPB mortality. We used model selection to identify factors explaining regeneration. Overall, pine regeneration was very poor 6–9 years post-MPB; only 42% of the 33 intensively surveyed plots and only 9% of the 205 permanent plots had pine seedlings. This poor regeneration is attributed to high levels of cone serotiny in these populations, unsuitable regeneration microsites due to undisturbed litter or feathermoss layers, and competition from the residual canopy and understory vegetation. Other species (aspen, birch, poplar, and black and white spruce) were found on most sites, either as post-attack regeneration or regeneration established in advance. Without intervention, many of these stands will likely transition away from pine, to broadleaf and other conifer species. [ABSTRACT FROM AUTHOR]

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 [...]

Wooded rich fens (WRF), characterized by high variation in surface topography and numerous plant species organized along microtopographic gradients, are abundant in continental western Canada. In regions where in situ oil sands exploration (OSE) prevails, however, winter operations eliminate the surface vegetation and mechanically flatten the exposed peat. This results in saturated or flooded soils during the growing season and eliminates plant species dependent on naturally elevated microhabitats, with implications for peatland recovery. In northeastern Alberta, we redeveloped hummock topography on replicate WRF after OSE by extracting blocks of frozen peat from peatland surfaces in the winter. Peat mounds and adjacent unmounded flattened areas were left to regenerate naturally and were sampled four to five summers later. Mounds facilitated the colonization of many peatland plants not adapted to waterlogged soils. For bryophytes, mean richness and diversity of liverworts, Sphagnum, and true mosses were higher in mounded plots than in unmounded plots. For vascular plants, woody plants (trees and shrubs) had higher richness, cover, and diversity (trees only) in mounded plots. Peat mounding may be effective for stimulating vegetation development on OSE-degraded WRF. All mounds, however, will require lateral expansion by hummock-forming mosses to provide the habitat volume required for development of large woody plants. Key words: microtopography, oil sands exploration, peatland restoration, Sphagnum, wooded rich fen. Les tourbieres boisees minerotrophes (TBM) sont abondantes dans la region continentale de l'ouest du Canada. Elles sont caracterisees par une grande variation topographique de surface et la presence de nombreuses especes vegetales distribuees le long de gradients microtopographiques. Cependant, dans les regions oU l'exploration des sables bitumineux (ESB) domine, les operations hivernales eliminent la vegetation de surface et aplanissent mecaniquement la tourbe qui est exposee. Cela entrarne la saturation ou l'engorgement des sols durant la saison de croissance et elimine les especes vegetales qui dependent de microhabitats naturellement sureleves, ce qui a des repercussions sur la recuperation des tourbieres. Dans le nord-est de l'Alberta, nous avons recree la topographie de hummocks dans plusieurs TBM apres l'ESB en extrayant des blocs de tourbe gelee a la surface de tourbieres en hiver. On a laisse les monticules de tourbe et les zones aplanies adjacentes sans monticules se regenerer naturellement et un echantillonnage a ete realise quatre a cinq etes plus tard. Les monticules ont facilite la colonisation de plusieurs plantes des tourbieres qui ne sont pas adaptees aux sols gorges d'eau. Dans le cas des bryophytes, la diversite et la richesse des hepatiques, des sphaignes et des vraies mousses etaient en moyenne plus grandes dans les places echantillons avec des monticules que sans monticules. Dans le cas des plantes vasculaires, la richesse, le recouvrement et la diversite (arbres seulement) des plantes ligneuses (arbres et arbustes) etaient plus eleves dans les places echantillons avec des monticules. La creation de monticules de mousses peut etre efficace pour promouvoir le developpement de la vegetation dans les TBM degradees a la suite de l'ESB. Cependant, une expansion laterale des monticules par les mousses qui forment les hummocks sera necessaire pour fournir le volume d'habitat requis pour le developpement de grosses plantes ligneuses. [Traduit par la Redaction] Mots-cles : microtopographie, exploration des sables bitumineux, sphaignes, restauration des tourbieres, tourbiere boisee minerotrophe., Introduction Peatlands are critically important wetland ecosystems because of the numerous functional and biological roles that they have on landscapes (Vitt 2006; Minayeva et al. 2017). Peatlands account for approximately [...]

Given a seed source, the quality of available substrates is a key factor in determining the success of white spruce (Picea glauca (Moench) Voss) natural regeneration. We examined the influence of substrate and competing vegetation on survival and growth of natural regeneration of white spruce up to 4 years following harvesting in deciduous-dominated upland boreal mixedwood sites. Feather moss, thick soil surface organic layers, litter, and solid wood were poor substrates for establishment. Early successional mosses establishing on mineral soil, thin organics, and rotten wood were generally favourable microsites but were not highly available on postharvest sites. Mineral soil substrates were not as suitable as expected, likely because on a postlogged site, they are associated with unfavourable environmental characteristics (e.g., low nutrient availability, exposure). There was some evidence that survival and growth of seedlings were improved by surrounding vegetation in the first years, but heavy competing vegetation had a negative impact on older seedlings. Burial by aspen litter greatly increased seedling mortality, especially when combined with a brief period of submergence due to heavy spring snowmelt. The results provide insight into conditions under which natural regeneration could be an option for establishing white spruce following harvesting of deciduous-dominated boreal mixedwood forests. Key words: natural regeneration, white spruce, substrate, seedling survival, competing vegetation, forest management. Pour une source de graines donnee, la qualite des substrats disponibles est un facteur cle pour le succes de la regeneration naturelle d'epinette blanche (Picea glauca (Moench) Voss). Nous avons etudie l'influence du substrat et de la vegetation concurrente sur la survie et la croissance de la regeneration naturelle d'epinette blanche jusqu'a 4 ans apres la coupe de peuplements mixtes boreaux domines par des especes decidues et etablis sur des stations bien drainees. Les mousses hypnacees, les couches epaisses de matiere organique sur le sol, la litiere et le bois massif constituaient de mauvais substrats pour l'etablissement des semis. Les mousses de debut de succession etablies sur le sol mineral, les couches minces de matiere organique sur le sol et le bois decompose constituaient generalement des microsites favorables, mais etaient peu disponibles sur les stations recoltees. Les substrats formes de sol mineral n'etaient pas aussi appropries que prevu, probablement parce que sur une station qui a ete recoltee, ils sont associes a des caracteristiques environnementales defavorables (p. ex.: faible disponibilite des nutriments, exposition). La survie et la croissance des semis ont montre des signes d'amelioration lies a la presence de vegetation environnante au cours des premieres annees, mais une forte competition exercee par cette vegetation a eu un impact negatif sur les plus vieux semis. L'ensevelissement des semis par la litiere de peuplier a considerablement augmente leur mortalite, particulierement lorsqu'il etait jumele a une breve periode d'immersion causee par une importante fonte des neiges au printemps. Les resultats donnent un apercu des conditions dans lesquelles la regeneration naturelle pourrait constituer une option pour l'etablissement de l'epinette blanche apres la recolte des forets mixtes boreales dominees par des especes decidues. [Traduit par la Redaction] Mots-cles: regeneration naturelle, epinette blanche, substrat, survie des semis, vegetation concurrente, amenagement forestier., Introduction White spruce (Picea glauca (Moench) Voss) is an economically and ecologically important conifer that is widely distributed across the boreal forests of North America. On upland mixedwood sites that [...]

In this study, we tested the efficacy of establishing lodgepole pine (Pinus contorta Dougl.) from seed using woody mulch produced from slashed tree tops from a pine harvesting site; this mulch contained the closed serotinous cones of the lodgepole pine. Mulch was spread on prepared reclamation sites at depths of 0,1, 3, and 5 cm. Broadcast seeding of pine was also done at mulch depths of 0 and 1 cm. Mulch cover that was 1 cm thick was the preferred treatment, as it produced 17 000 seedlings x [ha.sup.-1] by the third year after treatment while being similar in seedling density to the 3 and 5 cm treatments. When 50 000 seeds x [ha.sup.-1] were added, seedling density went up more on the sites with 1 cm of mulch than the sites with no mulch. Soil temperature was lower and temperature extremes were reduced under the mulch layer compared with the control plot. The plots with 1 cm of mulch also had higher soil moisture in the mineral layer than the plots with 0 cm of mulch. A thin layer of woody mulch, therefore, provided a source of pine seed and the covering of the ground provided a more benign environment for the establishment of pine germinants. Key words: lodgepole pine, mulch, reclamation, regeneration, recruitment. Dans cette etude, nous avons teste l'efficacite d'etablissement du pin tordu (Pinus contorta Dougl.) a partir de graines en utilisant un paillis ligneux provenant des houppiers de pins abattus dans une aire de coupe; ce paillis contenait des cones serotineux fermes de pin tordu. Le paillis a ete etendu selon des epaisseurs de 0,1, 3 et 5 cm sur des stations preparees pour leur mise en valeur. L'ensemencement a la volee du pin a egalement ete effectue avec les paillis d'une epaisseur de 0 et 1 cm. Le paillis d'une epaisseur de 1 cm etait le meilleur traitement puisqu'il a produit 17 000 semis x [ha.sup.-1] trois ans apres le traitement, ce qui etait semblable a la densite de semis des traitements de 3 et 5 cm d'epaisseur. Lorsque 50 000 graines x [ha.sup.-1] avaient ete ajoutees au paillis, la densite des semis etait plus elevee sur les stations couvertes par un paillis de 1 cm d'epaisseur que sur les stations sans paillis. Comparativement au temoin sans paillis, la presence d'un paillis a provoque une diminution de la temperature du sol et des extremes de temperature. Les placettes couvertes par un paillis de 1 cm d'epaisseur avaient aussi un sol mineral plus humide que les placettes sans paillis. Une mince couche de paillis ligneux constitue donc une source de graines de pin et un couvert protecteur du sol produisant un environnement plus clement pour l'etablissement des plantules de pin. [Traduit par la Redaction] Mots-cles : pin tordu, paillis, mise en valeur, regeneration, recrutement., Introduction Lodgepole pine (Pinus contorta Dougl.) populations dominate much of the landscape in the lower foothills ecoregion of Alberta (Ecological Stratification Working Group 1996), where they are subjected to multiple [...]

An operational-scale transfer of salvaged forest floor material (FFM) containing trembling aspen (Populus tremuloides Michx.) roots was done to explore its feasibility for aspen forest restoration on heavily disturbed lands. This technique takes advantage of aspen's ability of regenerate vegetatively from root fragments. Surface soils from an intact 4 ha aspen forest were salvaged at two depths (15 cm and 40 cm) and immediately placed onto a reclamation site of the same size and at the same two depths. Over the next two growing seasons, aspen sucker density, mortality, and height growth were assessed in relation to root fragment density, burial depth, and root fragment size. Sucker density, height growth, and survival increased with salvage and placement depth, likely related to the fact that deeper salvage depths allowed for more roots to be in good mineral soil contact and proportionately fewer roots to be placed close to the surface (0-5 cm), decreasing their risk of exposure. Large- diameter root fragments buried deeper than 20 cm did not produce viable suckers, so placement of FFM thicker than 20 cm cannot be recommended for the vegetative regeneration of aspen. However, if possible, a deeper salvage of the FFM that contains the aspen root system could allow the material containing the roots to be spread over a larger area and still achieve vegetative regeneration of aspen from suckering, although the overall root propagule density is lower. Key words: forest floor salvage, forest restoration, Populus tremuloides, vegetative regeneration and growth, application depth. Un transfert a l'echelle operationnelle de materiel recupere de la couverture morte (MRCM) contenant des racines de peuplier faux-tremble (Populus tremuloides Michx.) a ete realise pour explorer sa faisabilite dans le cadre de la restauration des peupleraies sur des terrains fortement perturbes. Cette technique tire profit de la capacite du peuplier a se regenerer vegetativement a partir de fragments de racine. La surface du sol d'une peupleraie intacte de 4 ha a ete recuperee selon deux profondeurs (15 cm et 40 cm) et a ete immediatement placee sur une station a valoriser de la meme taille en conservant les deux memes profondeurs. Au cours des deux saisons de croissance suivantes, la densite, la mortalite et la croissance en hauteur des drageons de peuplier ont ete evaluees en fonction de la densite des fragments de racine, de la profondeur d'enfouissement et de la taille des fragments de racine. La densite, la croissance en hauteur et la survie des drageons ont augmente avec l'epaisseur du materiel recupere et mis en place. Ce resultat est probablement relie au fait qu'une recuperation plus profonde permet a un plus grand nombre de racines d'etre en contact etroit avec le sol mineral et a proportionnellement moins de racines de se retrouver pres de la surface du sol (de 0 cm a 5 cm), ce qui diminue leur risque d'exposition. Les fragments de racine de gros diametre enfouis a une profondeur inferieure a 20 cm n'ont pas produit de drageons viables, de telle sorte que la mise en place de MRCM plus epais que 20 cm ne peut etre recommandee pour la regeneration vegetative du peuplier. Toutefois, si possible, une recuperation plus profonde de MRCM contenant le systeme racinaire de peupliers pourrait permettre au materiel contenant les racines d'etre etendu sur une plus grande surface tout en obtenant une regeneration vegetative de peuplier par drageonnage, bien que la densite totale de propagules de racine soit plus faible. [Traduit par la Redaction] Mots-cles : recuperation de la couverture morte, restauration forestiere, Populus tremuloides, regeneration et croissance vegetative, profondeur d'application., Introduction Mineral and energy resources are often found in forested regions, which are consequently subjected to severe disturbances and in need of large-scale forest reclamation and restoration (World Resources Institute [...]

Most forest managers view natural regeneration of Picea glauca (white spruce) after forest harvesting to be unreliable; in this paper the Authors dispute this idea by describing the factors influencing natural regeneration of spruce, i.e., seed production, dispersal, germination and seedling establishment and discussing the opportunities for encouragement of natural regeneration after logging. Seed supply is greatest from trees with large crowns, that are positioned in the upper canopy and seeding is greatest in mast years. Maintaining at least five mature white spruce trees per hectare within cut areas or dense stands of spruce on edges of cutovers ensures pollination success as well as even seed distribution. The most suitable seedbeds for white spruce germination are mineral soil, mineral soil with a thin organic layer, or large downed rotten logs. Mineral soil seedbeds are available for a short time after fire or other disturbances, while downed wood becomes available over time; this results in recruitment immediately after disturbance or several decades later. To increase the availability of suitable seedbeds the soil can be scarified during or after harvest and nurse logs should be left; on wet sites mounding should be considered. Partial canopy cover can protect seedlings from climate extremes while limiting competing vegetation. Using natural regeneration, a range of stocking outcomes can be expected--from no stocking to overstocking of spruce. Such variation in the amount of spruce versus broadleaf species, however, is consistent with the range of variation in forest composition found naturally in the boreal mixedwood region. Key words: Picea glauca, seed production, seed dispersal, seed germination, establishment, regeneration microsite, forest management. La plupart des amenagistes forestiers considerent la regeneration du Picea glauca (epinette blanche) apres recolte forestiere, comme non fiable; les auteurs remettent en question cette idee en decrivant les facteurs influencant la regeneration de cette epinette, c.-a-d. production des semences, dispersion et germination des graines ainsi que l'etablissement des plantules, puis ils discutent les opportunites d'encourager la regeneration naturelle apres recolte. Les arbres a larges couronnes, situes le plus haut dans la canopee et ou la production est la plus grande les annees de forte production, produisent la majorite des graines. Le maintient d'au mois cinq arbres matures d'epinette blanche par ha sur les sites de recolte, ou encore de denses peuplements d'epinettes au pourtour des surfaces coupees, assurent le succes de la pollinisation ainsi que la distribution de semences. Les lits de germinations les plus propices pour les graines de l'epinette blanche sont les sols mineraux, les sols mineraux avec une mince couche de matiere organique, ou encore les gros troncs pourris au sol. Les lits de germination restent disponibles pendant une courte periode apres le feu, ou autres perturbations, alors que les arbres tombes au sol deviennent disponibles avec le temps; ceci conduit a un recrutement immediat apres la perturbation ou encore des decades plus tard. Pour augmenter la disponibilite des lits de germination propices, on peut scarifier le sol pendant ou apres la recolte et on devrait aussi laisser des billes d'hebergement; on devrait egalement considerer le billonnage sur les sites humides. Une couverture partielle par la canopee peut proteger les plantules contre des conditions climatiques extremes tout en limitant la vegetation competitrice. En utilisant la regeneration naturelle, on peut attendre une gamme de regarnis, allant de l'absence a l'exces de plantules. De telles variations dans la quantite d'epinette versus les especes a larges feuilles, demeurent cependant congrues avec l'ampleur de variation de la composition des forets, rencontree naturellement dans les regions de la foret mixte boreale. Mots-cles: Picea glauca, production de semences, dispersion des graines, dispersion des graines, microsites d'etablissement de la regeneration, amenagement forestier. [Traduit par la Redaction], Introduction Picea glauca (Moench) Voss (white spruce) is a widely distributed tree species of the North American boreal forest that is both economically and ecologically important. It is found across [...]

: In a greenhouse experiment, we tested whether the initiation, density, and growth of trembling aspen (Populus tremuloides Michx.) root suckers are related to postdisturbance soil nutrient availability. After decapitation of functional 2-year-old aspen root systems, nutrient solutions adjusted for various concentrations and forms of mineral N, different concentrations of [Ca.sup.2+], [K.sup.+], or [PO.sub.4.sup.3-], and different pH were applied to the roots and their suckering response was assessed after 35 days. Root systems treated with [NO.sub.3.sup.-] at concentrations of 1.5 and 7.5 mmol/L produced nearly double the sucker density compared with an unfertilized control, while fertilizing with N in the form of [NH.sub.4.sup.+] did not affect sucker numbers, regardless of concentrations. The best growth of suckers was achieved with a mixture of 15 mmol/L [NO.sub.3.sup.-] + [NH.sub.4.sup.+] whereas the lowest growth was observed with 15 mmol/L [NH.sub.4.sup.+]. Neither [Ca.sup.2+], [K.sup.+], and [PO.sub.4.sup.3-] nor the pH tested in this study impacted sucker density or growth. This has implications for understanding the impacts of disturbance on forest succession and the subsequent regeneration of aspen stands. The results suggest that the amount of nitrification, depending on the type and severity of disturbances, will influence the regeneration density of aspen. Resume: Dans une experience en serre, nous avons verifie si l'initiation, la densite et la croissance des drageons racinaires de peuplier faux-tremble (Populus tremuloides Michx.) etaient reliees a la disponibilite des nutriments apres une perturbation. Apres avoir decapite le systeme racinaire fonctionnel de peupliers ages de deux ans, nous avons ajoute des solutions nutritives contenant differentes concentrations et formes de N mineral, differentes concentrations de [Ca.sup.2+], [K.sup.+] ou [PO.sub.4.sup.3-] et ajustees a differents pH. Nous avons evalue le drageonnement apres 35 jours. Les systemes racinaires traites avec [NO.sub.3.sup.-] a des concentrations de 1,5 et 7,5 mmol/L ont produit pres du double de la densite de drageons comparativement au temoin non fertilise alors que la fertilisation avec [NH.sub.4.sup.+] n'a eu aucun effet sur le nombre de drageons peu importe la concentration. La croissance des drageons a ete la plus forte avec 15 mmol/L de [NO.sub.3.sup.-] + [NH.sub.4.sup.+] et la plus faible avec 15 mmol/L de [NH.sub.4.sup.+]. Les [Ca.sup.2+], [K.sup.+] et [PO.sub.4.sup.3-] et les differents pH testes dans cette etude n'ont eu aucun impact sur la densite ou la croissance des drageons. Cela a des consequences sur la comprehension des impacts des perturbations sur la succession forestiere et la regeneration subsequent des peuplements de peuplier. Les resultats indiquent que la quantite de nitrification, dependamment du type et de la severite des perturbations, influencera la densite de la regeneration de peuplier. [Traduit par la Redaction], Introduction Trembling aspen (Populus tremuloides Michx.) is an early successional clonal tree species that re-establishes by root suckering after aboveground disturbances. After the removal or death of the aboveground portion [...]

: In an operational-scale experiment, we examined natural regeneration of white spruce (Picea glauca (Moench) Voss) under various degrees of variable retention harvesting across different overstory canopy compositions. We sampled four types of overstory canopy compositions (ranging from deciduous dominated to conifer dominated) and six rates of retention (2%, 10%, 20%, 50%, 75% and 100%). Spruce seedling densities, maximum height, and stocking rates were assessed in 432 transects and were found to be lowest in the deciduous stands and with 100% canopy retention (control). Regression tree analysis indicated that densities, maximum height, and stocking of spruce seedlings were greatest with higher availability of seed trees (>30*[ha.sup.-1]) and on machine corridors; in these circumstances stocking reached 74%. By contrast, stocking was less than 14% on retention strips with no machine traffic, when seed tree density was less than 11 seed trees*[ha.sup.-1]. However, stocking also declined with higher density of residual trees. Stocking in relation to density of seed trees was highest within clearcuts and lowest within the 75% retention intensity where low light transmission may have limited regeneration success. Passive soil disturbance from skidding appeared to be more important for the establishment of spruce seedlings than was the abundance of competing vegetation. Resume: A l'aide d'une experience a l'echelle operationnelle, nous avons etudie la regeneration naturelle de l'epinette blanche (Picea glauca (Moench) Voss) en fonction de differents degres de coupe a retention variable et de differentes compositions du couvert dominant. Nous avons echantillonne quatre types de composition du couvert dominant (allant d'un couvert domine par des feuillus a un couvert domine par des coniferes) et six taux de retention (2, 10, 20, 50, 75 et 100 %). La densite de semis d'epinette, la hauteur maximale et le coefficient de distribution de la regeneration (CDR) ont ete estimes le long de 432 transects. La densite de semis d'epinette, la hauteur maximale et le CDR avaient les plus basses valeurs dans les peuplements feuillus et dans le traitement a retention de 100 % (temoin). Une analyse par arbre de regression a indique qua la densite, la hauteur maximale et le CDR des semis d'epinette atteignaient les valeurs les plus elevees lorsque la disponibilite des arbres semenciers etait elevee (>30 [ha.sup.-1]) et dans les sentiers de debardage. Dans ces circonstances, le CDR atteignait 74 %. Au contraire, le CDR etait inferieur a 14 % dans les bandes de retention ou la machinerie ne circulait pas lorsque la densite des arbres semenciers etait inferieure a 11 [[ha.sup.-1]. Cependant, le CDR diminuait aussi dans les traitements avec les plus fortes densites d'arbres residuels. En fonction de la densite des arbres semenciers, le CDR etait le plus eleve dans les coupes a blanc et le plus bas dans les coupes a retention de 75 % ou la faible transmission de la lumie re peut avoir limite le succes de la regeneration. Une perturbation passive du sol due au debardage a semble plus importante pour l'etablissement des semis d'epinette que l'abondance de la vegetation concurrente. [Traduit par la Redaction], Introduction Over the last decade, forest managers and silviculturists have increasingly used variable retention harvesting systems as an approach to sustainable forest management that attempts to emulate natural disturbances (Mitchell [...]

Three studies examined the establishment and early growth of trembling aspen (Populus tremuloides Michx.) and balsam poplar (Populus balsamifera L.) from seed. To better understand the differences in initial developmental patterns between both species, we monitored germination and early growth in a washed sand medium with a balanced fertilizer added. Two additional studies used the Ae, Bm, and Bt horizons of a Brunisolic Gray Luvisol soil to test the impact of different soil horizons and conditions (compaction and moisture) on the establishment and early growth of trembling aspen and balsam poplar seedlings. Balsam poplar had faster radicle and leaf area development than trembling aspen and grew similarly in all soil horizons, while trembling aspen only grew well in the Ae horizon, where it outgrew balsam poplar. The superior growth of trembling aspen in the Ae horizon was associated with higher P and organic C relative to the lower horizons. Although germination was lowest on the low-compaction--low-moisture treatment for both species, balsam poplar establishment and early growth were higher than for trembling aspen in all combinations of compaction and moisture. Compared with trembling aspen, the wider establishment niche of balsam poplar is attributed to its faster root development and ability to grow in a range of soil substrates and conditions. Key words: seedling establishment, Populus tremuloides, Populus balsamifera, compaction, moisture, soil horizons, disturbance. Dans trois etudes, les auteurs ont examine l'etablissement et le debut de la croissance du peuplier faux-tremble (Populus tremuloides Michx.) et du peuplier baumier (Populus balsamifera L.) a partir de la graine. Afin de mieux comprendre les differences des patrons du developpement initiaux entre ces deux especes, les auteurs ont suivi la germination et le debut de la croissance sur un substrat de sable lave, en ajoutant un fertilisant soluble balance. Deux etudes supplementaires ont fait appel aux horizons Ae, Bm et Bt d'un luvisol brunisolique gris, destinees a verifier I'impact des differents horizons et de leurs conditions (compaction et humidite) sur l'etablissement et le debut de la croissance des plantules des deux especes de peupliers. Le peuplier baumier developpe ses racines et sa surface foliaire plus rapidement que le peuplier faux-tremble et pousse de la meme facon dans tous les horizons, alors que le peuplier faux-tremble ne pousse bien que dans l'horizon Ae, ou il se developpe plus vite que le peuplier baumier. On associe la croissance superieure du peuplier faux-tremble dans l'horizon Ae avec de plus fortes teneurs en phosphore et en C organique, comparativement aux horizons inferieurs. Bien que la germination soit plus lente avec le traitement faible compaction--faible humidite chez les deux especes. l'etablissement du peuplier baumier et sa croissance initiale sont plus rapides que chez le peuplier faux-tremble, dans toutes les combinaisons de compaction et d'humidite. Comparativement au peuplier faux-tremble, on attribue la plus grande amplitude de la niche d'etablissement du peuplier baumier a son developpement racinairc plus rapide et a sa capacite de se developper dans un ensemble de substrats et de conditions edaphiques. Mots-cles : etablissement des plantules, Populus tremuloides, Populus balsamifera, compaction, humidite, horizons du sol, perturbation. [Traduit par la Redaction], Introduction While trembling aspen (Populus tremuloides Michx.) and balsam poplar (Populus balsamifera L.) reproduce primarily by clonal reproduction (Perala 1990; Zasada and Phipps 1990), there is increasing evidence that reproduction [...]

In some boreal forests sites, there are considerable amounts of natural regeneration of white spruce (Picea glauca (Moench) Voss) after logging, even without silvicultural treatments to encourage establishment. We assessed the factors controlling the amount of this regeneration 8-15 years postharvest on previously aspen-dominated (Populus tremuloides Michx.) boreal mixedwood sites. We surveyed 162 transects across 81 cutovers, exploring the effects of mast years, season of harvest, distribution of seed trees, weather conditions around the time of harvest, and abundance of grass or woody vegetation on white spruce regeneration. Substantial amounts of naturally regenerated white spruce were found; however, sites with no seed trees had virtually no spruce regeneration. Average stocking was 7% (percentage of 9 m2 plots along a transect across a cutover that had at least one seedling), ranging from 0% to 62%. Stocking levels were higher in cutblocks that had been harvested in the summer, prior to seedfall of a mast year, and where there was a seed source within 60 m. Stocking was lower when conditions were cool and wet the year before and 2 years after harvest and when the site contained extensive cover of grass or woody vegetation. Resume: Sur certaines stations forestieres boreales, il y a une quantite considerable de semis naturels d'epinette blanche (Picea glauca (Moench) Voss) a la suite d'une coupe, meme sans traitement sylvicole visant a promouvoir leur etablissement. Nous avons evalue les facteurs qui determinent la quantite de cette regeneration sur des stations coupees il y a 8 a 15 ans et precedemment occupees par des peuplements mixtes boreaux domines par le peuplier faux-tremble (Populus tremuloides Michx.). Nous avons etabli 162 transects repartis dans 81 aires de coupe pour evaluer les effets des annees semencie res, de la saison durant laquelle la coupe a eu lieu, de la distribution des semenciers, des conditions climatiques a l'epoque de la coupe et de l'abondance de la vegetation herbacee et ligneuse sur la regeneration d'epinette blanche. Un nombre substantiel de semis naturels d'epinette blanche a ete inventorie. Cependant, les stations sans semenciers n'avaient pratiquement pas de regeneration d'epinette. Le coefficient de distribution de la regeneration etait en moyenne de 7 % (pourcentage de placettes de 9 [m.sup.2] le long d'un transect etabli dans une coupe ou il y avait au moins un semis) et variait de 0 % a 62 %. Le coefficient de distribution de la regeneration etait plus eleve sur les stations recoltees pendant l'ete, avant la pluie de graines d'une annee semenciere et ou il y avait une source de semences a moins de 60 m. Le coefficient de distribution de la regeneration etait plus faible lorsque les conditions climatiques durant l'annee precedant la coupe et deux ans apres la coupe etaient fraiches et humides et lorsque la station etait abondamment couverte de vegetation herbace e ou ligneuse. [Traduit par la Redaction], Introduction Boreal mixedwood forests composed of trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) are found on mesic and subhygric sites across large portions of North [...]