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Understory protection harvesting is a form of partial cutting that can be used in aspen (Populus tremuloides Michx.)-dominated stands that have understories of white spruce (Picea glauca (Moench) Voss). This practice involves removing 75% to 85% of the merchantable aspen while minimizing damage to the advance spruce regeneration, in addition to leaving 15% to 25% of the aspen standing to reduce potential windthrow of the spruce understory. In this paper, we summarize results from 18 stands measured 10 to 12 years after understory protection harvest. Diameter growth of spruce increased during the first five years after harvest while height growth increased during the second five-year period (5 to 10 or 7 to 12 years after release). Consistent with other studies, mortality rates of aspen trees ≥7.1 cm DBH (diameter breast height, 1.3 m) averaged 45.0% over the 10–12 year period following harvesting. Spruce mortality averaged 27.5% over the same 10–12 year period. Substantial aspen regeneration was evident across most harvested blocks, with aspen sapling densities 10–12 years from harvest being higher in removal (14,637 stems⋅ha−1) than in buffer areas (6686 stems⋅ha−1) and in extraction trails (7654 stems⋅ha−1). Spruce sapling (>1.3 m height and <4 cm DBH) densities averaged 1140 stems⋅ha−1 in removal areas at ages 10–12, with these trees likely being present as seedlings at the time of harvest. Mixedwood Growth Model projections indicate merchantable volumes averaging 168 m3⋅ha−1 (conifer) and 106 m3⋅ha−1 (deciduous) 70 years from harvest, resulting in MAI (mean annual increment) for this period averaging 2.0 m3⋅ha−1⋅y−1 with MAI for a full 150-year rotation of approximately 2.5 m3⋅ha−1⋅y−1. [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Identifying the main drivers of tree height growth on reclaimed oil sands sites of northern Alberta can provide useful information on what can be done to shorten the recovery time of these disturbed sites. The effect of water availability, foliar nutrient concentrations, competition, and soil chemical properties on young trembling aspen and white spruce height across two soil types (peat-mineral mix and forest floor-mineral mix) and two fertilizer levels (200 kg NPK ha−1 and no fertilizer) was examined. For comparison, we also studied a natural site that burned the same year the reclaimed site was established. On the reclaimed site, peat-mineral soil had the greatest tree height for both species, though not by a significant margin in the case of white spruce. The fertilizer treatment had no apparent effect on tree height on the forest floor-mineral soil and a negative effect on the peat-mineral soil. Fertilization increased vegetation cover on both soil types, which, when combined with the negative or lack of durable effect of fertilization on tree height, suggest that the increase in competition for resources could have had a stronger effect on tree height than the increase in immediately available nutrients following fertilization. The majority of tree height growth drivers found were related to nutrient availability and, as far as we can tell, did not significantly differ between reclamation soil types. Aspen sucker height on the burned site was not strongly correlated to the measured variables, suggesting that suckers do not yet fully rely on their environment for height growth. [ABSTRACT FROM AUTHOR]

Ecological processes driving tree success in the early stages of succession are complex and often poorly understood, involving direct and indirect relationships among multiple agents modulated by legacies. Reclamation areas of open-pit mines provide a unique opportunity to study these relationships, as these sites are often homogeneous and have few ecological legacies. Our study evaluated the early performance of three boreal tree species planted at different densities over a large reclaimed landscape (57 ha) in northern Alberta, Canada, that varied in landscape topography, surface soils, and coarse woody material. A range of soil, topographical, and seedling characteristics were measured over five growing seasons. The two surface soils had stark differences in their physical and chemical properties. Overall, seedling survival was high (> 80%) for jack pine (Pinus banksiana) and white spruce (Picea glauca) and somewhat lower (60%) for trembling aspen (Populus tremuloides). All three species grew taller in the fine-textured than in the coarse-textured soils. Linear models identified simple relationships among some of the monitored variables. To further explore more complex relationships, we built a structural equation model for jack pine growth, 2 and 5 years after planting. On coarse-textured soil, the factors controlling pine growth shifted from intrinsic factors of seedling quality in the second growing season to more complex interactions in the fifth growing season, driven by soil nutrients, water availability and colonizing vegetation. We believe these models have the potential to be useful in forest reclamation, by identifying driving factors that could be monitored to indicate reclamation success. [ABSTRACT FROM AUTHOR]

Density manipulation of overstory aspen provides increased light levels to promote growth of understory spruce, while it may also impact the air and soil temperature. We monitored temperature for three growing seasons in young mixedwood stands of variable density at two boreal locations in Alberta, Canada. Results indicate that partial aspen cover provides frost protection that may be location specific. Mean air temperature was similar or increased slightly across aspen densities during the growing season, while mean soil temperature significantly increased with decreasing overstory cover. The amount of accumulated air and soil heat over the growing season was inversely related to aspen density. The differential impact of density on temperature contributes to variation in growth relationships and may explain regional differences in competition effects. [ABSTRACT FROM AUTHOR]

Fallen logs of trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) at various stages of decomposition were sampled from undisturbed and 1-, 14-, and 28-year-old post-fire and post-harvest sites in northern Alberta and studied for differences in the associated microfungus communities. Wood samples were plated directly onto each of six different media and, from these, fungal species were identified and enumerated over a 24-month period. Approximately 10 000 isolates were obtained, representing 292 species of filamentous microfungi, including 41 ascomycetes, 29 zygomycetes, and 222 mitosporic fungi. The most commonly isolated species were Trichoderma viride (Gray) Pers., Rhinocladiella atrovirens Nannf., Penicillium pinophilum Hedgcock, and Mortierella ramanniana (Moller) Linnem. Cluster analysis and ordination of microfungus communities in logs showed that the tree species of the log had the greatest influence on the species composition of communities. Fungus community composition was also correlated with the stage of decomposition. Species richness was highest in logs from undisturbed sites and lowest in logs from the most recently disturbed sites. Species diversity (Shannon-Weaver) was only slightly higher at undisturbed sites than at disturbed sites. The most significant environmental factor was log moisture, which increased proportionately with stage of decomposition and was significantly correlated with climatic factors.Key words: ecology, fungi, ordination, succession, species richness, diversity.Les auteurs ont échantillonné des troncs morts et gisants de peuplier faux-tremble (Populus tremuloides Michx.) et d'épinette blanche (Picea glauca (Moench) Voss) à divers stades de décomposition, sur des sites non-perturbés, et après 1, 14 et 28 ans depuis un feu ou une récolte, dans le nord de l'Alberta, puis ils en ont étudié les différences au niveau des communautés de microfungi. Des échantillons de bois ont été directement mis en plaque sur six milieux différents et, à partir de ceux-ci les espèces fongiques ont été énumérées, sur une période de 24 mois. On a ainsi obtenu près de 10 000 isolats, représentant 292 espèces de champignons filamenteux, incluant 41 ascomycètes, 29 zygomycètes, et 222 champignons mitosporiques. Les espèces les plus communément isolées sont les Trichoderma viride (Gray) Pers., Rhinocladiella atravirens Nannf., Penicillium pinophilum Hedgcock, et le Mortierella ramanniana (Moller) Linnem. L'analyse par regroupement et ordination des communautés microfongiques dans ces troncs morts montrent que l'espèce d'arbre impliquée influence le plus fortement la composition en espèces des communautés. La composition de la communauté fongique est également corrélée avec les stades de la décomposition. La richesse en espèces est la plus élevée dans les troncs morts de sites non-perturbés, et la plus faible dans les troncs morts des sites les plus récemment perturbés. La diversité en espèces (Shannon-Weaver) n'est que légèrement supérieure sur les sites non-perturbés comparativement aux sites perturbés. Le facteur environnemental le plus significatif est l'humidité de la bille, laquelle augmente proportionnellement avec le stade de décomposition et est significativement corrélée aux facteurs climatiques.Mots clés : écologie, champignons, ordination, succession, richesse en espèces, diversité.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Reports that forest policymakers in Canada are considering the allowable cut effect (ACE) as a potential mechanism to provide tenure holders with incentives to practice enhanced forest management. To investigate the incentives created by the ACE, this paper estimates returns to ACE investments for a trembling aspen (Populus tremuloides Michx.) - white spruce (Picea glauca (Moench) Voss) mixedwood forest in Alberta. A timber supply model is used to optimize harvesting schedules to maximize net present values over a 200-year planning horizon. A number of scenarios are investigated with variations in intensity of silvicultural investments, beginning age-class distributions, levels of flexibility around the allowable annual cut (AAC), calculations of AACs based on coniferous and mixedwood volumes, and green-up constraints. In our simulations, it was difficult to find positive returns to the ACE. Positive returns only occurred when operating under harvesting constraints with a mature starting forest and AAC calculations that ignored deciduous volumes. In those limited cases where there were positive returns to the ACE, returns were higher for extensive, rather than intensive investments. Combining these results with other potential impediments to the ACE, previously identified in the literature, the probability of tenure holders having incentives to undertake ACE investments is low.

A few studies in young mixedwood stands demonstrate that precommercial thinning of aspen at early ages can improve the growth of spruce and increase stand resilience to drought. However, information on tree and stand responses to thinning in older mixedwood stands is lacking. To address this need, a study was initiated in 2008 in Alberta, Canada in 14 boreal mixedwood stands (seven each at ages 17 and 22). This study investigated growth responses following thinning of aspen to five densities (0, 1000, 2500, 5000 stems ha−1 and unthinned (control)). Measurements were collected in the year of establishment, and three and eight years later. Mortality of aspen in the unthinned plots was greater than in the thinned plots which were not significantly different amongst each other. Eight years following treatment, aspen diameter was positively influenced by thinning, while there was no effect on aspen height. The density of aspen had no significant effect on the survival of planted spruce. Spruce height and diameter growth increased with both aspen thinning intensity and time since treatment. Differentiation among treatments in spruce diameter growth was evident three years from treatment, while differentiation in height was not significant until eight years following treatment. Yield projections using two growth models (Mixedwood Growth Model (MGM) and Growth and Yield Projection System (GYPSY)) were initialized using data from the year eight re-measurements. Results indicate that heavy precommercial aspen thinning (to ~1000 aspen crop trees ha−1) can result in an increase in conifer merchantable volume without reducing aspen volume at the time of harvest. However, light to moderate thinning (to ~2500 aspen stems ha−1 or higher), is unlikely to result in gains in either deciduous or conifer merchantable harvest volume over those of unthinned stands. [ABSTRACT FROM AUTHOR]

This paper presents a scaling approach for estimating sapwood area at the stand level using knowledge obtained for individual trees of five boreal species: Populus tremuloides (Michx.), Pinus contorta (Doug. ex Loud. var. latifolia Engelm.), Pinus banksiana (Lamb.), Picea mariana (Mill.) BSP, and Picea glauca (Moench) Voss. Previously developed allometric models for sapwood depth and diameter at breast height for individual tree species were used to build stand level sapwood area estimates as well as stand level leaf area estimates, in pure and mixed vascular vegetation stands. A stand's vegetation heterogeneity is considered in the scaling approach by proposing regression models for each species. The new combined scaling approach drew strong linear correlations at the stand scale between sapwood area and leaf area using observations taken in mixed stands of Southern Alberta, Canada. This last outcome suggests a good linear relationship between stand sapwood area and stand leaf area. The accuracy of the results was tested by observing each regression model's adequacy and by estimating the error propagated through the whole scaling process. [ABSTRACT FROM AUTHOR]