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Natural disturbance‐based management (NDBM) is hypothesized to maintain managed forest ecosystem integrity by reducing differences between natural and managed forests. The effectiveness of this approach often entails local comparisons of species composition or diversity for a variety of biota from managed and unmanaged forests. Understory vegetation is regularly the focus of such comparison because of its importance in nutrient cycling, forest regeneration, and for wildlife. However, larger scale comparisons between regions with distinct species assemblages may require a trait‐based approach to better understand understory responses to disturbance. We compared the long‐term effects of retention harvesting on understory vegetation in two large experimental study sites located in eastern and western regions of the Canadian boreal forest. These sites included the Sylviculture en Aménagement Forestier Ecosystémique (SAFE) experiment and the Ecosystem Management Emulating Natural Disturbance (EMEND) experiment, located in the eastern and western regions of Canada, respectively. EMEND and SAFE share common boreal understory species but have distinct tree communities, soils, and climate. Both experiments were designed to evaluate how increasing tree retention after harvest affects biodiversity. Here, we examined taxonomic richness, functional diversity, and functional composition (using community trait mean values) of understory plant communities, and also examine intraspecific trait variability (ITV) for five species common and abundant in both experiments. We observed the limited impacts of retention level on richness, functional diversity, and functional composition of understory plants 20 years postharvest. However, ITV of leaf morphological traits varied between retention levels within each experiment, depending on the species identity. Common species had different functional responses to retention level, showing species‐specific reactions to environmental variation. Our result suggests that understory plant communities in the boreal forest achieve resilience to disturbance both in terms of interspecific and intraspecific functional trait diversity. Such diversity may be key to maintaining understory biodiversity in the face of future disturbances and environmental change. Our results reveal the significance of ITV in plant communities for understanding responses to forest harvesting and the importance of choosing appropriate traits when studying species responses to the environment. [ABSTRACT FROM AUTHOR]

The most rapid climate warming is occurring in northern, permafrost environments. Peatlands of these regions are particularly sensitive to climate warming, with the high ground ice content of peat plateaux resulting in the formation of collapse scars as ground temperatures warm.To quantify the rates of permafrost thaw and associated vegetation changes, we sampled the plant and lichen communities in transects spanning actively thawing collapse scar margins at sites from mid‐Boreal to Low Subarctic conditions, within Canada's Northwest Territories. Seventeen transects were sampled in 2007/08 and 14 of these were resampled 10 years later.The rate of lateral permafrost thaw of collapse scar margins ranged from −6 to 63 cm year−1 (mean: 22.0 cm ± 4.7 cm year−1 (SE)); variability was high and no trends with respect to latitude or temperature gradients were detected.Plant communities displayed a clear gradient from lichen‐ and ericaceous shrub‐dominated peat plateaux, to collapse scars primarily characterized by Sphagnum mosses and graminoids. Both space‐for‐time (distance from collapsing margin) and direct measurement of 10‐year changes showed a successional sequence following permafrost thaw; floating mat communities characterized by Sphagnum riparium or S. balticum proceeded to lawn communities of S. angustifolium and, finally, to hummock communities with Mylia anomala or S. fuscum. This successional sequence was associated with increased water table depth and lower soil water content in plant communities farther from the actively collapsing front, illustrating that peat growth above the water table was driving plant community successional changes.The most rapid plant community succession occurred in recently thawed environments as peat growth propelled the ground surface above the water table while the slowest succession occurred in the collapse scar hummock communities located farthest from the actively collapsing peat plateau margin.Synthesis. In just 10 years, significant vegetation change was detected, in association with both permafrost thaw and subsequent plant community succession. These changes occurred across a broad climatic and latitudinal gradient, from mid‐Boreal to Low Subarctic and have implications for wildlife, global C cycle and indigenous communities who depend on this landscape for harvesting, spiritual and cultural practices. [ABSTRACT FROM AUTHOR]

The recent expansion of mountain pine beetle (MPB, Dendroctonus ponderosae) from its native range in western North America into northern boreal pine forests in Alberta, Canada has resulted in conditions for tree regeneration that are dramatically different from those after wildfire, the predominant natural disturbance in these forests. We assessed natural regeneration post-MPB for northern boreal lodgepole pine sites in Alberta, Canada via intensive surveys of small plots at 33 severely attacked pine stands and using data from 205 permanent sample plots representing various site types and levels of MPB mortality. We used model selection to identify factors explaining regeneration. Overall, pine regeneration was very poor 6–9 years post-MPB; only 42% of the 33 intensively surveyed plots and only 9% of the 205 permanent plots had pine seedlings. This poor regeneration is attributed to high levels of cone serotiny in these populations, unsuitable regeneration microsites due to undisturbed litter or feathermoss layers, and competition from the residual canopy and understory vegetation. Other species (aspen, birch, poplar, and black and white spruce) were found on most sites, either as post-attack regeneration or regeneration established in advance. Without intervention, many of these stands will likely transition away from pine, to broadleaf and other conifer species. [ABSTRACT FROM AUTHOR]

Oil sands mining in northeastern Alberta, Canada, generates tailings containing sand, silt, clay, water, and residual bitumen with hydrocarbons. The impact of tailings on revegetation is a major environmental concern and poses a significant land reclamation challenge. Oil sands companies have recently developed technologies that use thickeners in combination with carbon dioxide to produce non‐segregating tailings (NST), to accelerate the consolidation of tailings while sequestering greenhouse gases. Effects of these tailings on plant re‐establishment have yet to be determined. We investigated the impact of NST on biomass and physiology of 20 boreal woody plant species grown in environmentally controlled growth rooms. The seedlings were grown for 8 weeks in NST capped with boreal forest topsoil or peat‐mineral soil mix or petroleum coke in 50‐cm‐long polyvinyl chloride pipes. We found that the biomass of balsam fir, beaked hazelnut, blueberry, green alder, Labrador tea, lowbush cranberry, paper birch, and raspberry was severely reduced by NST, while the effects on balsam poplar, Bebb's willow, chokecherry, dogwood, saskatoon, and white spruce were relatively weak. This was also the case for jack pine, which showed poor survival in NST. The negative impact of NST on plants can be largely explained by elevated sodium and decreased foliar nutrient concentrations. The impact of NST capping with petroleum coke on plant growth was non‐significant. Differences among species in their survival and biomass responses to NST appeared to be partly a reflection of their natural habitats. Findings from this study can help guide revegetation oil sands reclamation strategies. [ABSTRACT FROM AUTHOR]

Retention harvesting is advocated as an alternative to intensive timber harvesting, such as clear‐cutting, to better maintain or facilitate recovery of biodiversity and other ecological values in managed forests. However, it is not clear how long the benefits of retention harvests persist.We investigated responses of understory vascular plant cover, richness, diversity (inverse Simpson index) and composition to a gradient in dispersed retention (2% [clear‐ cut], 10%, 20%, 50% and 75% retention; unharvested reference [100% retention]) at 3, 6, 11, and 17 years after harvest, in four boreal mixedwood forest types (deciduous (broadleaf)‐dominated, deciduous‐dominated with conifer understory, mixed, and conifer‐dominated) in western Canada.Understory cover and richness tended to increase in the short‐term (3 years), peaked at 6–11 years with differences following the gradient of harvesting intensity, then plateaued or declined in the second decade (17 years), by which time there were minimal or no differences among harvesting levels, including the reference. Responses for diversity were minimal. In contrast, composition varied along the gradient of harvesting intensity and showed little recovery towards the unharvested condition over the 17‐year period. Generally, for plant community composition, clear‐cut and lower retention treatments (10%, 20%) were similar to one another but differed from the higher retention and unharvested reference treatments.Synthesis and applications: Retention harvests can moderate the negative impacts of harvesting and facilitate the recovery of biodiversity. Our results suggest that for the cover, richness and diversity of understory vascular plants, this moderating influence is weak and short‐lived. However, higher levels of retention can temper changes in understory composition relative to the unharvested forest, but full recovery is likely to be slow and will be complicated by post‐harvest regeneration dynamics. [ABSTRACT FROM AUTHOR]

Treed peatlands are dominated by bryophytes, particularly Sphagnum spp., which create the characteristic hummock‐hollow microtopography. This, in turn, shapes the distribution of bryophyte communities. Disturbances can lead to a loss of this microtopographic variation, impacting the bryophyte community. Seismic lines are deforested linear disturbances (approximately 3–8 m wide) created during oil and gas exploration and very extensive in Alberta, Canada. Loss of microtopographic variation leads to slow tree recovery on seismic lines in treed peatlands. To facilitate tree establishment, mounding is being applied to restore the microtopography on seismic lines. We compared bryophyte communities on unmounded and mounded seismic lines (18 years after seismic line creation, 3 years after mounding), and in adjacent treed fens as the reference, to evaluate how recovery varies with microtopographic position (i.e., top of hummock, slope or side of the hummock, and level ground). We found that recovery on the unmounded seismic lines was underway 18 years after seismic lines were created, while mounding redisturbed the sites and thus set back recovery, at least in the short term (3 years post‐mounding). In unmounded seismic lines, Sphagnum cover was similar to that of reference treatments at all microtopographic positions. In contrast, mounded seismic lines had lower Sphagnum cover and higher cover of true mosses (sans feather mosses) than reference and unmounded treatments. Overall, these results show mounding sets back the recovery of bryophyte communities—the very organisms responsible for the microtopographic variation we are trying to establish. Further monitoring is needed to understand how this changes over time. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ecology is the property of Wiley-Blackwell 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.)

Climate warming in the North could lead to lichen decline within critical woodland caribou habitat. We used repeat measurements of sixty-nine plots over ten years (2007-2008 and 2017-2018) to assess lichen biomass changes under a warming climate along a latitudinal/climatic gradient in northwestern Canada. We compared lichen biomass on sensitive landscape features, including peat plateaux (permafrost-containing bogs), areas of permafrost thaw within the peat plateaux (collapse scars), and low-productivity upland forests occurring on mineral soils. Field-based measures of lichen cover and height were coupled with samples of lichen biomass to develop biomass prediction equations. The optimal model incorporated both cover and height, with landscape feature as a covariate. Although height significantly improved the equation fit, models were successfully developed with cover alone. Modeled lichen biomass differed significantly between landscape features, declining from peat plateau (502 g m-2) to upland forest (54.0 g m-2) and collapse scar (0.690 g m-2) environments. In the absence of permafrost collapse at any monitoring location, lichen biomass declined significantly over the ten years for peat plateaux (-75.6 g m-2) and upland forests (-17.5 g m-2). These results will be important for quantifying landscape-level lichen biomass changes under climate warming in boreal and subarctic environments. [ABSTRACT FROM AUTHOR]

Questions: Edge influence on forest biodiversity is an important environmental effect associated with habitat fragmentation, but extrapolating the influence of edges across the broader landscape has been difficult, especially for situations where multiple edges exist in close proximity. We asked whether there were differences in edge effects between two types (3 m vs 8 m width) of low‐severity linear disturbance (seismic lines) and whether there were interactions of edge effects when seismic lines occur in dense networks; that is, do multiple narrow seismic lines have a stronger or weaker edge influence than a single narrow seismic line. Location: Treed peatlands in northeastern Alberta, Canada. Methods: Seismic lines are created during oil and gas exploration and are responsible for dissection of boreal forests in western Canada. We sampled vascular plants along transects perpendicular to seismic lines in moderate‐rich and poor treed fens. We used the "Randomization Test of Edge Influence" (RTEI) to calculate the magnitude and distance of edge effects and then compared these between narrower (3 m) versus wider (8 m) lines and between single narrow lines versus multiple narrow lines (parallel and ~50 m apart). Results: In moderate‐rich fens, we found a positive edge influence on understorey diversity from both wide and narrow seismic lines. We also found a weakening edge interaction on diversity, that is, single narrow seismic lines had a stronger edge influence on diversity than did multiple narrow seismic lines. In treed poor fens, multiple narrow seismic lines had a negative edge effect on tree density, understorey abundance, richness, and composition. In addition, we found strengthening edge interactions in treed poor fens on tree density, graminoid cover, and understorey composition. Conclusions: Even narrow linear disturbances, such as seismic lines, can have significant edge effects and these are exacerbated when lines occur in dense networks. [ABSTRACT FROM AUTHOR]

Many studies have focused on vegetation across forest edges to study impacts of edges created by human activities on forest structure and composition, or patterns of vegetation at inherent natural edges. Our objective was to create a database of plant‐related variables across different types of edges from various studies (mainly from across Canada, but also in Brazil and Belize) to facilitate edge research. We compiled data on vegetation along more than 300 transects perpendicular to forest edges adjacent to clear‐cuts, burned areas, bogs, lakes, barrens, insect disturbances, and riparian areas from 24 studies conducted over the past three decades. Data were compiled for more than 400 plant species and forest structure variables (e.g., trees, logs, canopy cover). All data were collected with a similar sampling design of quadrats along transects perpendicular to forest edges, but with varying numbers of transects and quadrats, and distances from the edge. The purpose for most of the studies was either to determine the distance of edge influence (edge width) or to explore the pattern of vegetation along the edge to interior gradient. We provide data tables for the cover of plant species and functional groups, the species and size of live and dead trees, the density of saplings, maximum height of functional groups and shrub species, and the cover of functional groups at different heights (vertical distribution of vegetation). The Forest Edge Research Network (FERN) database provides extensive data on many variables that can be used for further study including meta‐analyses and can assist in answering questions important to conservation efforts (e.g., how is distance of edge influence from created edges affected by different factors?). We plan to expand this database with subsequent studies from the authors and we invite others to contribute to make this a more global database. The data are released under a CC0 license. When using these data, we ask that you cite this data paper and any relevant publications listed in our metadata file. We also encourage you to contact the first author if you are planning to use or contribute to this database. [ABSTRACT FROM AUTHOR]

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.)

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.)

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.)

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.)

Site moisture is an important component of the forest landscape for maintaining biodiversity, including forest‐floor bryophytes. However, little is known about its role in shaping understorey responses to harvesting.We investigated the influence of site wetness, determined using a remotely sensed, topographic depth‐to‐water (DTW) index, on responses of bryophyte cover, richness, diversity and composition to variable retention harvesting (comparing: 2% [clear‐cut], 20% and 50% dispersed green tree retention and uncut controls [100% retention]) in three boreal forest cover‐types (broadleaf, mixed and conifer forests) in western Canada. The DTW index provides an approximation of DTW at or below the soil surface and was derived from wet‐areas mapping based on discrete Airborne Laser Scanning data acquired over an experimentally harvested landscape located in north‐western Alberta, Canada.The effectiveness of leaving retention (vs. clear‐cutting) for conserving bryophyte communities depended on site wetness, as indicated by DTW, with the specifics varying among forest types. In broadleaf forests, bryophyte cover and richness were generally low and not much affected by harvesting but drier sites had higher richness and a few more unique species. In mixed and conifer forests, leaving retention (vs. clear‐cutting) on wetter (vs. drier) sites was more effective for conserving bryophyte cover, wetter sites had higher total species richness and more species were exclusive to wetter sites.Synthesis and applications. Site wetness, as indicated using the remotely sensed topographic site wetness index "depth‐to‐water" mediates bryophyte responses to variable‐retention harvests. Specifically, our results suggested that in conifer and mixed forests it would be more beneficial to target wetter sites for retention patches or dispersed retention whereas in broadleaf forests there might be a slight advantage to targeting drier sites. Our study demonstrates that this tool could be used to inform management decisions around leaving dispersed or patch retention. Site wetness, as indicated using the remotely sensed topographic site wetness index "depth‐to‐water" mediates bryophyte responses to variable‐retention harvests. Specifically, our results suggested that in conifer and mixed forests it would be more beneficial to target wetter sites for retention patches or dispersed retention whereas in broadleaf forests there might be a slight advantage to targeting drier sites. Our study demonstrates that this tool could be used to inform management decisions around leaving dispersed or patch retention. [ABSTRACT FROM AUTHOR]

Abstract: Retention harvesting (also called tree retention or structural retention), in which live mature trees are selectively retained within harvested stands at different retention levels and in different patterns (aggregated to dispersed), is increasingly being used to mitigate the negative impacts of forest harvesting on biodiversity. However, the effectiveness of combining different patterns of retention harvesting for conservation and recovery of understory vascular plants in the long term is largely unknown. To address this gap, we compared understory vascular plant diversity, abundance, and composition between aggregated retention and five levels of surrounding dispersed retention (0% [clearcut], 10%, 20%, 50%, 75%) 15 yr postharvest. We also investigated the influence of dispersed retention on the ability of embedded retention patches to support plant communities characteristic of unharvested forests, and whether it varies by patch size of aggregated retention (0.20 ha or 0.46 ha) and position within patches (edge or interior). Species richness, diversity, and cover were higher in the dispersed retention than in the patch retention as the harvested areas favored early‐seral plant species. Graminoid cover was greater at the edges than in the interior of large patches. Retention patches as small as 0.2 ha more effectively supported shade‐tolerant (forest interior) plant communities when they were surrounded by higher levels of dispersed retention (as compared to patches retained within clearcuts). Overall, the combined use of both aggregated and dispersed retention within a given cutblock benefits both late‐ and early‐seral plant species and thus could effectively conserve understory plant assemblages in harvested landscapes. Sustainable forest management should therefore consider using a range of retention patch sizes combined with varying levels of surrounding dispersed retention in harvest designs to achieve objectives for plant conservation. [ABSTRACT FROM AUTHOR]

The article focuses on research on effects of retention patterns and retention levels on vascular plants in boreal forests of Canada and mentions aggregated retention which supports plant communities to unharvested forest.

As boreal forests rapidly warm due to anthropogenic climate change, long‐term baseline community data are needed to effectively characterize the corresponding ecological changes that are occurring in these forests. The combined seasonal dynamics (SEADYN) and annual dynamics (ANNDYN) data set, which documents the vegetative changes in boreal forests during the snow‐free period, is one such source of baseline community data. These data were collected by George H. La Roi and colleagues in Alberta, Canada from 1980 to 2015 within permanent sampling plots established in the Hondo‐Slave Lake area (eight stands; 1980–2015) in central Alberta and the Athabasca Oil Sands (AOS) region (17 stands; 1981–1984) near Fort McMurray in northeastern Alberta. Various data were collected, with temporal and spatial coverage differing by data set. These data sets include, but are not limited to, cover of each identified vascular plant and bryoid (moss, liverwort, and lichen) species; forest mensuration; forest litter production; and soil temperature and moisture. Notably, permanent sampling plots were set up as a grid, which will facilitate analyses of spatial relations. These data can be used to analyze long‐term changes in seasonal dynamics and succession within boreal forest communities and serve as a baseline for comparison with future forest conditions in unmanaged, managed, and reclaimed forests. Data are released under a CC‐BY license; please cite this data paper when using the data for analyses. [ABSTRACT FROM AUTHOR]

Given the habitat moisture (air humidity or soil moisture) preferences of many forest bryophytes, we explored whether the depth-to-water (DTW) index, derived from remotely sensed Light Detection and Ranging (LiDAR) data, was related to fine-scale patterns of spatial variation in bryophyte abundance, diversity, and composition. The goal was to assess the utility of the topographic DTW index as a tool to decipher trends in bryophyte assemblages along a site wetness gradient in the boreal mixedwood forest. Discrete Airborne Laser Scanning (ALS) data were acquired over the entire Ecosystem Management Emulating Natural Disturbance (EMEND) experimental site located in northwestern Alberta, Canada (56° 46′ 13″ N, 118° 22′ 28″ W), based on which we calculated a mathematical index of approximate depth to water at or below the soil surface at 1 m resolution using the Wet-Areas Mapping model. Bryophytes (mosses and liverworts) were sampled in permanent sample plots in unmanaged forest stands of varying dominant canopy tree composition. The relationships between DTW and bryophyte cover, richness, diversity, and composition in broadleaf (deciduous)-, mixed, and conifer-dominated boreal forest stands were analyzed using linear mixed-effect models and multivariate analyses. Bryophyte cover was highest in conifer-dominated forest, which occupied the wetter end of the DTW gradient, followed by mixed forest, whereas broadleaf forest, which occupied the drier end of the DTW gradient, had the lowest cover but highest bryophyte diversity. Bryophyte cover in conifer-dominated forests was positively related to site moisture (negatively related to the DTW index). In contrast, bryophyte species richness and diversity were negatively related to site moisture (increased at higher DTW values) in all forest types. DTW explained significant variation in bryophyte species composition in mixed forests, while indicator species analysis identified species with preferences for wet, moist, and dry site conditions in each forest type. Our results corroborate the importance of site moisture as a driver of bryophyte assemblages but, interestingly, there were important differences among forest types, which themselves are distributed across a gradient of site moisture. Our study demonstrates the utility of the topographic DTW index for understanding fine-scale (plot-level) variation in bryophyte assemblages in forested landscapes. [ABSTRACT FROM AUTHOR]

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.)

Abstract: Question: What are the processes driving regeneration and successional pathways in Pinus contorta subsp. latifolia Douglas ex Loudon forests? Location: Canadian Rockies, Alberta, Canada. Methods: We used five 1‐ha long‐term permanent plots, dendrochronological stand reconstruction and detailed spatial analysis of stem‐mapped data. Results: Establishment of shade‐intolerant species mainly occurred within 20 years post‐fire but important later recruitment of these species was observed in the drier plots, primarily in gaps in stands that had more open canopies. Shade‐tolerant species established quickly following fires on moister sites but, despite apparent seed source availability after the stand‐initiating fire, their establishment was delayed in the drier sites, most likely due to moisture limitations. Shade‐tolerant regeneration was clustered around shade‐tolerant trees that had established immediately post‐disturbance; this suggests the latter served as seed sources and perhaps created favourable microsites for establishment. Conclusion: Competition for light, dispersal limitation and moisture limitations were all processes influencing regeneration and successional pathways in these P. contorta stands. Although initial studies in these stands had suggested some of the stands could potentially be self‐perpetuating P. contorta forests, our results suggest that all plots studied will likely transition towards dominance of shade‐tolerant species. However the rate of this transition will likely be slower in the drier sites compared to the moister sites since the density of shade‐tolerant regeneration was much lower in these sites and took longer to establish (ca. 70–90 years) post‐disturbance. [ABSTRACT FROM AUTHOR]

Abstract: Variable‐retention harvest is widely recognized as an alternative to more intensive methods such as clear‐cutting. However, present information is inadequate to judge the impact of variable retention on biodiversity of indigenous forest organisms intolerant of canopy removal, such as forest‐inhabiting bryophytes. We examined how bryophyte species cover, richness, diversity and composition change with time in response to a broad range of dispersed retention harvest treatments (2% [clear‐cut], 10%, 20%, 50%, 75% retention of original basal area) contrasted with uncut controls [100% retention]) in broadleaf deciduous, mixedwood and conifer‐dominated boreal forests in North West Alberta, Canada. Bryophytes were studied in 432 permanent sample plots within 72 compartments before harvest and at 3, 6 and 11 years after harvest. Clear‐cut and lower (10% and 20%) retention levels resulted in lower cover and richness of bryophytes than in unharvested control compartments in mixed and conifer‐dominated forests, but less so in deciduous‐dominated forests, which generally supported low cover and richness. Species composition in each forest type varied along the gradient of harvesting intensity; clear‐cuts and lower levels of retention supported similar composition, as did control plots and those representing higher retention levels. Over time, the retention harvest treatments became more similar to uncut controls. Synthesis and applications. Variable‐retention harvests can better maintain bryophyte biodiversity in managed boreal mixedwood forests, as compared to clear‐cuts. We found the efficacy of retention harvest scaled with harvest intensity. Higher levels of retention better moderated the negative impacts of harvesting on bryophyte assemblages across all forest types. Our results suggest, however, that even 10% retention will facilitate faster post‐harvest recovery of bryophytes, as compared to clear‐cutting. [ABSTRACT FROM AUTHOR]

The extent to which past states influence present and future ecosystem characteristics (ecosystem memory (EM)) is challenging to assess because signals of past ecological conditions fade with time. Using data about seven different taxa, we show that ecological gradients initiated by wildfires up to three centuries earlier affect biotic recovery after variable retention harvest in the boreal mixedwood forest. First, we show that fire history over the last 300 years is reflected in pre-harvest species-specific stand basal area (BA), with longer times since high severity fire associated with proportionally higher BA of shade-tolerant softwood species than shade-intolerant hardwoods. Second, using patterns in the BA of pre-harvest tree species we link fire history to species composition of pre-harvest assemblages of bryophytes, herbs, shrubs, regenerated trees, songbirds, spiders and carabid beetles. Finally, we use variance partitioning to compare the importance of species-specific pre- versus post-harvest BA for explaining the structure of these seven biotic assemblages two, five and ten years after harvest. We detected persistent significant effects of pre-harvest BA in all post-harvest biotic assemblages up to ten years after harvest. Pre-harvest BA was more strongly associated with early post-harvest understory plant and carabid beetle assemblages than was post-harvest BA, but the opposite was true for spiders, songbirds and regenerated trees. EM effects were detected two, five and ten years after harvest but temporal patterns varied according to taxa. Thus, EM of fire history can persist at least ten years after variable retention harvest and such effects appear to be stronger for understory plants than for animals. We conclude that management of biological legacies to increase post-disturbance EM will increase overall resilience and sustainability of these mixedwood forests. [ABSTRACT FROM AUTHOR]

The effects of different understorey management practices on tree-weed dynamics and associated tree establishment were investigated in newly planted hybrid poplar plantations containing Walker poplar (Populus deltoides × (P. laurifolia × P. nigra)) and its progeny Okanese poplar (Walker × (P. laurifolia × P. nigra)). Trees were established in 2012 on a research site in northeastern Alberta using one of four treatments: business as- usual (BAU; herbicide, tillage, then planting), extended fallow (BAU + additional tillage and herbicide before planting), a cover crop interseeded on BAU areas, and a no-till treatment where trees were planted directly into sod receiving prior chemical weed control but no tillage. Tree survival and growth, herbaceous vegetation cover and composition, soil conditions (N availability, water content and temperature), together with light availability, were measured over three consecutive growing seasons (2012-2014). Okanese outperformed Walker in all treatments and was more responsive to vegetation control, indicating greater plasticity and potential for short-rotation-intensive-culture plantations. Further, tree performance was improved by extended chemical and mechanical (fallow) site preparation prior to tree planting. This treatment resulted in sustained control of understorey vegetation, in particular competitive perennial forbs and graminoids, and increased light and nutrient availability to trees. These results also highlighted the importance of controlling perennial rather than annual herbaceous competitors prior to and during plantation establishment. [ABSTRACT FROM AUTHOR]

Copyright of Botany 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.)

Understanding processes driving mortality in forests is important for comprehension of natural stand dynamics and for informing natural disturbance-based ecosystem management. There has been considerable study of mortality in forests during the self-thinning phase but we know much less about processes driving mortality in stands at later successional stages. We addressed this through study of five 1-ha spatially explicit permanent plots in mature (111-186 yr old in 2012) Pinus contorta stands in the Canadian Rocky Mountains using data from repeated measurements over a 45-yr period, dendrochronological information, and point pattern analysis. We tested the hypothesis that these stands had completed the self-thinning/density-dependent mortality stage of succession. Contrary to our expectations, the self-thinning phase can persist for more than 140 yr following stand establishment. Our findings suggest this was attributable to prolonged post-fire establishment periods due to surface fires in three of the plots while in the other two plots moist conditions and slow growth most likely delayed the onset of competition. Several pieces of evidence indicated the importance of density-dependent mortality in these stands over the study period: (1) The diameter distribution of individuals changed from initially right-skewed toward normality as a result of mortality of smaller-diameter stems. (2) Individuals of lower canopy positions were proportionally more affected by mortality. (3) When compared to the pre-mortality pattern, surviving stems in all stands had an increasingly uniform spatial distribution. In two of the plots, recent windthrow and/or ingrowth initially hindered our ability to detect density-dependent mortality but our dendrochronological sampling and permanent plot data allowed us to untangle the different processes at play; in doing so we demonstrate for the first time how density-independent processes can mask underlying density-dependent mortality processes in older stands. Mortality of larger dominant canopy trees increased over the study period and mortality of dominant stems was a random process in all stands suggesting these stands were approaching the end of the self-thinning stage and that density-independent processes might soon become more important. Our results provide an improved understanding of mortality processes that can be applied to natural disturbance-based ecosystem management. [ABSTRACT FROM AUTHOR]

Knowledge of regeneration processes of the endangered whitebark pine ( Pinus albicaulis Engelm.) is critical for developing approaches for recovery and restoration of the species. We investigated biophysical associates of whitebark pine seedling occurrence and density in different mesohabitats (defined by community type and elevation) within the northern Rocky Mountains of Alberta. We developed candidate linear models to examine factors influencing occurrence and abundance. Occurrence was positively related to bare mineral soil and species richness in forest mesohabitats, while in both open and alpine-treeline environments it was positively related to prostrate shrub cover. Negative associates included tree cover, rocky substrates, and seedling cover of other conifers. Model validation showed a strong correlation between observed and predicted occurrence (correlations of 0.60, 0.56, and 0.56 for forest, open, and alpine-treeline mesohabitats, respectively). Climate models best predicted seedling density; abundance was highest on south-facing slopes in all mesohabitats. Correlations between observed and predicted density were 0.83, 0.92, and 0.72 for forest, open, and alpine-treeline mesohabitats, respectively. Our study identifies biophysical parameters to consider when planting blister rust-resistant seedlings and suggests that open mesohabitats along south-facing slopes may be best for regeneration of whitebark pine, particularly near the northern limits of its range. [ABSTRACT FROM AUTHOR]

Understory plant communities play critical ecological roles in forest ecosystems. Both above- and below-ground ecosystem properties and processes influence these communities but relatively little is known about such effects at fine (i.e., one to several meters within-stand) scales, particularly for forests in which the canopy is dominated by a single species. An improved understanding of these effects is critical for understanding how understory biodiversity is regulated in such forests and for anticipating impacts of changing disturbance regimes. Our primary objective was to examine the patterns of fine-scale variation in understory plant communities and their relationships to above- and below-ground resource and environmental heterogeneity within mature lodgepole pine forests. We assessed composition and diversity of understory vegetation in relation to heterogeneity of both the above-ground (canopy tree density, canopy and tall shrub basal area and cover, downed wood biomass, litter cover) and below-ground (soil nutrient availability, decomposition, forest floor thickness, pH, and phospholipid fatty acids (PLFAs) and multiple carbon-source substrate-induced respiration (MSIR) of the forest floor microbial community) environment. There was notable variation in fine-scale plant community composition; cluster and indicator species analyses of the 24 most commonly occurring understory species distinguished four assemblages, one for which a pioneer forb species had the highest cover levels, and three others that were characterized by different bryophyte species having the highest cover. Constrained ordination (distance-based redundancy analysis) showed that two above-ground (mean tree diameter, litter cover) and eight below-ground (forest floor pH, plant available boron, microbial community composition and function as indicated by MSIR and PLFAs) properties were associated with variation in understory plant community composition. These results provide novel insights into the important ecological associations between understory plant community composition and heterogeneity in ecosystem properties and processes within forests dominated by a single canopy species. [ABSTRACT FROM AUTHOR]

We tested whether direct placement of forest floor material ( FFM: litter, fibric, humus layers and surface mineral horizons) and sowing of a cover crop ( Melilotus officinalis) could facilitate the establishment of native forest understory species at a reclaimed coal mine in Alberta, Canada. FFM was salvaged at two depths (15 and 40 cm) from a recently harvested native aspen forest and immediately placed at the same depths on the reclamation site. Total richness (approximately 61 species in 96 subplots) was similar in each of 3 years post-placement; total richness for all 3 years combined was 87 including 34 typical boreal forest understory species plus 30 other natives. The deeper treatment reduced cover of all species, native and non-native species in year 1. In year 3, the deeper treatment still had lower cover of non-native species but had higher cover of forest understory species in years 2 and 3. The deeper treatment also resulted in lower species richness per plot, but only in year 1. In year 2 (when the biennial clover was at its tall stage), the cover crop treatment was associated with lower cover of non-native species but did not affect the cover of native forest understory species. Direct placement of FFM can help facilitate establishment of a diverse native boreal forest understory in a reclaimed landscape. Although richness and cover may be initially higher with shallower salvage and placement, deeper salvage may ultimately be better for encouraging establishment of native forest understory species. [ABSTRACT FROM AUTHOR]

Although anthropogenic edges are an important consequence of timber harvesting, edges due to natural disturbances or landscape heterogeneity are also common. Forest edges have been well studied in temperate and tropical forests, but less so in less productive, disturbance-adapted boreal forests., We synthesized data on forest vegetation at edges of boreal forests and compared edge influence among edge types (fire, cut, lake/wetland; old vs. young), forest types (broadleaf vs. coniferous) and geographic regions. Our objectives were to quantify vegetation responses at edges of all types and to compare the strength and extent of edge influence among different types of edges and forests., Research was conducted using the same general sampling design in Alberta, Ontario and Quebec in Canada, and in Sweden and Finland. We conducted a meta-analysis for a variety of response variables including forest structure, deadwood abundance, regeneration, understorey abundance and diversity, and non-vascular plant cover. We also determined the magnitude and distance of edge influence (DEI) using randomization tests., Some edge responses (lower tree basal area, tree canopy and bryophyte cover; more logs; higher regeneration) were significant overall across studies. Edge influence on ground vegetation in boreal forests was generally weak, not very extensive (DEI usually < 20 m) and decreased with time. We found more extensive edge influence at natural edges, at younger edges and in broadleaf forests. The comparison among regions revealed weaker edge influence in Fennoscandian forests., Synthesis. Edges created by forest harvesting do not appear to have as strong, extensive or persistent influence on vegetation in boreal as in tropical or temperate forested ecosystems. We attribute this apparent resistance to shorter canopy heights, inherent heterogeneity in boreal forests and their adaptation to frequent natural disturbance. Nevertheless, notable differences between forest structure responses to natural (fire) and anthropogenic (cut) edges raise concerns about biodiversity implications of extensive creation of anthropogenic edges. By highlighting universal responses to edge influence in boreal forests that are significant irrespective of edge or forest type, and those which vary by edge type, we provide a context for the conservation of boreal forests. [ABSTRACT FROM AUTHOR]

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Recreational activities in alpine areas have been increasing in recent decades, creating the need to improve our understanding of the impacts of these activities and how they are best managed. We explored impacts of recreational trail use on dry alpine meadows in the northern Canadian Rockies of Alberta. Data collected in 142 plots (0.5 m × 1 m) were used to compare plant community metrics among (1) a recreational trail, (2) intact tundra meadows (undisturbed), and (3) sparsely vegetated gravel steps formed by frost disturbance (naturally disturbed). As compared to undisturbed tundra, trails had substan-tially lower cover of vascular plants (4% vs. 35%), lichen (0% vs. 10%), and cryptogamic crust (0% vs. 4%); trails also had lower species richness (7 vs. 11 species per plot), but greater soil compaction (2.75 vs. 1.25 kg cm-2). Trails differed from natural gravel steps, which had three times more biotic cover and different composition. This highlights the difference in effects of human and natural disturbance. Positive feedback effects of tram-pling in tundra ecosystems may lead to altered environmental conditions, including de-creased infiltration capacity and nutrient cycles in soils, and more extreme temperatures at the soil surface. These feedbacks could inhibit regeneration of abandoned trails. [ABSTRACT FROM AUTHOR]

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Epiphytic mosses and liverworts contribute substantially to the bryophyte diversity of circumpolar boreal forests but are susceptible to altered growing conditions after forest harvesting. Management practices that retain some trees after harvest may enhance epiphyte survival; however, the effectiveness of this emerging method needs to be assessed. We examined the survival, composition, and nearest neighbour relationships of epiphytic bryophytes on trembling aspen (Populus tremuloides Michx.) across a range (10%–100%) of dispersed green-tree retention 5 years after harvest in boreal mixed-wood forest. Growth of the forest floor moss Hylocomium splendens (Hedw.) Schimp. in B.S.G. was used as an indicator of changes in moisture availability for epiphytes following harvesting. Epiphyte richness and abundance increased with canopy retention and were positively correlated with local abundance of coniferous trees. Positive associations among neighbouring species in intact forest demonstrated that interspecies relationships form naturally. However, there was a shift in species composition after harvesting and fewer interspecific associations with declining retention. These trends were accompanied by reduced Hylocomium splendens growth, which implies that moisture may be an important driver of epiphyte response. Although different levels of canopy retention were similarly capable of maintaining some epiphytes, the loss of species associated with intact forest will require consideration of alternative management practices for their conservation. Les mousses et les hépatiques épiphytes contribuent substantiellement à la diversité des bryophytes des forêts boréales circumpolaires, mais sont sensibles aux modifications des conditions de croissance, suite aux opérations forestières. Les méthodes d’aménagement qui conservent certains arbres après la récolte peuvent améliorer la survie des épiphytes; cependant, on doit évaluer l’efficacité de ces méthodes en émergence. Les auteurs ont examiné la survie, la composition et les relations avec les voisins les plus rapprochés des bryophytes épiphytes sur le peuplier faux-tremble (Populus tremuloides Michx.) pour l’ensemble d’une aire (10 % à 100 %) comportant des arbres vivants conservés et dispersés, 5 ans après la récolte dans une forêt boréale mixte. Ils ont utilisé la croissance d’une mousse du parterre forestier, l’Hylocomium splendens (Hedw.) Schimp. in B.S.G., comme indicatrice des modifications de la disponibilité de l’humidité pour les épiphytes, suite à la récolte des arbres. La richesse et l’abondance des épiphytes augmentent avec la rétention de la canopée et montrent des corrélations positives avec l’abondance localisée de conifères. Les associations positives avec les espèces avoisinantes dans la forêt intacte démontrent que des relations interspécifiques se forment naturellement. Cependant, on observe un déplacement de la composition en espèces après la récolte et moins d’associations interspécifiques avec une diminution de la rétention. Ces tendances s’accompagnent d’une réduction de la croissance de l’ Hylocomium splendens, ce qui implique que l’humidité pourrait être un agent causal important de la réaction des épiphytes. Bien que différents degrés de conservation de la canopée peuvent être également aptes à maintenir certaines épiphytes, la perte d’espèces associées aux forêts intactes nécessitera la définition de méthodes alternatives d’aménagement pour leur conservation. [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.)

Bryophyte diaspore banks are a potential source of reproductive propagules that may be able to colonize newly available habitat after forest harvesting. However, their role and the factors influencing the successful establishment of species remain poorly understood. To investigate these aspects of diaspore banks, we obtained mineral soil samples from mixed and coniferous stands of boreal mixed-wood forest in northern Alberta, Canada, which had recently experienced a range of harvesting intensities. Samples were germinated in growth cabinets under two light regimes. The composition of germinated bryophyte species was compared among forest types, harvesting intensities, and light levels, and also related to edaphic conditions and geographic location of the sample site. Germinated species composition was not related to forest type or harvesting intensity, but was associated with measured edaphic variables and geographic space, indicating that similarity in species composition reflected similarity in edaphic conditions and spatial proximity. This was partly because of spatial dependence of edaphic variables. Light intensity had a significant influence on the development of species assemblages and individual species responses. Richness and cover of acrocarpous mosses (fugitive, colonist, and shuttle life-history strategies) were significantly reduced under low light conditions, but pleurocarpous mosses (perennial strategy) were not affected. Shannon diversity and the frequency of reproduction were significantly greater with high light. Pleurocarpous mosses that are characteristic of intact forests germinated frequently, suggesting that diaspore banks may influence their recovery after disturbance. Diaspore banks are a repository of species at sites affected by forest harvesting; however, diaspore germination and establishment will be constrained by the local environment, including edaphic conditions and light intensity. [ABSTRACT FROM AUTHOR]

Question: What is the disturbance response of low-arctic plant communities two to three decades after seismic exploration. Location: Mackenzie River Delta, low-arctic, northwestern Canada. Methods: Plant communities in two upland tundra vegetation types were compared between winter seismic lines, created between 1970 and 1986, and adjacent 'reference' tundra. Also, we used aerial surveys to quantify the total area impacted by visible linear features. Results: Vascular plant cover was significantly higher, and lichen cover significantly lower, on seismic lines than in reference tundra. The increase in vascular plant cover was attributable to deciduous shrubs and graminoids. There were significant differences in plant community composition between seismic lines and reference tundra but no differences in species diversity or richness. Betula glandulosa and Arctagrostis latifolia were significant indicator species for seismic lines, while Saussurea angustifolia was a significant indicator for reference tundra. Based on the aerial surveys, these effects apply to at least 90% of seismic lines from two-dimensional programs in these habitat types during the 1970s. Conclusions: Vegetation composition and structure on 20-30-year-old seismic lines differs from reference upland tundra despite no persistent differences in organic layer depth or depth to permafrost. We propose that this reflects: (1) successional redevelopment following changes in soil conditions and nutrient availability arising from the disturbance, and/or (2) disturbance-initiated succession towards a community reflecting current climatic conditions. [ABSTRACT FROM AUTHOR]

We studied effects of oil and gas exploration, using the most recent seismic exploration technologies, on tundra plant communities and soils in four vegetation types in the Low Arctic of western Canada, two to three years post-disturbance. For all four vegetation types, seismic lines had less vascular plant cover and more bare ground than adjacent "reference" tundra. For the two upland tundra vegetation types, mosses and lichens were less abundant on seismic lines than in reference plots. There were no apparent differences in organic layer thickness between seismic lines and reference areas, but active layer depth (at the time of sampling) was significantly greater on seismic lines for the upland tundra and one of the wetland vegetation types. Diversity and richness were lower, and community composition was different, on seismic lines (as compared to reference plots) in upland tundra vegetation types but not in wetland types. The results suggest that (1) upland vegetation types are less resistant to seismic disturbance, (2) active layer depth increases following seismic disturbance, and (3) impacts from modern seismic techniques in upland tundra are similar to, or somewhat greater than, the initial impacts observed from the earliest phases of winter exploration ∼30 years ago. [ABSTRACT FROM AUTHOR]

We characterized the ectomycorrhizae (ECM) of planted white spruce (Picea glauca (Moench) Voss) seedlings as affected by mechanical site preparation (MSP) of clear-cut conifer-dominated boreal mixedwood forest. Relative abundance, richness, and composition of the ECM community were compared among untreated control, mixed, mounded, and scalped site preparation treatments. On >11 000 root tips, we observed 16 ECM morphotypes. Those common to the nursery in which the seedlings were raised were most abundant (Thelephora americana, Wilcoxina-like (E-strain), Amphinema byssoides, Phialocephala-like (MRA)). Seedlings in the untreated controls had lower abundances of these, but higher abundances of other ECM, which were not present in the nursery of origin but were indigenous to these forest stands. In terms of ECM composition, the “mixed” treatment was most similar to the untreated control, while the “scalped” and “mound” treatments showed significantly different ECM communities than the controls. Our results suggest that MSP may facilitate continued dominance by ECM that establish on seedlings in the nursery while slowing the natural succession towards the natural forest ECM. MSP treatments that leave some surface organic matter relatively intact may impact ECM less than those that remove or bury the organic layer. Nous avons caractérisé les ectomycorhizes (ECM) de plants d’épinette blanche (Picea glauca (Moench) Voss) affectés par la préparation mécanisée de terrain (PMT) à la suite d’une coupe à blanc dans une forêt mixte dominée par des résineux. L’abondance relative, la richesse et la composition de la communauté d’ECM a été comparée entre un témoin non traité et des traitements de préparation de terrain mixtes, d’aménagement de buttes et de scalpage. Nous avons observé 16 morphotypes d’ECM sur plus de 11 000 apex racinaires. Ceux qui étaient communs dans la pépinière où les semis avaient été produits étaient les plus abondants (Thelephora americana, le type Wilcoxina (souche E), Amphinema byssoides, le type Phialocephala (MRA)). L’abondance de ces ECM était plus faible chez les semis des témoins non traités qui comportaient, cependant, une plus forte abondance d’autres ECM qui n’étaient pas présentes dans la pépinière d’origine, mais qui étaient indigènes à ces peuplements forestiers. En termes de composition en ECM, le traitement mixte était le plus semblable au témoin non traité alors que le scalpage et l’aménagement de buttes étaient associés à des communautés d’ECM significativement différentes de celle du témoin. Nos résultats indiquent que la PMT peut faciliter le maintien de la dominance des ECM établies sur les plants en pépinière tout en ralentissant la succession naturelle vers les ECM de la forêt naturelle. Les traitements de PMT qui laissent des superficies relativement intactes de matière organique peuvent avoir moins d’impact sur les ECM que ceux qui enlèvent ou enfouissent la couche de matière organique. [ABSTRACT FROM AUTHOR]

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The simultaneous influence from multiple edges on remnant forest patches (such as wildlife corridors, protection buffers, small unharvested remnants or corners of larger patches) in harvested forest landscapes could impair, or possibly enhance, their effectiveness. When multiple edges are in close proximity, there may be interactions of edge influence such that the observed response is greater or less than would result from the influence of either edge alone. We examined possible ways in which two nearby forest edges of similar or different types might interact in terms of their influence on forest structure. We present an ‘edge interaction’ model for three possible types of interaction of edge influence: (1) no interaction, edge influence is limited to the strongest influence from either edge, (2) positive interaction, observed edge influence is greater than from either edge alone; (3) negative interaction or resistance, the influence from both edges is less than from a single edge (e.g., an older edge is resistant to effects from a younger edge). Empirical data for forest structure at the edges of cutblocks (harvested areas) and water bodies were entered into the models to predict edge influence in narrow forest corridors assuming the null hypothesis of no interaction. Randomization tests were used to compare predictions to observed edge influence on recently-fallen logs and Populus spp. ( P. tremuloides Michx. and P. balsamifera L.) sapling density in lakeshore buffers in boreal mixedwood forest as well as on canopy cover and log, tree and snag abundance in riparian buffers and forested corridors separating cutblocks in Picea mariana (Mill.) BSP. forest. In lakeshore buffers, there was evidence of both positive and negative interaction at different locations within the buffer or at different times since buffer creation for both the abundance of logs and Populus sapling density. Trends suggested positive interaction for canopy cover and live tree density in riparian buffers and cutblock separators, and for snag density near the cut edges of riparian buffers. Testing hypotheses arising from our model of interaction of edge influence could lead to a clearer understanding of edge influence in fragmented landscapes. [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.)

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.)

Copyright of Canadian Journal of Botany 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.)