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In peatlands, microtopography strongly affects understory plant communities. Disturbance can result in a loss of microtopographic variation, primarily through the loss of hummocks. To address this, mounding treatments can be used to restore microtopography. We examined the effects of mounding on the understory vegetation on seismic lines in wooded fens. Seismic lines are deforested linear corridors (~3 to 8 m wide) created for oil and gas exploration. Our objectives were to compare the recovery of understory communities on unmounded and mounded seismic lines and determine how recovery varies with microtopographic position. Recovery was evident in the unmounded seismic lines, with higher shrub and total understory cover at the 'tops' of the small, natural hummocks than at lower microtopographic positions--much like the trends in adjacent treed fens. In contrast, mounding treatments that artificially created hummocks on seismic lines significantly changed understory communities. Mounded seismic lines had higher forb cover, much lower bryophyte cover, less variation along the microtopographic gradient, and community composition less similar to that of the reference sites than unmounded seismic lines due to higher abundance of marsh-associated species. Our results suggest that mounding narrow seismic lines can be detrimental to the recovery of the understory communities in treed peatlands. Key words: moderate-rich fens, linear disturbances, mounding, restoration, understory vegetation. Dans les tourbieres, la microtopographie influence fortement les communautes vegetales de sous-etage. Une perturbation peut entrainer une baisse de variation de la microtopographie, surtout par la perte de monticules. Pour resoudre ce probleme, la creation de monticules peut etre utilisee pour restaurer la microtopographie. Nous avons etudie les effets de la creation de monticules sur la vegetation de sous-etage dans des lignes sismiques traversant des tourbieres boisees. Les lignes sismiques sont des couloirs lineaires deboises (environ 3 a 8 m de large), crees pour l'exploration petroliere et gaziere. Nos objectifs etaient de comparer le retablissement des communautes de sous-etage dans des lignes sismiques avec et sans creation de monticules, et de determiner comment le retablissement varie en fonction de la position microtopographique. Le retablissement etait manifeste dans les lignes sismiques sans creation de monticules, ou le recouvrement d'arbustes et de vegetation totale sur le dessus de petits monticules naturels etait plus grand qu'aux positions microtopographiques inferieures, ce qui tendait aussi a etre le cas dans les tourbieres boisees adjacentes. En revanche, la creation artificielle de monticules dans les lignes sismiques a considerablement change les communautes de plantes de sous-etage. Les lignes sismiques avec des monticules artificiels avaient un recouvrement de plantes herbacees plus eleve, un recouvrement de bryophytes beaucoup plus faible, moins de variation le long du gradient microtopographique, et une composition de la vegetation moins semblable a celle des stations de reference que celle des lignes sismiques non traitees, en raison d'une plus grande abondance d'especes associees aux marais. Nos resultats indiquent que la creation de monticules dans les lignes sismiques etroites peut nuire au retablissement des communautes de plantes de sous-etage dans les tourbieres boisees. [Traduit par la Redaction] Mots-cles: tourbieres moderement riches, perturbations lineaires, creation de monticules, restauration, vegetation de sous-etage., Introduction Forests across the world are experiencing increases in the levels of human disturbance that are influencing their ecological function and biodiversity (Haddad et al. 2015). In regions with oil [...]

Regionally fitted allometric equations for individual trees and root-to-shoot ratio values are normally used to estimate local aboveground and belowground forest biomass, respectively. However, uncertainties arising from such applications are poorly understood. We developed equations for both aboveground and belowground biomass using destructive sampling for three dominant upland boreal tree species in northwestern Alberta, Canada. Compared with our equations, the diameter-based national equations derived for use across Canada underestimated aboveground biomass for Picea glauca (Moench) Voss but gave reasonable estimates for Populus balsamifera L. and Populus tremuloides Michx. The national equations based on both tree diameter and height overestimated aboveground biomass for the Populus species but underestimated it for Picea glauca in our study area. The approach of root-to-shoot ratio proposed by the Intergovernmental Panel on Climate Change (IPCC) overestimated belowground biomass by 16%-41%, depending on forest cover type, in comparison with our values estimated directly on site, with the greatest bias in deciduous-dominated stands. When the general allometric equations for aboveground biomass and the root-toshoot ratio for belowground biomass were combined to estimate stand biomass, overestimation could be as high as 18% in our study area. The results of our study support the development of improved regional allometric equations for more accurate local-scale estimations. Incorporating intraspecific variation of important traits such as tree taper may be especially helpful. Key words: EMEND (Ecosystem Management Emulating Natural Disturbance), intraspecific trait variation, root-to-shoot ratio, tree taper, wood density. On utilise generalement des equations allometriques ajustees a l'echelle regionale pour les arbres individuels et des valeurs du rapport racines-tiges pour estimer respectivement la biomasse forestiere locale, aerienne et souterraine. Cependant, les incertitudes decoulant de telles applications sont mal comprises. Nous avons developpe des equations de biomasse aerienne et souterraine en utilisant un echantillonnage destructif pour trois especes d'arbres boreales dominantes dans les hautes terres du nord-ouest de l'Alberta, au Canada. Comparativement a nos equations, les equations nationales basees sur le diametre developpees pour etre utilisees partout au Canada sous-estimaient la biomasse aerienne de Picea glauca (Moench) Voss, mais donnaient des estimations raisonnables pour Populus balsamifera L. et Populus tremuloides Michx. Les equations nationales basees sur le diametre et la hauteur des arbres surestimaient la biomasse aerienne des especes de Populus L., mais la sous-estimaient pour Picea glauca dans notre zone d'etude. L'approche du rapport racines-tiges, proposee parle Groupe d'experts intergouvernemental sur l'evolution du climat (GIEC), a surestime la biomasse souterraine de 16 a 41% selon le type de couvert forestier par rapport a nos valeurs estimees directement sur le site, le biais le plus important etant observe dans les peuplements domines par les feuillus. En combinant les equations allometriques generales pour la biomasse aerienne et le rapport racines-tiges pour la biomasse souterraine pour estimer la biomasse du peuplement, la surestimation pouvait atteindre 18% dans notre zone d'etude. Les resultats de notre etude justifient le developpement d'equations allometriques regionales ameliorees pour des estimations plus precises a l'echelle locale. L'incorporation des variations intraspecifiques des attributs importants, tels que le defilement de la tige des arbres, peut etre particulierement utile. [Traduit par la Redaction] Mots-cles : amenagement ecosystemique, variations intraspecifiques des attributs, rapport racines-tiges, defilement de la tige, densite du bois., Introduction Increasing pressure to reduce net carbon dioxide (CO2) emissions in light of climate change is spurring development of global strategies such as carbon markets that encourage carbon offsets through [...]

The first issue of the Canadian Journal of Forest Research (CJFR) was published in March 1971 by the National Research Council of Canada with J.L. Farrar, Faculty of Forestry at [...]

Wildfire is the predominant natural disturbance in the boreal forests of western Canada. Natural disturbance based forest management involves the use of retention harvesting to retain stand structural diversity after harvest; however, unlike fire, this partial harvesting technique does not cause combustion of the forest floor. Application of prescribed burning to areas treated with retention harvesting might emulate the influence of wildfires more effectively than harvesting alone. We compared understory vascular plant diversity, abundance, and composition between forest stands subjected to dispersed retention harvesting (10% retention) with and without prescribed burning 1, 6, and 11 or 12 years after burning. Untreated forest was included as a reference. Research was conducted in conifer-dominated, mixedwood, and deciduous-dominated boreal forest stands in northwestern Alberta, Canada. In deciduous-dominated stands, burned areas of retention harvested stands had higher species richness and greater cover than did unburned areas. In all three forest cover types, effects of harvest with and without burn on species richness, cover, and composition were still evident a decade after disturbance. Fire-adapted species benefited most from the prescribed burn treatment. The combination of prescribed burning with retention harvesting can be considered a useful option in forest management that aims to emulate natural disturbance. Key words: prescribed burning, retention harvesting, fire, understory vascular plants, boreal forest. Les perturbations qui dominent dans les forets boreales de l'ouest du Canada sont causees par les feux de foret. L'amenagement forestier qui s'inspire des perturbations naturelles inclut l'utilisation de la coupe avec retention pour conserver la diversite structurale a la suite de la recolte. Cependant, cette methode de coupe partielle n'entraine pas la combustion de la couverture morte comme c'est le cas avec le feu. Le recours au brulage dirige dans les zones soumises a une coupe avec retention pourrait imiter l'effet des feux de foret plus efficacement que la coupe seule. Nous avons compare la composition, l'abondance et la diversite des plantes vasculaires en sous-etage dans des peuplements forestiers soumis a une coupe avec retention des arbres disperses (10 % de retention) avec et sans brulage dirige 1, 6 et 11 ou 12 ans apres le brulage. Une foret non traitee a ete incluse comme reference. Cette etude a ete realisee dans le nord-ouest de l'Alberta, au Canada, dans des peuplements de foret boreale domines soit par des resineux soit par des feuillus et dans des peuplements mixtes. Dans les peuplements domines par des feuillus soumis a une coupe avec retention, la richesse en especes et la couverture etaient plus grandes dans les zones brulees que dans les zones non brulees. Dans les trois types de couvert forestier, les effets de la recolte avec et sans brulage sur la richesse en especes, la couverture et la composition etaient encore evidents 10 ans apres la perturbation. Les especes adaptees au feu ont le plus beneficie du brulage dirige. La combinaison du brulage dirige et de la coupe avec retention peut etre consideree comme une option utile pour l'amenagement forestier qui cherche a imiter les perturbations naturelles. [Traduit par la Redaction] Mots-cles: brulage dirige, coupe avec retention, feu, sous-etage, plantes vasculaires, foret boreale., Introduction Wildfire is the predominant stand-replacing natural disturbance in the boreal forest and it drives the region's vegetation dynamics (Johnson 1992; Payette 1992). The understory vegetation layer hosts most of [...]

The spatial effects of vegetation control on early tree growth were investigated in central Alberta, Canada, for four years after the establishment of hybrid poplar plantations including the two clones Walker (Populus deltoides x (P. laurifolia x P. nigra)) and its progeny Okanese (Walker x (P. laurifolia x P. nigra)). Tree survival and growth, herbaceous vegetation cover, soil nutrient availability, moisture, temperature, and light availability were assessed. Tree growth in the first two years after establishment was improved through selective in-row vegetation control close (within 50 cm) to trees for both aboveground (mechanical) and above- and below-ground (chemical) control. This was associated with increased light availability for trees. In contrast, growth in the third and fourth years benefitted from control of aboveground vegetation within 140 cm of the stem, and this was associated with increased nutrient availability. These findings suggest that the effects of neighbouring vegetation on trees shift from aboveground competition near the tree stem to belowground competition further (>50 cm) away; thus between-row vegetation control is more important starting in the third year after establishment. Okanese outperformed Walker poplar across all treatments and was more responsive to vegetation control, reflecting its superior performance, higher plasticity, and greater potential for short-rotation intensive-culture plantations. Key words: hybrid poplar, tree growth, aboveground and belowground competition, resource availability, vegetation management. Les effets de nature spatiale de la maitrise de la vegetation sur la croissance precoce des arbres ont ete etudies dans le centre de l'Alberta, au Canada, pendant quatre ans suivant l'etablissement de plantations de peupliers hybrides incluant les deux clones Walker (Populus deltoides x (P. laurifolia x P. nigra)) et sa descendance Okanese (Walker x (P. laurifolia x P. nigra)). La survie et la croissance des arbres, le couvert de vegetation herbacee, la disponibilite des nutriments dans le sol, l'humidite, la temperature, et la disponibilite de la lumiere ont ete evalues. Durant les deux premieres annees suivant l'etablissement, la croissance des arbres a ete amelioree par la maitrise selective de la vegetation dans les rangs pres (a moins de 50 cm) des arbres tant dans le cas de la maitrise aerienne (mecanique) qu'aerienne et souterraine (chimique). Cela etait associe a plus grande disponibilite de la lumiere pour les arbres. Par contre, durant les troisieme et quatrieme annees la croissance a beneficie de la maitrise aerienne de la vegetation en dedans de 140 cm de la tige et cela etait associe a une plus grande disponibilite des nutriments. Ces resultats indiquent que les effets de la vegetation avoisinante passent de la competition aerienne pres du tronc des arbres a la competition souterraine plus loin (>50 cm). Par consequent, la maitrise de la vegetation entre les rangs est plus importante a partir de la troisieme annee suivant l'etablissement. Le clone Okanese a ete plus performant que le clone Walker peu importe le traitement et reagissait mieux a la maitrise de la vegetation, refletant sa performance superieure, sa plus grande plasticite et son potentiel plus eleve pour les plantations a culture intensive et courte rotation. [Traduit par la Redaction] Mots-cles: peuplier hybride, croissance des arbres, competition aerienne et souterraine, disponibilite des ressources, gestion de la vegetation., Introduction Plantations of fast-growing hybrid poplar trees play a significant role in wood and fibre production and as a supplier of biomass for energy, alternative fodder sources, and ecosystem services [...]

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 [...]

Abstract: Distylous species typically experience self-incompatibility with one morph often having partial selfcompatibility Small populations may therefore experience greater rates of selfing/intramorph crosses leading to skewed morph ratios and reduced [...]

: Terrestrial gastropods are important decomposers, herbivores, and prey items in forest systems and constitute a poorly understood element of forest biodiversity in Canada. We sampled terrestrial gastropod assemblages in northwestern Alberta, Canada, using board traps and forest floor sampling to examine their association with forest composition, structure, and environment (forest floor depth and moisture, coarse woody debris, understory vegetation cover) in four boreal mixedwood cover types: broadleaf (deciduous) dominated (DDOM), broadleaf (deciduous) dominated with coniferous understory (DDOMU), mixed conifer and broadleaf (MX), and conifer dominated (CDOM). The highest total gastropod abundance and richness occurred in the DDOM cover type. Furthermore, DDOM assemblages accumulated species more quickly (with sampling effort) and supported more gastropod species at higher levels of dominance than found in other cover types. The mix of coniferous and broadleaved trees influenced gastropod distributions within stands; however, associations observed between gastropod species and tree species differed among cover types, suggesting complex ecological contingency. For example, conifer basal area was an important driver of gastropod assemblage in DDOM and DDOMU forests, whereas broadleaf basal area was the most important driver in the CDOM forest type. We conclude that tree species mixture at a variety of scales sustains diversity of gastropod assemblages and that this understanding is significant for conservation of this taxon on mixedwood boreal forest landscapes. Key words: biodiversity, boreal forest, forest composition, gastropod assemblage, species dominance, gastropod sampling, Gastropoda, Pulmonata. Resume: Les gasteropodes terrestres sont d'importants decomposeurs, herbivores et proies dans les systemes forestiers et constituent un element peu connus de la biodiversite forestiere au Canada. Nous avons echantillonne les assemblages de gasteropodes terrestres dans le nord-ouest de l'Alberta, au Canada, en utilisant des pieges et l'echantillonnage de la couverture morte pour etudier leur association avec la composition, la structure et l'environnement de la foret (epaisseur et teneur en eau de la couverture morte, debris ligneux grossiers, couvert vegetal du sous-bois) dans quatre types de couvert forestier en foret boreale mixte: domine par les feuillus (DF), domine par les feuillus avec un sous-etage de coniferes (DFSEC), melange de coniferes et de feuillus (MCF) et domine par les coniferes (DC). L'abondance et la richesse les plus elevees de gasteropodes ont ete observees dans le type de couvert DF. De plus, les assemblages sous un couvert DF accumulaient les especes plus rapidement (avec l'effort d'echantillonnage) et supportaient plus d'especes de gasteropodes a des degres plus eleves de dominance que dans les autres types de couvert forestier. Le melange de coniferes et de feuillus influencait la repartition des gasteropodes dans les peuplements; cependant, les associations observees entre les especes de gasteropode et les especes d'arbre etaient differentes selon le type de couvert forestier, ce qui suppose une eventualite ecologique complexe. A titre d'exemple, la surface terriere des coniferes etait un facteur determinant pour les assemblages de gasteropodes dans les types de couvert forestier DF et DFSEC tandis que la surface terriere des feuillus etait le facteur le plus important dans le type de couvert forestier DC. Nous concluons que le melange des especes d'arbre a diverses echelles supporte la diversite des assemblages de gasteropodes et qu'il est important de compren-dre cela pour la conservation de ce taxon dans les paysages de foret boreale mixte. [Traduit par la Redaction] Mots-cles: biodiversite, foret boreale, composition forestiere, assemblage de gasteropodes, dominance des especes, echantillon-nage des gasteropodes, Gastropoda, Pulmonata., Introduction The boreal mixedwood forest is an intricate patchwork of broadleaved and coniferous trees produced and maintained by the local balance of disturbance events and successional development (Chen and Popadiouk [...]

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 [...]

Increasing environmental concerns with forestry have led to mounting interest in mixedwood management as a possible strategy to achieve a diversity of ecological and productivity goals within the context of sustainable forest management. This review focuses on the effects of mixedwoods on biodiversity including understory plants, birds, soil fauna, and ectomycorrhizae (ECM). It examines stand-level species diversity and composition but particularly focuses on the regional scale (gamma diversity) by examining evidence for the occurrence of mixedwood-indicator species. The main conclusions are as follows: (i) The existence of different tree species in the canopy is associated with provision of a greater diversity of microhabitats allowing for the addition of understory plant species associated with each canopy species. However, there is little evidence for the existence of understory plant species uniquely associated with mixedwoods. (ii) Some bird species require or prefer the presence of different tree species within a landscape or within a stand. Mixed forest stands and landscapes are thus critical to support populations of these species. (iii) A few studies showed a positive effect of mixed stands or mixed litters on some groups of soil organisms, but high variability makes it difficult to draw firm conclusions about any potential benefits of mixedwoods for biodiversity of soil fauna. (iv) Some ECM taxa are associated with multiple hosts, and could thus benefit from availability of multiple possible host species found in mixed forest stands. Several studies confirmed that there was a greater abundance of multiple-host ECM taxa in mixedwoods. Key words: mixedwoods, gamma diversity, understory vegetation, birds, soil fauna, ectomycorrhizae. Les preoccupations environnementales croissantes en foresterie ont provoque un interet pour l'amenagement mixte comme une strategie possible dans un contexte d'amenagement forestier durable. Cette revue de litterature se concentre sur les effets des peuplements mixtes sur la biodiversite, incluant les plantes de sous-bois, la faune aviaire, la faune du sol, et les ectomycorrhizes (ECM). Elle examine la diversite et la composition specifiques a l'echelle des peuplements mais focalise particulierement sur l'echelle du paysage (diversite gamma) en recherchant la presence d'especes indicatrices des peuplements mixtes. Les principales conclusions sont les suivantes : (i)L'existence de differentes especes d'arbres dans la canopee est associee avec une plus grande diversite de microhabitats, permettant l'addition des especes de plantes de sous-bois associees a chacune des especes de la canopee. Il n'y a toutefois que peu d'indications quant a l'existence d'especes de plantes de sous-bois associees exclusivement aux peuplements mixtes. (ii) Certaines especes d'oiseaux exigent ou preferent la presence de differentes especes d'arbres dans un paysage ou un peuplement. Les peuplements ou paysages forestiers mixtes sont donc critiques pour la conservation de telles especes. (iii) Quelques etudes ont montre un effet positif des peuplements ou litieres melanges sur certains groupes d'organismes du sol, mais la forte variabilite de ces resultats rend toute conclusion hasardeuse. (iv) Certains taxa d'ECM sont associes a des hotes multiples, et pourraient donc beneficier de la disponibilite de plusieurs hotes dans les peuplements mixtes. Plusieurs etudes ont confirme la plus grande abondance de ces taxa a hotes multiples dans les peuplements mixtes. Mots-cles : peuplements mixtes, diversite gamma, vegetation du sous-bois, faune aviaire, faune du sol, ectomycorrhizes., 1. Introduction 1.1. Mixedwoods Canopy trees play a central role in forest ecosystem processes such as net primary productivity, hydrology and nutrient cycling. They also moderate the forest microclimate and [...]

We explored interactions among plant growth forms in the understory of mature boreal mixedwood forests in western Canada by investigating the competitive influence of erect shrubs on herbs (forbs and grasses). We established 10 pairs of plots; all erect shrubs were removed in one plot of each pair (removals) and left intact in the other plot (controls). Two years later, we harvested all aboveground biomass of the herbaceous layer (herb biomass: this included graminoids, forbs, trailing shrubs, and species with a woody base but not woody stems) from the 20 plots. We tested for significant differences in understory species biomass and composition between control and removal plots and examined the influence of 25 environmental factors on species composition of the herbaceous layer. Competition intensity was measured by the natural logarithm of response ratio (In RR) index based on herb biomass. After erect shrub removal, there was a significant increase in herb biomass, mostly due to an increase of the most common species (e.g.. Cornus canadensis Linnaeus, Linnaea borealis Linnaeus). The values of competition intensity (In RR) varied among herb species but were, overall, positive, indicating a release from competition following shrub removal. Composition of the herbaceous layer was significantly different between removal and control plots and was also significantly related to seven environmental factors, which explained 40% of the variation in composition. Our study suggests that there is asymmetric competition for light between erect shrub and herb species in boreal ecosystems. Key words: removal experiment, functional diversity, understory community, species interactions, dominant species, boreal forest. Les auteurs ont etudie les interactions entre les formes de croissance des plantes en sous etage de forets boreales mixtes matures dans l'ouest du Canada, en examinant l'influence competitive des arbustes dresses et des herbacees. Ils ont etabli 10 paires de parcelles, supprimant tons les arbustes dresses dans une parcelle de chaque paire (supprimes) et en laissant intacte l'autre parcelle (temoins). Deux ans plus tard, ils ont recolte toute la biomasse epigee de la strate herbacee (biomasse herbacee; incluant les plantes gramineennes et non-gramineennes, les arbustes rampants et les especes munies d'une base ligneuse mais sans tige ligneuse) des 20 parcelles. Ils ont effectue des lests de differences significatives pour la biomasse des especes de sous etage et la composition entre les parcelles temoins et de suppression, pour examiner l'influence de 25 facteurs environnementaux sur la composition en especes de la strate herbacee. Ils ont mesure l'intensite de la competition par le log du Rapport de Reaction (In RR), un index base sur la biomasse herbacee. Suite a la suppression des arbustes dresses, on observe une augmentation significative de la biomasse herbacee, due en grande partie a une augmentation des especes les plus communes (e.g. Cornus canadensis Linnaeus, Linnaea borealis Linnaeus). La valeur de l'intensite de la competition (In RR) varie entre les especes herbacees, mais demeure dans l'ensemble positive, ce qui indique une liberation de la competition suite a l'enlevement des arbustes. La composition de la strate herbacee s'avere significativement differente, entre les parcelles avec suppression et temoins, et montre egalement une relation significative avec sept facteurs environnementaux, lesquels expliquent 40 % de la variation de la composition. Les resultats suggerent l'existence d'une competition asymetrique pour la lumiere entre les especes arbustives dressees et herbacees, dans les ecosystemes boreaux. Mois-cles : experience d'elimination, diversite fonctionnelle, communaute de sous etage, interactions interspecifiques, especes dominantes, foret boreale. [Traduit par la Redaction], Introduction Interactions among plant species play an important role in regulating composition of local communities and ecosystems (Brooker 2006) and in mediating ecosystem functioning when a given species or functional [...]

Epiphytic mosses and liverworts contribute substantially to the bryophyte diversity of circumpolar boreal forests but are susceptible lo altered growing conditions after forest harvesting. Management practices that retain some trees after harvest may enhance epiphyte survival; however, the effectiveness or this emerging method needs lo be assessed. We examined the survival, composition, and nearest neighbour relationships of epiphytic bryophytes on trembling aspen (Populus tremuloides Michx.) across a range (10%-100%) of dispersed green-tree retention 5 years after harvest in boreal mixed- wood forest. Growth of the forest floor moss Hylocomium splendens (Hedw.) Schimp. in B.S.G. was used as an indicator of changes in moisture availability for epiphytes following harvesting. Epiphyte richness and abundance increased with canopy retention and were positively correlated with local abundance of coniferous trees. Positive associations among neighbouring species in intact forest demonstrated that interspecies relationships form naturally. However, there was a shift in species composition after harvesting and fewer interspecific associations with declining retention. These trends were accompanied by reduced Hylocomium splendens growth, which implies that moisture may be an important driver of epiphyte response. Although different levels of canopy retention were similarly capable of maintaining some epiphytes, the loss of species associated with intact forest will require consideration of alternative management practices for their conservation. Key words: corticolous, Hylocomium splendens, liverwort, moss, poikilohydric. variable retention. Les mousses et les hepatiques epiphytes contribuent subsiantiellement a la diversite des bryophytes des forets boreales circumpolaires, mais sont sensibles aux modifications des conditions de croissance, suite aux operations forestieres. Les methodes d'amenagement qui conservent certains arbres apres la recolte peuvent ameliorer la survie des epiphytes; cependant, on doit evaluer l'efficacite de ces methodes en emergence. Les auteurs ont examine la survie, la composition et les relations avec les voisins les plus rapproches des bryophytes epiphytes sur le peuplier faux-tremble (Populas tremuloides Michx.) pour l'ensemble d'une aire (10% a 100%) comportant des arbres vivants conserves et disperses, 5 ans apres la recolte dans une foret boreale mixte. Ils ont utilise la croissance d'une mousse du parterre forestier, l'Hylocomium splendens (Hedw.) Schimp, in B.S.G., colome indicatrice des modifications de la disponibilite de l'humidite pour les epiphytes, suite a la recolte des arbres. La richesse et l'abondance des epiphytes augmentent avec la retention de la canopee et montrent des correlations positives avec l'abondance localisee de coniferes. Les associations positives avec les especes avoisinantes dans la foret intacie demontrent que des relations interspecifiques se forment nalurellement. Cependant, on observe un deplacement de la composition en especes apres la recolte et moins d'associations interspecifiques avec une diminution de la retention. Ces tendances s'accompagnent d'une reduction de la croissance de l'Hylocomium splendens, ce qui implique que l'humidite pourrait etre un agent causal important de la reaction des epiphytes. Bien que differents degres de conservation de la canopee peuvent etre egalement aptes a maintenir certaines epiphytes, la perte d'especes associees aux forets intactes necessitera la definition de methodes alternatives d'amenagement pour leur conservation. Mots-cles: corticole, Hylocomium splendens, hepatiques, mousse, poikilohydrique, retention variable. [Traduit par la Redaction], Introduction Forest management practices that retain a greater volume of standing trees after harvest are gradually becoming more widely accepted in place of traditional clearcut methods in North American and [...]

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 [...]

In mixedwood boreal forests of western Canada, stands classified as 'pure deciduous' by forest inventories sometimes contain a few large white spruce (Picea glauca (Moench) Voss) trees among or emerging from the canopy. These trees are important as regeneration seed sources and for habitat structure. Neither their abundance nor the characteristics of stands in which they occur have previously been quantified. Of 275 'pure aspen' stands in northeastern Alberta, 19.6% contained at least one such spruce detectable in an aerial photograph. These trees were found in stands across the range of sampled canopy heights, densities, age classes, and stand sizes and were often present in the interior of stands, not just on the perimeter. The frequency of 3 ha cells containing at least one spruce was related to (i) stand shape and size, (ii) amount of mature white spruce in adjacent forest, (iii) canopy height, (iv) stand age, and (v) stand density. We conclude that such trees are relatively abundant and widely distributed within the boreal mixedwood forests of Alberta. There is presently no provision to maintain this landscape element within managed forests. More information is needed to determine if or how they should be considered in forest management planning. Dans la foret boreale mixte de l'Ouest canadien, il arrive que les peuplements classes comme << feuillus purs >> dans les inventories forestiers contiennent quelques grosses tiges d'epinette blanche (Picea glauca (Moench) Voss) qui font partie ou emergent de la canopee. Ces arbres sont importants comme source de graines pour la regeneration et pour la structure de (habitat. Toutefois, leur abundance et les caracteristiques des peuplements dans lesquels ils sont presents n'ont jamais ete quantifiees. Parmi 275 << peupleraies pures >> du nord-est de (Alberta, 19,6 % contenaient au moms une telle epinette detectable a partir de photographies aeriennes. Ces arbres ont ete detectes dans des peuplements couvrant toute la gamme de hauteurs de canopee, de densites, de classes d'age et de tailles de peuplement echantillonnees; ils etaient souvent presents a finterieur des peuplements et non seulement en peripherie. La frequence des cellules de 3 ha a contenant au moms une epinette a ete reliee a (i) la forme et la taille du peuplement, (ii) la quantite d'epinettes blanches matures dans la foret adjacente, (iii) la hauteur de la canopee, (iv) Page du peuplement et (v) la density du peuplement. Nous concluons que de tels arbres sont relativement abondants et largement distrbbues dans la foret boreale mixte de l'Alberta. Il n'y a presentement aucune mesure visant a maintenir cet element du paysage dans les foress amenagees. Plus de renseignements sont necessaires pour determiner si ou comment ces arbres devraient etre consideres dans la planification de l'amenagement forestier. [Traduit par la Redaction], Introduction In the boreal mixedwood forests of western Canada, the canopies of upland mesic sites are dominated by some combination of Populus species (typically trembling aspen, Populus tremuloides Michx., but [...]

Abstract: We characterized the ectomycorrhizae (ECM) of planted white spruce (Picea glauca (Moench) Voss) seedlings as affected by mechanical site preparation (MSP) of clear-cut conifer-dominated boreal mixedwood forest. Relative abundance, [...]

We compared understory vegetation composition and richness in aspen-dominated boreal mixedwood forest stands in Alberta, Canada, that had been burned by wildfire with those that burned and were subsequently salvage logged. Stands were examined at early and midsuccessional (2 and 34 years after disturbance(s), respectively) developmental stages. In comparison with wildfire stands, understory communities of early successional salvage-logged stands were characterized by greater species richness, weedy species presence, higher shrub abundance, and lower abundances of fire- specialist seed bank species. In constrained ordination, the understory community of early successional wildfire stands was related to greater canopy cover, sapling density, and moss depth, whereas that of salvage- logged stands was related to greater light, volume of downed deadwood, and litter and organic matter. Longer term effects of salvage logging on the understory community were minimal and, instead, reflected the influence of forest canopy redevelopment. In midsuccessional stands, understory composition was related to conifer density, litter cover, soil moisture, organic layer depth, tall shrub density, and bryophyte-covered microsite cover. Postfire salvage logging can have substantial short- term effects on the postfire understory plant community; in the longer term, effects will depend to a large extent on the influence of harvesting and subsequent management on canopy redevelopment. Nous avons compare la composition et la richesse de la vegetation en sous-etage dans des peuplements de foret boreale mixte domines par le peuplier faux-tremble en Alberta, au Canada, qui avaient et. [Traduit par la Redaction], Introduction Early postfire forest stands are characterized by a distinctive combination of environmental and stand attributes that influence the initial establishment phase of the plant community and have important long-term [...]

Abstract: We compared prefire and postfire organic-layer depths in boreal forest types (14 fires) across Canada, and examined tree recruitment as a function of depth. There was extensive within-stand variation [...]

Abstract: This study assessed the dynamics of gap development in postharvest regeneration in five stands in northwestern Alberta dominated by trembling aspen (Populus tremuloides Michx.). The pattern of gap development [...]

Abstract: The timing of white spruce regeneration in aspen (Populus tremuloides Michx.)--white spruce (Picea glauca (Moench) Voss) boreal mixedwood stands is an important factor in stand development. We examined boreal [...]

We used the mast-seeding tree Picea glauca (white spruce) to examine whether the timing of mast years relative to fire had a lasting effect on the density and timing of regeneration. We studied 17 fires that occurred in mast years and in years with low cone production between 1941 and 1994. Trees were carefully aged by crossdating procedures. Over the 59-yr period studied, there was significantly more regeneration after fires that occurred in mast years than after fires that occurred in years of low cone production. Spruce density was significantly lower after fires that occurred 1-3 years before a mast year than after fires during mast years. The cohort of trees that regenerated in the first mast year after a fire was critical to white spruce regeneration for fires that occurred 0-1 year before a mast year, but mast years occurring three or more years after a fire contributed few recruits. Our results suggest that masting is a key process that interacts with fire to shape stand composition in boreal mixedwoods. For species like white spruce, for which establishment is linked to disturbance, masting may have a contingent, historical effect on succession and landscape structure. Key words: cohorts; crossdating; fire; masting; mixedwood forest; Picea glauca; regeneration; seedbed; white spruce.

1 We used tree ring analysis to determine stem radius and thus examine size variation over time in two even-aged (approximately 40-year-old) mixed populations of black spruce and tamarack established on peatlands in a boreal forest. We also followed the response of one of these populations to improved edaphic conditions over 8 years following drainage. 2 Populations of trees in undrained areas showed a decline in size variability over time until age 20-25 years, after which size heterogeneity was relatively stable. 3 For trees in undrained areas there was a relationship between age and size for the first 20-25 years, but this relationship then broke down due to a period where relative growth rate and size were inversely related. 4 For the population of trees in the drained area, smaller trees (i.e. those that had been growing more slowly prior to drainage) showed significantly greater drainage-induced release growth, while larger trees (those growing faster prior to drainage) showed an initial reduction in growth following drainage and, overall, less release growth. 5 The response of tamarack to drainage was more dramatic than for black spruce. 6 Despite extensive variation in tree size, drainage dramatically reduced variability in growth rate among trees of each species, such that size variability in the populations declined. 7 We postulate that the heterogeneity of microsites with respect to edaphic conditions, perhaps associated with the hummock to hollow microtopographic gradient, has a major influence on growth variation, and hence size inequality, in peatland populations of black spruce and tamarack. Keywords: competition, forest heterogeneity, microsite, peatland, relative growth rate, size variability

Genetic variation was examined by electrophoresis in 14 populations of Stellaria arenicola, an endemic of the Athabasca sand dunes in northern Saskatchewan, Canada, and seven populations of S. longipes, its progenitor. Three of the S. longipes populations were sympatric with the endemic. Populations of the endemic were found to have fewer alleles per polymorphic locus (2.21 vs. 2.37), fewer polymorphic loci (29.9 vs. 33.8), and lower genetic diversity (0.087 vs. 0.107) than populations of the progenitor. Genetic identities for all pairs of populations were high (0.932 to 1.000). The endemic had one novel allele and shared ten alleles with progenitor populations from the sand dunes that were not found in other populations of S. longipes. Populations of both species were found to partition most of their genetic variation within populations. An investigation of the multilocus outcrossing rates revealed that S. arenicola had higher rates of selfing and biparental inbreeding than S. longipes. This study suggests that partial genetic isolation through a shift in the breeding system, in addition to previously reported strong directional selection, has been important in the sympatric evolution of the endemic S. arenicola. The close genetic relationship between populations of S. arenicola and S. longipes found on the Athabasca sand dunes supports the suggestion that the endemic evolved while sympatric to the gene pool of the progenitor species that is found presently in the region.

1 A glasshouse experiment was conducted in which individuals of the rhizomatous grass Calamagrostis canadensis were grown in soil-filled wooden boxes. Directly adjacent to each plant on one side was a control area (same conditions as those in which the plant was growing), while immediately adjacent on the other side was an area with one of the experimental conditions ('shade', 'cool soil', 'cool soil + shade', or 'cool soil + intraspecific competition'). Rhizomes of each plant were allowed the opportunity to grow simultaneously into both the control and the treated side. 2 Fewer rhizomes grew into the 'cool soil + competition' area compared to the number of rhizomes from the same plant growing into the control side and those that did were shorter, showed less branching, had shorter internodes, and produced fewer shoots. Rhizomes entering the 'cool soil' area (with or without shade) showed reduced growth compared to rhizomes from the same individual which grew into the control side. 3 Calamagrostis canadensis appears to display an 'opportunistic guerrilla' strategy of clonal foraging. Provided with the opportunity to 'choose' between different microhabitats for clonal expansion, plants showed preferential entry into, and exploitation of, favourable microhabitats (i.e. warm soil, unshaded, free of competition). 4 For individuals faced with considerable environmental heterogeneity, plasticity of rhizome growth and development allows for greater exploitation of more favourable microhabitats. This may play an important role in the persistence of this species in a variety of boreal forest habitats.

Calamagrostis canadensis (a rhizomatous grass) exists in temperate forest sites of different successional age. It can rapidly colonize disturbed sites to form dense swards. We examined allozyme variation in: four populations (mature forest, intermediate aged forest, forest cutblock, wetland); nine small plots (2 m X 4 m) within the cutblock; and progency of several families from three populations; in order to assess the mode of colonization of disturbed areas and the effect of successional changes on population genetic structure. All four populations showed equal and extensive genetic variation (1.5 to 1.7 alleles per locus [K], 41.7% to 50% polymorphic loci [PPH], [H.sub.st] = 0.155 to 0.208) and were not genetically differentiated ([G.sub.st] = 0.0193, I = 0.986 to 0.997). The cutblock subpopulations also showed considerable genetic variation (K = 1.6 to 1.8, PPL = 50% to 58.3%, [H.sub.st] = 0.151 to 0.278) and no microdifferentiation ([G.sub.st] = 0.034, I = 0.967 to 0.997). We found 14 different genotypes among the 30 individuals sampled from the cutblock as a whole (based on five polymorphic loci). The cutblock subpopulations had from nine to 14 different genotypes each (same five loci, 18 individuals per subpopulation). Seed produced was primarily outcrossed (multilocus estimate 0.888 to 0.900). We concluded that disturbed sites are colonized primarily by sexually produced seedlings. Potential genetic drift and natural selection, which occur during subsequent successional changes, do not result in reduced genetic variation or population differentiation.

The maintenance of species diversity is becoming a key component of sustainable forest management. In the boreal mixedwood of northern Alberta, conifer dominated stands over one hundred years old are among those most threatened under present harvesting regimes. These stands are also important habitat for many bryophyte species. Wise management requires an understanding of the mechanisms controlling bryophyte species richness and evenness in order to either facilitate the identification of species rich areas or to improve the bryophyte habitat in managed stands. This study examines the relationship between microclimate and substrate availability, and bryophyte species richness and evenness at different scales. I sampled bryophyte species occurrence and abundance at three scales: the stand (10 ha), the mesosite (25 X 25 m plots to capture within stand variation), and the microsite (structural elements of the boreal forest providing unique substrates for moss colonization). Percent full sun, PPFD (Photosynthetic Photon Flux Density), soil moisture and pH, vascular plant species richness, microtopography and area of available substrate were measured to estimate inter-mesosite variability. Microsite variability was estimated using a relative measure of mean exponential temperature in combination with descriptive classes of substrate quality. Sampled microsites consisted of 74 stumps, 88 logs, 90 trees, 90 patches of undisturbed soil and 33 patches of disturbed soil. Light and temperature were more variable within stands than between stands (57% and 19 % of the variation respectively), while soil moisture and pH were more variable at the stand level (72% and 30% of the variation respectively). The stand with the greatest species richness had the greatest vascular plant species richness, as well as the highest soil moisture and pH. Bryophyte species richness and evenness is related to variability in forest structure and environment both within and between stands.

Population differentiation for phenotypic plasticity of 12 morphological and reproductive traits was investigated in five populations of the Stellaria longipes complex including a population of the sand dune endemic S. arenicola. Population differentiation was detected for the mean (genotypic) value, amount of plasticity, and pattern of plasticity of traits. Average amount of plasticity was not related to degree of isozyme variability in the populations. Differentiation for pattern of plasticity was much more common than for amount. The direction and extent of divergence among populations was dependent on which of the three trait aspects was under consideration (mean, amount of plasticity, pattern of plasticity) and did not reflect their similarity as revealed by enzyme electrophoretic data. It was concluded that trait means, amounts of plasticity, and patterns of plasticity are independent of one another during evolutionary divergence and may be influenced by mosaic selection.

In the western boreal mixed-wood forest white spruce naturally regenerates quite readily following fire but artificial regeneration after timber harvesting may be difficult to achieve. We are investigating the timing, spatial distribution, and environmental conditions associated with successful and unsuccessful post-fire white spruce regeneration using an hierarchical scale approach. Presence, density and performance of white spruce seedlings were examined in relation to microhabitat (soil temperature, soil N and P availability, soil microbial activity, organic matter, and cover of: shrubs, herbs, nonvascular plants, litter, downed coarse woody material, canopy) and mesohabitat (remaining live trees, snags, slope, aspect, adjacency to residual live spruce) in 14-year-old, 6-year-old and one-year-old burns. Very few seedlings were found at the beginning of the growing season in the 1-year-old burns but many germinated during the summer. In the older burns discriminant analysis showed, at the microhabitat scale, significant differences between plots occupied by white spruce seedlings versus unoccupied plots. In the 6-year-old burn occupied plots had greater moss, lichen, herb and shrub cover, less coarse woody material, and were on steeper slopes. In the 14-year-old burn occupied plots were characterized by more canopy cover, more lichen, herb and litter cover and warmer surface soil temperatures.

Riparian forests are becoming more important for wildlife as buffer zones around lakes become the principle unharvested areas within a harvested landscape in northern Alberta. Changes in forest structure and composition across the riparian forest ecotone were investigated to elucidate patterns along the lakeshore edge-to-interior gradient. Trees, coarse woody material, saplings, shrubs and herbaceous plant species composition were sampled along 200m transects established perpendicular to lakeshore forest edges. Lakeshore forest edges were more structurally diverse with increased coarse woody material, more saplings and mid-canopy trees, and taller saplings than further into the forest. Individual herb and shrub species exhibited different patterns at the lakeshore edge: Rosa acicularis, Viburnum edule, Linnaea borealis and Mitella nuda increased along the edge-to-interior gradient, while Amelanchier alnifolia, Petasites palmatus and Lathyrus ochroleucus decreased. Edge effects appear to penetrate 50m into the forest. Data also illustrate considerable heterogeneity within the interior forest, as well as at the lakeshore forest edge. Structural and compositional features of the lakeshore forest edge may be important to wildlife The variation in forest structure and composition due to edge effects in riparian forests is an important part of the overall heterogeneity in the boreal forest landscape.

Riparian forests, those adjacent to open water, are expected to have high productivity and species richness as a result of their topographic position, proximity to water and the influence of relatively strong ecological gradients. They may also serve important ecological roles in the landscape as movement corridors for vertebrates and as a large proportion of the remaining older forest in areas subjected to timber harvesting. We examined the ecological uniqueness of riparian forests in the aspen-dominated boreal mixed-wood forest of Alberta. Using a series of paired transects we compared forest structure and composition 50 m away from the lakeside forest edge with that in the same stand of forest but 600 to 800 m into the interior. The following traits were examined: trees - size, age, density by species, canopy cover; snags - size, condition by species; coarse woody material - amount, size, condition by species; shrub and herb cover to species, litter depth, soil N and P availability. Data were analyzed by paired t-tests and discriminant analysis. Riparian habitats were characterized by more balsam fir and paper birch, less balsam poplar, larger aspen and spruce, greater soil phosphorus availability, a denser canopy and lower species diversity for herbs. The discriminant analysis showed significant differentiation between the two habitat types. Floristic similarity between paired transects showed that 70 - 75% of species were in common.

Whitebark pine (Pinus albicaulis Engel.) is found at timberline throughout the Cascade, Coastal, and Rocky Mountains of North America. Over the past 20 years, whitebark pine has undergone a population decline in Northwestern Montana and Southern Alberta. The combined effects of white pine blister rust (an introduced fungus), mountain pine beetles and fire suppression have been suggested as causes of this deterioration. Information on the extent of blister rust infection, regeneration of this species, and the extent and partitioning of genetic variation was required for the design of an effective conservation strategy. 29 whitebark pine populations were sampled throughout the Canadian Rockies from Waterton Lakes National Park, AB to Mt. Robson Provincial Park. BC. Trees were examined for signs of blister rust, sized and aged, and needle samples were taken for isozyme analysis. Over 30% of all the individuals sampled were infected with blister rust. All sites contained infected individuals. The average age of 29 sites was between 100 and 200 years with some individuals older than 600 years. Some of these sites showed synchronized regeneration suggesting that they were initiated by disturbance. Isozyme analysis is in progress and results will be presented.