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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 [...]

Grasslands are impacted by many disturbances, including energy development. While temporary working platforms using access mats to support large equipment can minimize soil disturbance, less is known about matting impacts on grassland vegetation. We assessed heavy traffic effects on sandy and loamy Mixedgrass Prairie in southeast Alberta, Canada, where traffic occurred in 2015 either directly on grassland or on temporary matting. Vegetation was assessed in 2016 and 2017. Treatments varied in type (with/without matting), timing (spring vs. fall vs. season‐long) and duration (6 vs. 12 weeks, and 24 weeks for season‐long) of occurrence. While grass biomass was unaffected by direct wheeled traffic, native forb biomass declined, particularly during the first growing season; 1 year later, plots with prior long‐term matting had more native forbs. Where traffic occurred on mats, grass biomass decreased when mats were placed for 6 or 12 weeks in spring, or for the entire growing season. Longer mat use also increased introduced forbs, which were positively associated with soil nitrogen supply rates. Plant biomass changes from matting (less grass, more introduced forbs) were more apparent in loamy‐sand than loam soils. Overall, while direct traffic had limited impacts on vegetation, matting was more likely to alter vegetation, particularly when placed in spring or for longer periods, and further varied with ecosite type and the timing of traffic disturbance. We recommend that access mats be limited to placement for short periods (≤12 weeks), preferably in falling, to conserve mixedgrass prairie, while longer placement intervals be avoided. [ABSTRACT FROM AUTHOR]

The impact of summer cattle grazing on deciduous tree regeneration within uncut forests, clearcuts, partially harvested areas, and in-block haul road habitats was examined in four experimental pastures of central Alberta during 2008 and 2009. Sampling of 233 field plots, both inside and outside cattle exclosures, was used to document sapling densities, height, and type of damage. Tree densities (primarily aspen (Populus tremuloides Michx.)) differed among habitats but less so with exposure to cattle. Densities were greatest in clearcuts, followed by partially harvested areas and then uncut forest and haul roads. While exposure to cattle reduced total tree regeneration, sapling densities and sizes remained sufficient to meet postharvest standards for deciduous forest regeneration in Alberta, even with exposure to cattle. Cattle damage in harvested areas was primarily from browsing (≤ 3.2% of saplings), with proportionally more trees affected in uncut forests (8.6%). Browsing was particularly high on balsam poplar (Populus balsamifera L.) (25%) during 2008. Although sapling damage increased with high cattle stocking in 2008 (to 10.5%), total mortality was limited to 15.5% through 2009. These findings show that despite cattle impacts to some saplings, damage levels were insufficient to alter deciduous regeneration, highlighting the compatibility of cattle grazing and sustainable forest management on public lands in this region. Key words: aspen regeneration, cattle stocking rate, tree damage and mortality, habitat type, multiple use. Nous avons etudie l'impact du paturage estival du betail sur la regeneration d'essences feuillues dans des habitats de foret non coupee, de coupe a blanc, de coupe partielle et de voies de trainage, en 2008-2009, dans quatre paturages experimentaux du centre de l'Alberta. L'echantillonnage de 233 parcelles etablies sur le terrain, a l'interieur et a l'exterieur d'exclos a betail, a permis de documenter la densite et la hauteur des gaules ainsi que le type de dommages qu'elles avaient subis. La densite des arbres, principalement du peuplier faux-tremble (Populus tremuloides Michx.), differait selon l'habitat mais dans une moindre mesure lorsque les habitats avaient ete exposes au betail. Les plus fortes densites ont ete observees dans les coupes a blanc, suivies des coupes partielles, puis des forets non coupees et des voies de trainage. Bien que l'exposition au betail ait reduit la regeneration totale, la densite et la taille des gaules sont demeurees assez elevees pour rencontrer les normes albertaines de regeneration de la foret decidue apres coupe, meme apres avoir ete exposee au betail. Les principaux dommages causes par le betail dans les aires de recolte etaient dus au broutage (≤ 3,2% des gaules); proportionnellement plus d'arbres ont ete endommages dans les forets non coupees (8,6%). Le broutage etait particulierement important sur le peuplier baumier (Populus balsamifera L.) (25%) en 2008. Malgre l'augmentation des dommages subis par les gaules (a 10,5%) a cause de la densite elevee du betail en 2008, la mortalite n'a pas depasse 15,5% en 2009. Ces resultats montrent qu'en depit de l'impact du betail sur une certaine quantite de gaules, le niveau de dommages etait insuffisant pour compromettre la regeneration feuillue, mettant en evidence la compatibilite entre le paturage du betail et l'amenagement forestier durable sur les terres publiques dans cette region. [Traduit par la Redaction] Mots-cles : regeneration du peuplier faux-tremble, densite du betail, dommages aux arbres et mortalite, type d'habitat, usages multiples., Introduction Deciduous forests on public land in western Canada are important for supporting multiple uses, including cattle grazing and timber production. Balancing these uses is fundamental to maintaining forest health [...]