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A significant portion of the harvested land base in western Canada is becoming old enough or entering a phase where thinning is a legitimate forest management option. A comprehensive review of the existing knowledge of commercial thinning (CT) treatments applied to pine and spruce-dominated stands in Alberta was conducted, with particular regard to the intensity, timing of interventions, method, and impacts on crop tree growth responses. Although the geographical focus of this review is Alberta, information on this topic is more complete in other areas of North America and Europe, where there is a long history of density management. In areas of eastern North America, our review revealed that CT from below, with tree removal levels from 27 to 43% of the basal area, could increase total merchantable wood produced from 11 to 60 m3 ha−1 over a rotation, depending on stand age and intensity of thinning. For Alberta conditions, and considering the risks, we conclude that commercial thinning basal area removal should be in the range of 25 to 40%, depending on a variety of factors such as species, wind firmness, and insect or disease incidence and risk. Thinning too aggressively and/or too late will increase the blowdown risk but the literature is fairly consistent in suggesting that live crown ratios should be >40% to maximize the chance of growth response and minimize the blowdown risk. In cases where stands are also threatened by stressors such as drought, wind, and insect or disease outbreaks, CT treatments likely offer the potential at limiting the overall risk, but localized knowledge and experience are critical. It is intended that the information presented may support ongoing and future research trials and growth and yield (G&Y) model development about potential CT treatments to apply and the likely results of practical application to commercial forestry. [ABSTRACT FROM AUTHOR]

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While deployment of white spruce (Picea glauca (Moench) Voss) from seed orchards is increasing in Alberta, genetic gain is only considered in pure spruce stands due to uncertainties in measuring yields in mixedwood stands. To better understand the performance of improved spruce in mixedwood stands, we compared the effects of interspecific competition on growth of improved (1.9% height gain at a 100-year rotation) and unimproved spruce in northeastern Alberta. By age 8 years the improved spruce showed no advantage over the unimproved spruce in either height (1.36 ± 0.36 m vs. 1.42 ± 0.38 m) or diameter (23.68 ± 7.33 mm vs. 25.65 ± 6.85 mm), and the largest diameter trees were found in a nutrient-poor subxeric site. A distance-independent Lorimer's index including tree size ratio, combined with a power function, accounted for most of the growth variation in diameter and height from 2016 to 2017. The unimproved and improved spruce had different growth-competition curves across ecosites, and their height growth was less sensitive to competition than diameter growth. These results highlight several considerations for managing improved spruce, including (i) deploying higher genetic worth seedlots, (ii) developing realized gain trials with a good statistical design, and (iii) developing growth and yield functions for improved spruce in mixedwood stands. [ABSTRACT FROM AUTHOR]

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]

Climate change may have spatially variable impacts on growth of trees in topographically diverse environments, making generalizing across broad spatial and temporal extents inappropriate. Therefore, topography must be considered when analyzing growth response to climate. We address these topo-climatic relationships in the Canadian Rocky Mountains, focusing on lodgepole pine (Pinus contorta Douglas ex Louden) and interior spruce (Picea glauca (Moench) Voss × Picea engelmannii hybrid Parry) growth response to climate, Palmer drought severity index (PDSI), aspect, and slope angle. Climate variables correlate with older lodgepole pine growth on south- and west-facing slopes, including previous August temperature, winter and spring precipitation, and previous late-summer and current spring PDSI, but younger lodgepole pine were generally less sensitive to climate. Climate variables correlate with interior spruce growth on all slope aspects, with winter temperature and PDSI important for young and old individuals. Numerous monthly growth–climate correlations are not temporally stable, with shifts over the past century, and response differs by slope aspect and angle. Both species are likely to be negatively affected by moisture stress in the future in some, but not all, topographic environments. Results suggest species-specific and site-specific spatiotemporally diverse climate–growth responses, indicating that climate change is likely to have spatially variable impacts on radial growth response in mountainous environments. [ABSTRACT FROM AUTHOR]

Fundamental to the success of forest restoration following major disturbances such as mining is development of a functioning soil, including the amount, properties and rates of accumulation of soil organic matter (SOM). SOM enters mineral soil through leaching of dissolved organic matter from the forest floor; macrofaunal processing of above-ground litter and mixing with soil (bioturbation); and direct deposition of root litter and rhizodeposits. Our study focused on how SOM accumulation in reclaimed mineral soils was affected following re-vegetation with three vegetation treatments: deciduous trees (Populus tremuloides Mitchx. and Populus balsamifera L.), spruce trees (Picea glauca (Moench) Voss.) and grasses (Festuca sp., Bromus inermis), compared to the natural boreal forest. Seventeen sites were studied: 4 reclaimed Deciduous, 5 reclaimed Spruce, 4 reclaimed Grass, and 4 Natural forest. Concentrations of soil organic matter in the upper 30 cm of soil were highest at the Deciduous sites and lowest at Natural sites. SOM concentrations in the top 10 cm of soil were elevated relative to 10–30 cm soil at the Deciduous and Grass sites. The elevated SOM in the upper soil at Deciduous and Grass sites was associated with greater macrofauanal activity and higher root biomass at these sites. The higher macrofaunal activity in the surface organic layer and greater amounts of faunal fecal material in the uppermost cm of soil at Deciduous and Grass sites indicate greater enrichment of upper soil by macrofauna at these sites. SOM concentrations were significantly positively related to root abundance at Grass sites (indicating a contribution of roots to SOM), and a similar trend was apparent at the Deciduous sites. The elevated organic matter concentrations in the upper 10 cm of soil at the Deciduous and Grass sites suggest that planting of aspen following reclamation would hasten C sequestration into soil organic matter. [ABSTRACT FROM AUTHOR]

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]

• Tree species determine the soil fungal composition, especially in the root fraction. • Tree effects dominated, even when accounting for chemistry and spatial distribution. • In soil DNA, spruce samples contained more ectomycorrhizal and pine samples more saprotrophic taxa. • Siberian larch soils were associated with a greater abundance of pathogenic taxa. • Sporocarp surveys found more ectomycorrhizal and saprotrophic taxa in pine stands. Gateway Hill is a 104-ha area in the oil sands region of Alberta, which was operationally reclaimed and reforested in the late 1980s and certified as reclaimed in 2007/08. In 2014, ∼30 years after reclamation was completed, we began studies with the main objective to determine the soil fungi present at the site. Sporocarp surveys in 2014 and 2016 were used to supplement metagenomic analyses of soil fungi in jack pine (Pinus banksiana), white spruce (Picea glauca), and Siberian larch (Larix sibirica) stands. Fungal internal transcribed spacer amplicons of DNA extracted from forest floor, root, and fine soil fractions were sequenced using Roche 454 pyrosequencing in 2014. Coarse soil reclamation samples and soil samples from a nearby unmined spruce stand were sequenced with Illumina in 2016. Sequenced community assemblages were first assessed using unconstrained multivariate analyses, and then using (partially) constrained ordination techniques to directly account for the effects of tree species and other confounding factors. Based on soil DNA analyses the relative abundance of ectomycorrhizal taxa was greater in spruce stands, saprotrophs were more abundant in pine stands, and pathogens were more abundant in larch stands. Associations of fungal taxa, mostly saprotrophs and ectomycorrhizae, with tree species were especially prominent in root fractions. The sporocarp survey found sporcarp abundance was greatest in pine stands and they tended to have more ectomycorrhizal taxa and spruce and larch stands more saprotrophic taxa. The effects of tree species on fungal taxa differed between the sporocarp surveys and soil DNA analyses: many of the fungi identified by sporocarp presence were not detected by soil DNA sequencing, whereas the latter method detected many more species in all trophic groups. Both DNA sequencing methods showed that many operational taxonomic units were preferentially associated with either spruce or pine stands. Though not definitive, preliminary examination of soil fungi using the Illumina platform showed that a natural spruce stand at the base of Gateway Hill had greater species richness than did reclaimed spruce stands. The results of this study show that communities of soil fungi have become established since the initiation of reclamation. Further work is underway to compare this reclamation site to other unmined forest sites. [ABSTRACT FROM AUTHOR]