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Although the mining industry provides minerals and metals to the global market and represents important economic opportunities, it also constitutes a major anthropogenic disturbance in the ecosystems where it takes place. However,...
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Although the mining industry provides minerals and metals to the global market and represents important economic opportunities, it also constitutes a major anthropogenic disturbance in the ecosystems where it takes place. However, little is known about its offsite impacts on plant communities. We assessed the frequency and the abundance of five common boreal understorey plant species (Coptis trifolia (L.) Salisb., Cornus canadensis L., Linnaea borealis L., Lysimachia borealis (Raf.) U.Manns & Anderb., and Maianthemum canadense Desf.) at different distances around six mines in Abitibi-Temiscamingue and Nord-du-Quebec (Quebec). Frequency and (or) abundance of Coptis trifolia and M. canadense decreased near mines, suggesting that they might be sensitive to the loss of forest cover, particle deposition, and soil contamination induced by mining. Conversely, the frequency and abundance of Cornus canadensis increased near active mines, which indicates its resilience to the stress caused by mines and its ability to exploit the niche space left by more sensitive species. No effects on Linnaea borealis and Lysimachia borealis were observed. Our study suggests the possible presence of offsite impacts of mines on plant communities. Further studies considering enigmatic impacts should be conducted in order to develop our understanding of the broader environmental footprint of mining activity.
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Natural root grafting has been observed in more than 150 tree species where up to 90 % of trees could be interconnected within a stand. Intraspecific root grafting was previously found in Pinus banksiana stands, ranging from 21 to...
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Natural root grafting has been observed in more than 150 tree species where up to 90 % of trees could be interconnected within a stand. Intraspecific root grafting was previously found in Pinus banksiana stands, ranging from 21 to 71 % of trees grafted with one another. It is not known why root grafting is frequent in some species and not in others, or why not all roots that cross form root grafts. We investigated genetic diversity of grafted and non-grafted trees to determine if there was a relationship between genetic distance and the probability of forming natural root grafts. Seven plots were hydraulically excavated in four natural forest stands and three plantations of P. banksiana in the western boreal forest of Quebec, Canada. At pairs scale, we studied the effect of geographic and genetic distances on root grafting occurrence. At stand level, we analysed the effect of tree density, soil type, stand type and mean pairwise relatedness on the mean number of grafts per tree and on the percentage of grafted trees per plot. At pairs scale, our analysis revealed that root grafting presence was influenced by spatial distance between trees and less importantly, by genetic distance between individuals. At stand level, root grafting frequency was correlated with stand type (greater in naturally regenerated stands), but not with genetic diversity between individuals. In conclusion, root grafting appears to be principally linked to tree proximity and slightly to genetic proximity between individuals.
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Pruning one third of crown length in summer produced the least number of epicormic branches after two growing seasons. Epicormic branches can be removed without compromising tree growth.
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The variability in wood properties of eastern white cedar (Thuja occidentalis L.) is relatively poorly known. Here we report the axial and the radial variation in selected anatomical properties, namely, ring width, wood density, a...
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The variability in wood properties of eastern white cedar (Thuja occidentalis L.) is relatively poorly known. Here we report the axial and the radial variation in selected anatomical properties, namely, ring width, wood density, and tracheid length and width. Forty-five trees were randomly sampled and felled from three selected sites in the Abitibi-Temiscamingue region, Quebec, Canada. Disks were systematically sampled at 0.5, 1.3, and 3 m stem height and at every 2 meters thereafter up to the tree top. Average ring density at breast height was 355 kg/m(3) with a small difference between earlywood and latewood. The latewood proportion was uniform and constant within the tree at about 32%. The tracheids were fine and long, averaging 25.3 mu m in width and 2.07 mm in length. The variation in wood density components between trees was highly significant. The cambial age effect on all measured properties was highly significant. Ring density decreased from a maximum near the pith to a minimum in the juvenile-mature wood transition zone and remained constant or decreased slightly thereafter. Annual ring width decreased from a maximum near the pith to a minimum at the 10th ring and increased thereafter. Tracheid length and width showed typical radial variation characterized by a steady increase from pith to bark. Within-tree axial variation was highly significant, but ring width showed more substantial changes. Changes in wood properties with height depend on cambial age and thus are implied since the proportion of juvenile wood in the stem increases from the base to the top.
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This study compared growth of hybrid poplar in relation to soil mounding and mechanical weed control on a former agricultural site under boreal climate in order to assess optimal management scenarios. Height and basal diameter gro...
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This study compared growth of hybrid poplar in relation to soil mounding and mechanical weed control on a former agricultural site under boreal climate in order to assess optimal management scenarios. Height and basal diameter growth of 2 clones (Populus maximowiczii x P. balsamifera [915319] and P. x euramericana x P. maximowiczii [916401]) were evaluated after 3 growing seasons in 2 mounding (mounded, unmounded) and 4 weed control treatments (0: no weed control; 1, 2, and 3: 1, 2, or 3 passes of mechanical weed control). Net photosynthesis, stomatal conductance, soil temperature, and percent cover and height of competing vegetation were measured to explain the effects of soil mounding and weed control on tree growth. Two passes of weed control increased growth of trees by 23% in basal diameter and 12% in height, while mounding had no effect on growth. Both mounding and weed control reduced the cover of weedy vegetation, which was negatively correlated with growth of clone 915 319. Mounding did not increase mean soil temperatures in spring and even reduced them in the fall, while weed control had no effect on soil temperature. Finally, mounding significantly reduced the frequency and severity of damage (girdling) caused by voles during 2005-2006, especially for the plots that were not weeded.
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In the boreal forest, ground-layer composition may modulate the effects of precommercial thinning (PCT) on stand productivity by affecting tree growth conditions. Based on data from 15 years of PCT monitoring in black spruce (Pice...
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In the boreal forest, ground-layer composition may modulate the effects of precommercial thinning (PCT) on stand productivity by affecting tree growth conditions. Based on data from 15 years of PCT monitoring in black spruce (Picea mariana) and jack pine (Pinus banksiana) stands, the objectives of this study were to investigate the effects of PCT on ground-layer composition and the way ground-layer composition is related to tree growth, stand productivity, and the PCT impact on stand productivity. PCT favored lichen expansion in xeric sites. The positive impact of PCT on stand productivity after 15 years was lower in sites with high year-one lichen cover, suggesting that the aboveground positive effect of PCT on growth may have been mitigated by a belowground negative feedback resulting from lichen expansion in xeric sites. Although Sphagnum spp. cover was not affected by PCT, 15-year increase in stand productivity was lower in sites with high year-one Sphagnum spp. cover. These results suggest that xeric stands with high lichen cover should not be targeted for PCT because of either null or negative effects on stand productivity. Subhydric stands with high Sphagnum spp. cover should also be avoided because of lower potential stand productivity.
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Aim The main objective of this study was to evaluate the influence of leachates from three typical boreal forest ground layers on young tree growth and to explore the linkages between the chemical composition of the leachates, tre...
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Aim The main objective of this study was to evaluate the influence of leachates from three typical boreal forest ground layers on young tree growth and to explore the linkages between the chemical composition of the leachates, tree growth, the allocation between belowground and aboveground parts, and ectomycorrhizal colonization. Methods An original 6-month greenhouse experiment was set up to investigate (i) the effects of lichen (Cladoniaspp.) and feather moss (Pleurozium schreberii[Brid.] Mitt.) leachates on jack pine (Pinus banksianaLamb.) growth and (ii) the effects of feather moss andSphagnumspp. leachates on black spruce (Picea mariana[Mill.] B.S.P.) growth. Results Belowground growth and root allocation was reduced by lichen leachates in 2-year-old pine seedlings, while the impact was significant on both below- and aboveground growth in 6-month-old pine seedlings. A substance having the same migration time as usnic acid was detected in the lichen leachates by high-performance liquid chromatography.Sphagnumspp. and feather moss leachates were not found to have any effect on black spruce seedling growth, despite a higher supply of dissolved inorganic N in the feather moss leachates compared to the leachates ofSphagnumspp. and the control. Conclusions These results demonstrate that ground layer composition plays a crucial role in shaping the plant community in boreal ecosystems by influencing the chemical composition of the soil solution. They suggest that chemical interference may be another mechanism by which lichens promote the self-perpetuation of open woodlands in the closed-crown boreal forest.
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Relic old-growth forests are unique witnesses of long-term forest dynamics that can be used as reference conditions for ecosystem-based forest management. In temperate deciduous forests, catastrophic stand-replacing disturbances a...
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Relic old-growth forests are unique witnesses of long-term forest dynamics that can be used as reference conditions for ecosystem-based forest management. In temperate deciduous forests, catastrophic stand-replacing disturbances are rare, and stand dynamics are controlled by endogenous tree-by-tree replacement. Processes might be different at the northern distribution limit of temperate deciduous forests, because of differences in climate and disturbance regimes. We studied tree species composition, diameter, age, and spatial structures of 11 old-growth temperate deciduous stands across an age gradient. Stand characteristics differed from expectation, based on previous studies that were conducted in the central region of the range of temperate deciduous forests. Instead of increasing with age, tree species richness was higher in stands <120 years old because of the presence of relatively short-lived species such as Ables balsamea and Acer rubrum. All diameter distributions followed a two- or three-parameter Weibull model, instead of a rotated sigmoid. Some age structures showed recruitment pulses, contrary to the expectation of constant recruitment, and the spatial distribution of living trees was mostly random with regard to age and species at assessed distances (<14 m). In the context of ecosystem-based forest management, our results suggest that harvest levels should vary across harvesting blocks and selection silviculture should occasionally include larger, multiple-tree gaps in addition to single-tree gaps.
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Relic old-growth forests are unique witnesses of long-term forest dynamics that can be used as reference conditions for ecosystem-based forest management. In temperate deciduous forests, catastrophic stand-replacing disturbances a...
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Relic old-growth forests are unique witnesses of long-term forest dynamics that can be used as reference conditions for ecosystem-based forest management. In temperate deciduous forests, catastrophic stand-replacing disturbances are rare, and stand dynamics are controlled by endogenous tree-by-tree replacement. Processes might be different at the northern distribution limit of temperate deciduous forests, because of differences in climate and disturbance regimes. We studied tree species composition, diameter, age, and spatial structures of 11 old-growth temperate deciduous stands across an age gradient. Stand characteristics differed from expectation, based on previous studies that were conducted in the central region of the range of temperate deciduous forests. Instead of increasing with age, tree species richness was higher in stands <120 years old because of the presence of relatively short-lived species such as Ables balsamea and Acer rubrum. All diameter distributions followed a two- or three-parameter Weibull model, instead of a rotated sigmoid. Some age structures showed recruitment pulses, contrary to the expectation of constant recruitment, and the spatial distribution of living trees was mostly random with regard to age and species at assessed distances (<14 m). In the context of ecosystem-based forest management, our results suggest that harvest levels should vary across harvesting blocks and selection silviculture should occasionally include larger, multiple-tree gaps in addition to single-tree gaps.
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