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Yves Bergeron - One of the best experts on this subject based on the ideXlab platform.
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the predominance of Stand Composition and structure over direct climatic and site effects in explaining aspen populus tremuloides michaux site index within boreal and temperate forests of western quebec canada
2013Co-Authors: Kenneth A Anyomi, Yves Bergeron, Frederic Raulier, Daniel MaillyAbstract:Abstract Existing models that use the site-index concept (dominant canopy height of a tree species at a reference Stand age) are fundamentally Stand-level models that do not account for Stand dynamics, limiting their use to only a part of successional trajectories. Given that Stand dynamics is influenced by both large and fine scale processes, we took a multi-level look at aspen (Populus tremuloides Michaux) productivity by determining landscape- and plot-level factors related to productivity as rated with site index. The study area extends from latitude 45° to 50°N in western Quebec, from which were sampled 62 landscapes made up of 4948 plots, 25% of which had aspen as dominant and/co-dominants in the canopy. There, aspen is most often found in mixed Stands. A stepwise procedure with forward selection was used in building landscape- and plot-level models and models were then arranged hierarchically such that (a) predicted estimates of the landscape model were inputs to the plot-level model (top-down) and (b) significant landscape variables were added to selected plot level variables (bottom-up). For the plot-level model, none of the climate variables considered were selected but at the landscape level, annual sum of degree–days was only the third to enter. In both cases, aspen site index was more related to the proportion of spruce (Picea mariana (Mill.) B.S.P. and Picea glauca (Moench.) Voss). At the level of landscapes, this observation might be due to the existence of particular vegetation mosaics, of which spruce proportion could be a surrogate. At the level of plots, influence of spruce on aspen site index is probably indicative of niche sharing with aspen. A high random variability was associated with the plot-level model but not with the landscape-level model. The similarity in drivers of aspen site index at both levels and the fact that both top-down and bottom-up approaches provided the same information, suggest that the use of landscape variables when modelling site index in mixed Stands may help distinguish peculiarities shared by plots located in a landscape and improve the signal between site index and explanatory variables by reducing the random noise observed at the level of plots.
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forest dynamics after successive spruce budworm outbreaks in mixedwood forests
2006Co-Authors: Mathieu Bouchard, Yves Bergeron, Daniel KneeshawAbstract:In order to assess the long-term spatiotemporal influence of the spruce budworm in sub-boreal mixedwood forests, we studied the effect of three successive outbreaks in a region of western Quebec, Canada. We used dendrochronology to detect past outbreaks in three areas (111-185 ha), based on the recruitment age of balsam fir (Abies balsamea) and on growth patterns of white spruce (Picea glauca), the two main host species of this defoliating insect. We also used a series of aerial photographs taken between 1935 and 2003 to evaluate overstory mortality and post-outbreak succession patterns in these same areas. Individual outbreaks had a spatially homogenous impact on host species throughout the region, but successive outbreaks differed in intensity: the two outbreaks around 1910 and 1980 caused widespread mortality in the overstory, but an outbreak around 1945 had little impact, probably because the forest mosaic had not yet recuperated from the 1910 outbreak. No clear outbreak was detected in the later part of the 19th century. In portions of the study areas where the 1910 outbreak had a major impact, between 36% and 50% of the Stands were reoccupied by balsam fir Stands in the period up to the 1980 outbreak (cyclic succession), the rest being at least partly replaced by nonhost species such as Betula spp. Changes in forest Composition after the 1910 outbreak were mostly associated with upper-slope positions in all study areas. The 1980 outbreak also had a higher impact than earlier outbreaks in lower-slope positions dominated by black spruce (Picea mariana)-balsam fir mixtures. These results suggest that, at the regional scale, the abundance of mature or over-mature balsam fir Stands does not determine the outbreak cycle. When an outbreak occurs, however, its impact will be strongly constrained by forest characteristics such as Stand Composition and structure, which are themselves influenced by previous disturbances and slope position.
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effects of Stand Composition on fire hazard in mixed wood canadian boreal forest
2000Co-Authors: Christelle Hely, Yves BergeronAbstract:Surface fuels were examined in 48 Stands of the Canadian mixed-wood boreal forest. Tree canopy was charac- terized with the point-centred quadrant method and Stands were characterized as deciduous, mixed-deciduous, mixed- coniferous or coniferous according to the percentage of coni- fer basal area. Woody debris loadings were measured with the line intersect method and the litter, duff, shrub loads and depths or heights were sampled with various quadrats. No significant difference was found among Stand types for total woody debris load, large basal diameter shrub loads and load or depth of litter and duff. However, conifer Stands had signifi- cantly heavier loads of small diameter elements (twigs and shrubs) and conifer pieces were more numerous within these Stands than in deciduous Stands. The BEHAVE prediction system was used to evaluate the impact of these differences on the potential of fire ignition in situations where topography and weather were constant. The qualitative and quantitative changes in fuels, resulting from species replacement and fast decay rates, influence fire hazard. Simulations of fire behav- iour showed that in the mixed-wood boreal forest fires were less intense and spread more slowly in deciduous Stands than in mixed or coniferous Stands. Moreover, spring fires were more intense than summer fires, and differences between seasons increased with the increase of deciduous basal area.
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relationships between change in fire frequency and mortality due to spruce budworm outbreak in the southeastern canadian boreal forest
1998Co-Authors: Yves Bergeron, Alain LeducAbstract:. We present a simple empirical model that allows an estimation of mortality due to spruce budworm (Choristoneura fumiferana) outbreak in relation to fire frequency and site characteristics. The occurrence of a recent spruce budworm outbreak around Lake Duparquet (48° 30’N, 79° 20’W, ca. 300 m a.s.l.) in northwestern Quebec permitted a reconstruction of the Stand Composition before the outbreak, and also of the mortality of Abies balsamea due to the outbreak. The basal area of A. balsamea increases with time since fire in all site types but with increasing values for (1) rock and shallow till, via (2) till and mesic clay up to (3) hydric clay. Mortality (measured as percentage loss of basal area due to the outbreak) increases with time since fire but did not vary with site type. The increasing abundance of A. balsamea with time since fire is mainly responsible for this increase in mortality. Mortality for a specific basal area is, however, lower for the more recently burned Stands suggesting a significant residual effect of time since fire. A landscape model integrating mortality due to the outbreak for Stands of different age is developed. Both absolute and relative losses of basal area increased with the length of the fire cycles. According to this model, changes in fire cycle could explain a large portion of the spatio-temporal variations observed in outbreak mortality in the southeastern boreal forest of Canada.
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changes in nutrient availability and forest floor characteristics in relation to Stand age and forest Composition in the southern part of the boreal forest of northwestern quebec
1995Co-Authors: Yves Bergeron, Suzanne Brais, Claude Camire, David PareAbstract:Abstract Changes in forest floor properties and nutrient availability along a boreal post-fire sere succession covering a time span of 231 years were assessed using soil analysis and exchange resins. A decline in pH (from 5.5 to 3.65), effective cation exchange capacity (CEC) (from 72.5 to 39.6 cmol(+)kg−1), exchangeable cation concentrations, as well as in Ca, Mg, K and PO4 concentrations on resin was observed. Contrary to what has been reported so far for boreal forests, NO3 and NH4 concentrations did not decrease in the course of succession. Ammonium concentrations remained constant while those of NO3 reached their highest values at age 27, decreased abruptly between ages 27 and 47, and started to increase in older Stands. No correlation was found between NO3 availability and pH, P concentrations or C/N ratio. Interactive effects of Stand age and Stand Composition on nutrient concentrations on resins were evaluated using path analysis. While it is not possible to fully disentangle the contribution of single factors, the results showed a positive effect of aspen on Ca concentrations. These results stressed the need to evaluate the long term impacts of successive rotations of softwood species coupled with the elimination of hardwood competition on the soil base status of plantations.
Juan C Corley - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Spatial Pattern of Attacks of the Invasive Woodwasp Sirex noctilio, at Landscape and Stand
2016Co-Authors: Victoria M Lantschner, Juan C CorleyAbstract:Invasive insect pests are responsible for important damage to native and plantation forests, when population outbreaks occur. UnderStanding the spatial pattern of attacks by forest pest populations is essential to improve our underStanding of insect population dynamics and for predicting attack risk by invasives or planning pest management strategies. The woodwasp Sirex noctilio is an invasive woodwasp that has become probably the most im-portant pest of pine plantations in the Southern Hemisphere. Our aim was to study the spa-tial dynamics of S. noctilio populations in Southern Argentina. Specifically we describe: (1) the spatial patterns of S. noctilio outbreaks and their relation with environmental factors at a landscape scale; and (2) characterize the spatial pattern of attacked trees at the Stand scale. We surveyed the spatial distribution of S. noctilio outbreaks in three pine plantation landscapes, and we assessed potential associations with topographic variables, habitat characteristics, and distance to other outbreaks. We also looked at the spatial distribution of attacked trees in 20 Stands with different levels of infestation, and assessed the relationship of attacks with Stand Composition and management. We found that the spatial pattern of pine Stands with S. noctilio outbreaks at the landscape scale is influenced mainly by the host species present, slope aspect, and distance to other outbreaks. At a Stand scale, there is strong aggregation of attacked trees in Stands with intermediate infestation levels, and the degree of attacks is influenced by host species and plantation management. We con-clude that the pattern of S. noctilio damage at different spatial scales is influenced by a com-bination of both inherent population dynamics and the underlying patterns of environmental factors. Our results have important implications for the underStanding and management of invasive insect outbreaks in forest systems
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spatial pattern of attacks of the invasive woodwasp sirex noctilio at landscape and Stand scales
2015Co-Authors: Victoria M Lantschner, Juan C CorleyAbstract:Invasive insect pests are responsible for important damage to native and plantation forests, when population outbreaks occur. UnderStanding the spatial pattern of attacks by forest pest populations is essential to improve our underStanding of insect population dynamics and for predicting attack risk by invasives or planning pest management strategies. The woodwasp Sirex noctilio is an invasive woodwasp that has become probably the most important pest of pine plantations in the Southern Hemisphere. Our aim was to study the spatial dynamics of S. noctilio populations in Southern Argentina. Specifically we describe: (1) the spatial patterns of S. noctilio outbreaks and their relation with environmental factors at a landscape scale; and (2) characterize the spatial pattern of attacked trees at the Stand scale. We surveyed the spatial distribution of S. noctilio outbreaks in three pine plantation landscapes, and we assessed potential associations with topographic variables, habitat characteristics, and distance to other outbreaks. We also looked at the spatial distribution of attacked trees in 20 Stands with different levels of infestation, and assessed the relationship of attacks with Stand Composition and management. We found that the spatial pattern of pine Stands with S. noctilio outbreaks at the landscape scale is influenced mainly by the host species present, slope aspect, and distance to other outbreaks. At a Stand scale, there is strong aggregation of attacked trees in Stands with intermediate infestation levels, and the degree of attacks is influenced by host species and plantation management. We conclude that the pattern of S. noctilio damage at different spatial scales is influenced by a combination of both inherent population dynamics and the underlying patterns of environmental factors. Our results have important implications for the underStanding and management of invasive insect outbreaks in forest systems.
Samuel B St Clair - One of the best experts on this subject based on the ideXlab platform.
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herbivory impacts of elk deer and cattle on aspen forest recruitment along gradients of Stand Composition topography and climate
2017Co-Authors: Aaron C Rhodes, Ho Yi Wan, Samuel B St ClairAbstract:Abstract The abundance and Composition of large ungulate communities are changing dramatically across terrestrial ecosystems due to human activities. This has resulted in novel herbivory regimes that create strong top-down effects on biological communities, and can reduce ecosystem resilience. Biotic and abiotic conditions that influence the population structure and behavior of ungulate herbivores are highly variable across space and time, making it difficult to predict ungulate impacts across complex landscapes. Where multiple ungulate species co-exist, it can be challenging to differentiate species impacts on plant communities. We examined the effects of cattle, American elk, and mule deer on aspen regeneration and recruitment along gradients of forest Composition and physiographic conditions in 3 National Forests of Utah, USA. Aspen regeneration and recruitment increased with winter precipitation, elevation and higher abundance of overstory aspen. Binned fecal count densities of elk, mule deer, and cattle showed strong inverse correlations with aspen height (elk: r 2 = 0.83; deer: r 2 = 0.92; cattle: r 2 = 0.35) and aspen recruitment (elk: r 2 = 0.51; deer: r 2 = 0.59). Aspen stem density was negatively correlated with elk (r 2 = 0.35) and cattle fecal densities (r 2 = 0.71). We found that 60% of the sites we surveyed had low ungulate activity and good aspen regeneration, 32% were intermediate use sites that warrant additional monitoring, and 8% of sites showed high ungulate use that exhibited aspen regeneration failure and lack of recruitment where targeted management is recommended. We conclude that ungulate impacts in aspen forests should be considered on a site by site basis and should primarily be evaluated based on the total abundance of the ungulate community with precipitation, elevation and Stand Composition as secondary factors.
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Stand Composition tree proximity and size have minimal effects on leaf function of coexisting aspen and subalpine fir
2016Co-Authors: Aaron C Rhodes, Trevor Barney, Samuel B St ClairAbstract:Forest structural heterogeneity due to species Composition, spatial relationships and tree size are widely studied patterns in forest systems, but their impacts on tree function are not as well documented. The objective of this study was to examine how Stand Composition, tree proximity relationships and tree size influence the leaf functional traits of aspen, an early successional species, and subalpine fir, a climax species. We measured foliar nutrients, nonstructural carbohydrates (aspen only), defense chemistry and xylem water potential of aspen and subalpine fir trees in three size classes growing in close proximity or independently from other trees under three Stand conditions: aspen dominant, aspen-conifer mixed, and conifer dominant Stands. Close proximity of subalpine fir to aspen reduced aspen’s storage of starch in foliar tissue by 17% suggesting that competition between these species may have small effects on carbon metabolism in aspen leaves. Simple sugar (glucose + sucrose) concentrations in aspen leaves were slightly higher in larger aspen trees than smaller trees. However, no differences were found in stem water potential, foliar concentrations of nitrogen, phosphorus, or secondary defense chemicals of aspen or subalpine fir across the gradients of Stand Composition, tree proximity or tree size. These results suggest that mechanisms of coexistence allow both aspen and subalpine fir to maintain leaf function across a wide range of Stand structural characteristics. For aspen, resource sharing through its clonal root system and high resource storage capacity may partially contribute to its functional stability in mixed aspen-conifer Stands.
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Stand Composition proximity to overstory trees and gradients of soil moisture influence patterns of subalpine fir seedling emergence and survival
2014Co-Authors: Joshua R Buck, Samuel B St ClairAbstract:Background and Aims We experimentally examined how variability in mixed forest Stand Composition, spatial relationships to dominant trees and their environmental correlates influence seedling emergence and survival.
Victoria M Lantschner - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Spatial Pattern of Attacks of the Invasive Woodwasp Sirex noctilio, at Landscape and Stand
2016Co-Authors: Victoria M Lantschner, Juan C CorleyAbstract:Invasive insect pests are responsible for important damage to native and plantation forests, when population outbreaks occur. UnderStanding the spatial pattern of attacks by forest pest populations is essential to improve our underStanding of insect population dynamics and for predicting attack risk by invasives or planning pest management strategies. The woodwasp Sirex noctilio is an invasive woodwasp that has become probably the most im-portant pest of pine plantations in the Southern Hemisphere. Our aim was to study the spa-tial dynamics of S. noctilio populations in Southern Argentina. Specifically we describe: (1) the spatial patterns of S. noctilio outbreaks and their relation with environmental factors at a landscape scale; and (2) characterize the spatial pattern of attacked trees at the Stand scale. We surveyed the spatial distribution of S. noctilio outbreaks in three pine plantation landscapes, and we assessed potential associations with topographic variables, habitat characteristics, and distance to other outbreaks. We also looked at the spatial distribution of attacked trees in 20 Stands with different levels of infestation, and assessed the relationship of attacks with Stand Composition and management. We found that the spatial pattern of pine Stands with S. noctilio outbreaks at the landscape scale is influenced mainly by the host species present, slope aspect, and distance to other outbreaks. At a Stand scale, there is strong aggregation of attacked trees in Stands with intermediate infestation levels, and the degree of attacks is influenced by host species and plantation management. We con-clude that the pattern of S. noctilio damage at different spatial scales is influenced by a com-bination of both inherent population dynamics and the underlying patterns of environmental factors. Our results have important implications for the underStanding and management of invasive insect outbreaks in forest systems
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spatial pattern of attacks of the invasive woodwasp sirex noctilio at landscape and Stand scales
2015Co-Authors: Victoria M Lantschner, Juan C CorleyAbstract:Invasive insect pests are responsible for important damage to native and plantation forests, when population outbreaks occur. UnderStanding the spatial pattern of attacks by forest pest populations is essential to improve our underStanding of insect population dynamics and for predicting attack risk by invasives or planning pest management strategies. The woodwasp Sirex noctilio is an invasive woodwasp that has become probably the most important pest of pine plantations in the Southern Hemisphere. Our aim was to study the spatial dynamics of S. noctilio populations in Southern Argentina. Specifically we describe: (1) the spatial patterns of S. noctilio outbreaks and their relation with environmental factors at a landscape scale; and (2) characterize the spatial pattern of attacked trees at the Stand scale. We surveyed the spatial distribution of S. noctilio outbreaks in three pine plantation landscapes, and we assessed potential associations with topographic variables, habitat characteristics, and distance to other outbreaks. We also looked at the spatial distribution of attacked trees in 20 Stands with different levels of infestation, and assessed the relationship of attacks with Stand Composition and management. We found that the spatial pattern of pine Stands with S. noctilio outbreaks at the landscape scale is influenced mainly by the host species present, slope aspect, and distance to other outbreaks. At a Stand scale, there is strong aggregation of attacked trees in Stands with intermediate infestation levels, and the degree of attacks is influenced by host species and plantation management. We conclude that the pattern of S. noctilio damage at different spatial scales is influenced by a combination of both inherent population dynamics and the underlying patterns of environmental factors. Our results have important implications for the underStanding and management of invasive insect outbreaks in forest systems.
John R Spence - One of the best experts on this subject based on the ideXlab platform.
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influence of Stand Composition on predatory mite mesostigmata assemblages from the forest floor in western canadian boreal mixedwood forests
2013Co-Authors: Irma Diazaguilar, Sylvie A Quideau, Barbara E Kishchuk, Heather C Proctor, John R SpenceAbstract:Abstract Mesostigmatan mites dwelling in forest floors are the least abundant of soil mesofauna, however, they play an important role by regulating population sizes of other microarthropods. In this study, we evaluate the impact of Stand type on the structure and community Composition of predator mites from the Mesostigmata order in forest floors from undisturbed deciduous Stands dominated by Populus tremuloides , coniferous Stands dominated by Picea glauca , and mixed Stands in the western Canadian boreal forest. We observed differences in species richness, dominance and community Composition among the Stand types. Coniferous and mixed Stands had higher mesostigmatan species richness than deciduous Stands. Coniferous Stands had a different community Composition than deciduous and mixed Stands, indicating the importance of coniferous trees in structuring mesostigmatan assemblages. Although forest floor pH varied within a narrow range, it was important in explaining variations in mesostigmatid community Composition. Mesostigmatan assemblages were also distinguished according to forest floor thickness, probably reflecting species-specific habitat preferences within accumulated litter. Maintaining coniferous trees will be necessary for conserving the natural patterns of mesostigmatan mites in western Canadian boreal mixedwood forests.
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seed tree density variable retention and Stand Composition influence recruitment of white spruce in boreal mixedwood forests
2010Co-Authors: John R Spence, Jan W A Volney, Kevin A Solarik, Victor J Lieffers, Rick Pelletierr PelletierAbstract:In an operational-scale experiment, we examined natural regeneration of white spruce (Picea glauca (Moench) Voss) under various degrees of variable retention harvesting across different overstory c...
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Stand Composition and structure of the boreal mixedwood and epigaeic arthropods of the ecosystem management emulating natural disturbance emend landbase in northwestern alberta
2004Co-Authors: Timothy T Work, David Shorthouse, John R Spence, Jan W A Volney, David W LangorAbstract:Conservation of biological diversity under the natural disturbance model of boreal forest management relies on the assumption that natural mosaics of Stand Composition and structure can be adequately recreated through forest management activities. Maintaining Compositional and structural features that provide adequate habitat for species within managed Stands is the basis of coarse-filter conservation strategies. Here we test the effect of Stand Composition and Stand structure on the epigaeic arthropod fauna from four boreal mixedwood cover types in western Canada. We observed differences in epigaeic community Composition and species-specific associations among each of the four cover types. Differences in the carabid fauna between cover types were defined by relative abundance of carabid species as- sociated specifically with moss cover, forb cover, and of coarse woody material, rather than unique, Stand-specific spe- cies Compositions of the overstory. Cover-type differences were less apparent among the comparatively species-rich spider assemblages largely because of their low abundance in undisturbed Stands. For the effective conservation of all species, our results suggest that coarse-filter management of mixedwood boreal forests must incorporate structural fea- tures beyond overstory canopy Composition. Our analyses also suggest that activities directed at managing the amount of coarse woody material on the ground and understory plant Composition, perhaps through variable retention harvest- ing, is a logical first step.
