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A combination of wildfires and defoliating insect outbreaks play an important role in the natural successional dynamics of North American boreal mixedwood forests, which, in the long term, change the post‐disturbance composition and structure of forest stands. After stand‐replacing disturbances (mainly wildfires), early successional hardwoods typically dominate the affected areas. Provided enough time following disturbances, the increasing recruitment of mid‐ to late‐successional softwoods as well as the mortality of hardwoods gradually change forest composition from hardwoods to admixtures of hardwood‐conifer species and conifer‐dominated stands in mid and late successional stages, respectively. Such mixedwoods are abundant across the southern Canadian boreal forest. In boreal Canada, mixedwoods are the most structurally heterogeneous forest ecosystems, are highly productive, and form an important source of timber supply. Here we present the EASTERN BOREAL MIXEDWOODS CANADA data set, which documents the changes in composition and structure of stands originating from eight different wildfires representing a chronosequence of 249 yr since fire in eastern Canada. This data set has been used in several different projects to study and model the influence of natural (e.g., insect outbreaks) and anthropogenic disturbances (e.g., harvesting) on the dynamics of post‐fire stands. The data set covers a high range of variability in stand composition and structure, explained by species establishment, dominance, and mixture. It thus constitutes a useful source of information to trace the dynamics of the main boreal tree species of eastern North America, from their establishment to their replacement at different spatial scales (e.g., from stand to landscape level). Please cite this data paper when the data are used in publications. We also request that researchers and teachers inform us of how they are using the data. We are open to collaborate in developing or co‐authoring relevant research projects based on this data set. [ABSTRACT FROM AUTHOR]

Aim Feedbacks between climate warming and fire have the potential to alter Arctic and sub-Arctic vegetation. In this paper we assess the effects and interactions of temperature and wildfire on plant communities across the transition between the Arctic and sub-Arctic. Location Mackenzie Delta region, Northwest Territories, Canada. Methods We sampled air temperatures, green alder ( Alnus viridis ssp. fruticosa) cover, growth, reproduction and age distributions, and overall plant community composition on burned and unburned sites across a latitudinal gradient. Results Mean summer temperature across the study area decreased by 3 °C per degree of increasing latitude (6 °C across the study area). In the northern part of the study area, where seed viability was low, alder was less dominant than at southern sites where seed viability was high. The age structure of alder populations across the temperature gradient was highly variable, except in the northern part of the forest–tundra transition, where populations were dominated by young individuals. Alder growth and reproduction were significantly greater on burned sites (38–51 years following fire) than on unburned sites. North to south across the temperature gradient, vegetation changed from a community dominated by dwarf shrubs and fruticose lichens to one characterized by black spruce ( Picea mariana), alder and willows ( Salix spp.). Regardless of the position along the temperature gradient, burned sites were dominated by tall shrubs. Main conclusions Temperature limitation of alder abundance and repro-duction, combined with evidence of recent recruitment on unburned sites, indicates that alder is likely to respond to increased temperature. Elevated alder growth and reproduction on burned sites shows that wildfire also has an important influence on alder population dynamics. The magnitude of alder’s response to fire, combined with observations that burns at the southern margin of the low Arctic are shrub dominated, suggest that increases in the frequency of wildfire have the potential to alter northern vegetation on decadal scales. By creating new seedbeds, fire provides opportunities for colonization that may facilitate the northward movement of tall shrubs. Feedbacks between the global climate system and low Arctic vegetation make understanding the long-term impact of increasing fire frequency critical to predicting the response of northern ecosystems to global change. [ABSTRACT FROM AUTHOR]

Canada geese (Branta canadensis) migrating along coastal flyways are reliant on natural coastal ecosystems. Within these stopover sites, eelgrass (Zostera marina), the most common and widespread seagrass species in North America, is an important food resource for migrating waterfowl. Given the growing anthropogenic pressure on coastal ecosystems, geese migrating along coastal regions may find it increasingly difficult to access suitable stopover sites where food is abundant and human disturbance is low. We assessed the influence of hunting and eelgrass on the spatiotemporal distribution of Canada geese in the Tabusintac Bay, New Brunswick, Canada, a wetland of international importance. We surveyed Canada geese at 6 stations from mid‐September to late October, 2016 and 2017. We used 2‐part hurdle models consisting of generalized linear mixed models with binomial and negative binomial response distributions to model Canada geese presence and abundance, respectively, in relation to eelgrass abundance, distance to the mainland coastline, water depth, and tidal conditions in 3 different hunting intensity periods. Eelgrass abundance is a significant predictor of Canada geese presence early in the season, when hunting activity is low. At the onset of the hunting period, geese shifted diurnal distribution to areas farther offshore, indicating a response to avoid disturbance, and the abundance of Canada geese increased with increasing eelgrass availability, emphasizing the importance of eelgrass as a food source during fall migration in that region. Thus, our results highlight the effects of human disturbance and eelgrass abundance in influencing stopover behavior of Canada geese during fall migration in eastern Canada. [ABSTRACT FROM AUTHOR]

Peatlands store carbon (C), nitrogen (N), and phosphorus (P), and the stoichiometric relationship among them may be modified by ecosystem disturbances, with major implications for boreal peatland ecosystem functions. To understand the potential impact of landscape fragmentation on peatland nutrient stoichiometry, we characterize the stoichiometric ratios of C, N and P in the soil–plant systems of disturbed boreal forest peatlands and also assessed relationships among site conditions, nutrient availability, stoichiometric ratios (C:N:P) and C storage in four sites that represent the forms of disturbed peatlands in the Athabasca oil sands region. Our results showed that nutrient stoichiometric balance differed across and within these peatlands, among plants, peat, and groundwater. Ratios of C:N and C:P in peat is a function of nutrient and moisture conditions, increasing from nutrient-rich (C:N = 28; C:P = 86) to nutrient-poor fens (C:N = 82; C:P = 1061), and were lower in moist hollows relative to drier hummock microforms. In groundwater, the drier nutrient-rich fen had higher N:P ratios relative to the nutrient-poor fen, reflecting interactions between dominant hydrologic conditions and stoichiometric relationships. The N:P ratio of plants was more similar to those of peat than groundwater pools, especially in the most recently disturbed nutrient-poor fen, where plant C:N:P ratios were greater compared to older disturbed sites in the region. These findings suggest that disturbances that modify moisture and nutrient regimes could potentially upset the C:N:P stoichiometric balance of boreal forest peatlands. It also provides valuable insights and essential baseline data to inform our understanding of how peatland C:N:P stoichiometry would respond to disturbance and restoration interventions in a boreal forest region at the tipping point of environmental change. [ABSTRACT FROM AUTHOR]

In the Canadian Western Boreal Plain (WBP), wetlands (ponds and peatlands) comprise up to 50% of the landscape and represent unique habitat where summer precipitation is often outpaced by evapotranspiration and hillslope groundwater position does not follow topography. In this sub-humid location, groundwater fluxes and stores in riparian peatlands influence pond water levels and root zone moisture sources for forested uplands. To accurately describe the transport and retention of water in peat, it is important to consider peat subsidence. This paper quantifies the amount and effect of seasonal subsidence in a riparian peatland in the Utikuma Lake region in north-central Alberta, Canada. Results demonstrate that the deep and poorly decomposed peat deposits are resistant to compression, and that thick (and persistent) ground frost hinders pore collapse (shrinkage) above the water table until late summer when the ground has thawed. Even then, subsidence is still limited to the top 50 cm and is not closely related to changes in peatland water table or pond water level. Thus the water balance of these ponds and riparian areas appears to be less sensitive to peat volume changes than it is to the persistence of a substantial frost layer well into the snow-free period. [ABSTRACT FROM AUTHOR]

Natural disturbances, such as fire and insect outbreaks, play important roles in natural forest dynamics, which are characterized over long time scales by changes in stand composition and structure. Individual-based forest simulators could help explain and predict the response of forest ecosystems to different disturbances, silvicultural treatments, or environmental stressors. This study evaluated the ability of the SORTIE-ND simulator to reproduce post-disturbance dynamics of the boreal mixedwoods of eastern Canada. In 1991 and 2009, we sampled all trees (including seedlings and saplings) in 431 (256 m2) plots located in the Lake Duparquet Research and Teaching Forest (western Quebec). These plots were distributed in stands originating from seven wildfires that occurred between 1760 and 1944, and which represented a chronosequence of post-disturbance stand development. We used the 1991 inventory data to parameterize the model, and simulated short- to long-term natural dynamics of post-fire stands in both the absence and presence of a spruce budworm outbreak. We compared short-term simulated stand composition and structure with those observed in 2009 using a chronosequence approach. The model successfully generated the composition and structure of empirical observations. In long-term simulations, species dominance of old-growth forests was not accurately estimated, due to possible differences in stand compositions following wildfires and to differences in stand disturbance histories. Mid- to long-term simulations showed that the secondary disturbance incurred by spruce budworm did not cause substantial changes in early successional stages while setting back the successional dynamics of middle-aged stands and accelerating the dominance of white cedar in late-successional post-fire stands. We conclude that constructing a model with appropriate information regarding stand composition and disturbance history considerably increases the strength and accuracy of the model to reproduce the natural dynamics of post-disturbance boreal mixedwoods. [ABSTRACT FROM AUTHOR]

Northern peatlands store globally significant amounts of soil carbon that could be released to the atmosphere under drier conditions induced by climate change. We measured forest floor respiration (RFF) at hummocks and hollows in a treed boreal bog in Alberta, Canada and partitioned the flux into aboveground forest floor autotrophic, belowground forest floor autotrophic, belowground tree respiration, and heterotrophic respiration using a series of clipping and trenching experiments. These fluxes were compared to those measured at sites within the same bog where water-table (WT) was drawn down for 2 and 12 years. Experimental WT drawdown significantly increased RFF with greater increases at hummocks than hollows. Greater RFF was largely driven by increased autotrophic respiration driven by increased growth of trees and shrubs in response to drier conditions; heterotrophic respiration accounted for a declining proportion of RFF with time since drainage. Heterotrophic respiration was increased at hollows, suggesting that soil carbon may be lost from these sites in response to climate change induced drying. Overall, although WT drawdown increased RFF, the substantial contribution of autotrophic respiration to RFF suggests that peat carbon stocks are unlikely to be rapidly destabilized by drying conditions. [ABSTRACT FROM AUTHOR]

Corresponding with the increasing global resource demand, harvesting now affects millions of hectares of boreal forest each year, and yet our understanding of harvesting impacts on boreal carbon (C) dynamics relative to wildfire remains unclear. We provide a direct comparison of C stocks following clearcut harvesting and fire over a 27-year chronosequence in the boreal forest of central Canada. Whereas many past studies have lacked measurement of all major C pools, we attempt to provide complete C pool coverage, including live biomass, deadwood, forest floor, and mineral soil C pools. The relative contribution of each C pool to total ecosystem C varied considerably between disturbance types. Live biomass C was significantly higher following harvesting compared with fire because of residual live trees and advanced regeneration. Conversely, most live biomass was killed following fire, and thus post-fire stands contained higher stocks of deadwood C. Snag and stump C mass peaked immediately following fire, but dramatically decreased 8 years after fire as dead trees began to fall over, contributing to the downed woody debris C pool. Forest floor C mass was substantially lower shortly after fire than harvesting, but this pool converged 8 years after fire and harvesting. When total ecosystem C stocks were examined, we found no significant difference during early stand development between harvesting and fire. Maximum total ecosystem C occurred at age 27 years, 185.1 ± 18.2 and 163.6 ± 8.0 Mg C ha for harvesting and fire, respectively. Our results indicate strong differences in individual C pools, but similar total ecosystem C after fire and clearcutting in boreal forests, and shall help improve modeling terrestrial C flux after stand-replacing disturbances. [ABSTRACT FROM AUTHOR]

Copyright of Environmental Reviews 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 Environmental Reviews 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.)

The 'Natural Disturbance Paradigm' for forest management seeks to meet conservation goals by modeling industrial harvest in fire-driven forest systems on patterns associated with wildfire. Fire suppression and increased forest harvesting may have detrimental effects on biodiversity, and therefore prescribed burning is suggested to retain legacies of wildfire not emulated under natural disturbance based approaches. The merits of this approach are being tested in the EMEND experiment in the Canadian boreal mixedwood forest. We compared responses of ground-dwelling spiders between sites subjected to prescribed post-harvest burning and retention harvest during three seasons during the first 7 years after disturbance. Overall, 38,661 adult spiders representing 190 species were collected. Estimated species richness was highest in undisturbed sites in all 3 years. Burning had the strongest negative effect on species richness 1-2 years after treatment; however, richness was higher in burns than in harvested sites 5-6 years post-disturbance. Species turnover was highest within controls but tended to increase over time between burned and harvested plots. Lower turnover in burned and harvested sites may reflect habitat homogenization by disturbance, suggesting a management and conservation challenge in relation to naturally disturbed and undisturbed areas. Species were grouped into disturbance-specialists, disturbance-tolerant, disturbance-generalists and generalists; 22 species were significant indicators for untreated sites, 18 for the burn and three for the harvest treatments. No major differences were observed in the spider fauna between harvested and burned areas within the first 6-7 years post-disturbance, and little evidence of recovery toward the pre-harvest fauna was evidenced. However, long term experiments may improve understanding of natural disturbance processes and improve management of boreal forests. [ABSTRACT FROM AUTHOR]

Relative to their cultivated surroundings, sandhills of the Canadian prairies represent intact, heterogeneous ecosystems. These extensive tracts of sand dunes and native prairie are biodiversity hotspots, which act as refugia for a variety of specialized wildlife species. However, due to changes in climate and suppression of natural disturbance, the dunes have experienced drastic rates of stabilization over the past 200 years, such that the proportion of open sand in the region is currently less than 1%. This continuing trend is resulting in a gradual loss of sparsely vegetated, sandy habitat for many uncommon, specialist species, including a number that are considered to be at risk of extirpation or extinction by COSEWIC (Canada's list agency). Without management to conserve active sandhill habitat the future long-term survival of rare and imperilled dune-dependent plants and animals is questionable. In this article we propose that the re-introduction of disturbance to southern Canadian prairie sandhills, specifically sandhill use by bison, might be effective in restoring and sustaining actively-eroding sandhill habitat to support some threatened and endangered species. We outline several lines of evidence (geological, geomorphological, archaeological, and historical accounts) indicating bison occupied sandhills and actively modified these ecosystems until European settlement of the prairies. We argue that bison were attracted to sandhills for a number of reasons, and that in great numbers they had considerable influence on sandhills ecosystem functions. Behaviours such as grazing, trailing, wallowing, horning, and trampling created a patchwork mosaic of disturbance effects. We hypothesize that it may be beneficial to reintroduce bison to sandhills ecosystems in the Canadian prairies to restore biodiversity at all levels. [ABSTRACT FROM AUTHOR]

Biodiversity is a multifaceted concept that often eludes simple operational definitions. As a result, a variety of definitions have been proposed each with varying levels of complexity and scope. While different definitions of biodiversity exist, the basic unit of measurement for the vast majority of studies is conducted at the species level. Traditional approaches to measuring species richness provide useful, yet spatially constrained information. Remote sensing offers the opportunity for large area characterizations of biodiversity in a systematic, repeatable, and spatially exhaustive manner. Based on this review we examine the potential for a national biodiversity monitoring system for Canada driven by remote sensing, a country approaching 1 billion ha in area, with the aim of producing recommendations that are transferable for regional or continental applications. A combination of direct and indirect approaches is proposed, with four selected key indicators of diversity that can be derived from Earth observation data: productivity, disturbance, topography, and land cover. Monitoring these indicators through time at an ecosystem level has the potential to provide a national early warning system, indicating where areas of potential biodiversity change may be occurring. We believe the large area biodiversity monitoring system as outlined would provide an initial stratification of key areas where regional and local scale analysis can be focused, while also providing context-specific information for species collection data. [ABSTRACT FROM AUTHOR]

Copyright of Environmental Reviews 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.)

1. The stage-specific responses of eruptive populations to ecosystem alterations have received little attention, despite the relevance of the issue for conservation biology and pest management. This study examined the hypothesis that forest thinning treatments affect the outbreak cycles of Neodiprion abietis, a sawfly defoliator. 2. The densities of eggs, early instar larvae, late-instar larvae, cocoons and adults of N. abietis were monitored during an outbreak in a thinned and an adjacent untreated stand at each of three sites in western Newfoundland, Canada. 3. The amplitude of population fluctuations was greater in thinned than in adjacent untreated stands at certain points in the increasing or peaking stages of N. abietis outbreaks for all life stages sampled. However, the timing and magnitude of differences in fluctuations attributed to thinning varied among the life stages of N. abietis. 4. The largest difference between stand types occurred in the generation preceding peak egg density, when adult densities were three times higher in thinned than untreated stands. Conversely, only moderate differences in egg density between stand types were observed in the following generation. Combined with the observation that the modes of population fluctuations occurred earlier in thinned stands, this suggests that adult dispersal resulted in a redistribution of eggs between thinned and untreated stands. 5. Synthesis and applications. To our knowledge, this is the first study to show that silvicultural practices involving a reduction in forest stand density may alter the outbreak cycles of an eruptive population, potentially increasing the severity of outbreaks in treated, as well as in adjacent untreated, stands. Hence, this study emphasizes the need to consider proactively the potential impact of silvicultural practices on species such as N. abietis, which are most abundant in low-density stands. This field study also demonstrates that the response to ecosystem alteration of an outbreak population can vary with the different life stages of the studied organism, indicating that the detection of the impact of ecosystem alterations on a population can depend on the life stage sampled. [ABSTRACT FROM AUTHOR]

Abstract Restoration of degraded natural vegetation in parks is often complicated by the need to maintain public access. We tested whether the natural canopy species, Thuja occidentalis , can be restored to degraded cliff edges in Bruce Peninsula National Park, Ontario, Canada without reductions in visitor numbers. Eighty 10-year-old and 80 4-year-old container-grown saplings and 1,400 seeds were planted and monitored for 4 years. Eight treatments were applied that tested for effects of planting site (distance from cliff edge and pathways) and supportive measures (soil, water, cages, or signs) on survival, growth, and damage. No trees became successfully established from seed. Younger trees showed faster initial establishment and growth, but 4-year survival was the same for both age groups (39%). Supplemental soil improved the health of planted trees, and both soil and water slightly improved their survival. Cages did not affect survival and growth but decreased damage to 4-year-old trees and increased it for 10-year-olds. Signs had no effect on any measured variable. Trees planted away from the cliff edge and from pathways had the greatest establishment success, 4-year survival, and general health. Relative visitor density, as estimated from spot counts of visitors, had the largest effect on restoration success; the results suggest a threshold of visitor density above which restoration may be impossible. Planting location, especially with respect to shade, was also important. The planting of 4-year-old trees without supportive measures is suggested as the most cost-effective restoration technique at this site. The results indicate that restoration of open woodland habitats is possible without total visitor exclusion but that some restrictions on visitor numbers or activities are necessary. [ABSTRACT FROM AUTHOR]

The sensitivity of soil landscapes to climatic variability and hydroclimatic events can be expressed as a landscape change safety factor, the ratio of potential disturbance to resistance to change. The use of a geographic information system (GIS) enables the spatially-explicit modeling of landscape sensitivity, but also raises the risk of violating the characteristic scales of disturbance and resistance, because the GIS technically simplifies the extrapolation of models, and associated concepts, to landscapes and scales not represented by the digital data base. Embedding landscape sensitivity into hierarchy theory, the formal analysis of the hierarchical structure of complex systems, provides a conceptual framework for the transfer of models and variables among landscape scales. In the subhumid southern Canadian plains, major hydroclimatic events (strong winds, intense rain, rapid snow melt) cause much of the physical disturbance of soil landscapes and terrestrial ecosystems. Prolonged dry or wet weather influences the resistance of soil and vegetation to these events. The potential disturbance of soil landscapes therefore can be derived from the probabilities of extreme events and seasonal conditions, as recorded in instrumental and proxy climate records. This time series analysis can be linked to the modeling of landscape sensitivity by establishing the probabilities of hydroclimatic events and climatic conditions which may exceed or lower the resistance of individual soil landscapes. [ABSTRACT FROM AUTHOR]

Mosses and hepatics (bryophytes) are the most diverse and abundant understorey vegetation within the Coastal Western Hemlock (CWH) and Interior Cedar–Hemlock (ICH) zones of British Columbia. This study intensively sampled bryophytes in 287 young- and old-growth stands in the CWH and ICH zones. Two major variables strongly influence the patterning of bryophyte diversity in these zones: stand age and habitat heterogeneity. Canonical correspondence analyses (CCA) identified these as the most important variables explaining stand–environment interactions. Alpha diversity is much greater in old-growth forests and beta diversity is high between young and old forests. Old-growth cedar–hemlock forests have between 60 (ICH) and 100% (CWH) more species than younger forests disturbed by wildfire in the ICH zones or logging in the CWH zones. Furthermore, a stand classification built on species composition partitioned species into stands of different ages and mesohabitat heterogeneity. Beta diversity was also partitioned between stands of different ages and habitat heterogeneity. This indicates that both young and old forests have a unique assemblage of species. Indicator analysis was used to choose a partial lists of species that are indicators of "old growthness". These old forests support a rich flora of hepatics and rare western North American endemics. High environmental continuity is associated with the most humid watersheds and cedar–hemlock forests within these watersheds have the highest bryophyte diversity. The establishment of rich communities of bryophytes in the moist cedar–hemlock forest has been occurring over the last 2000–7000 years, with the coastal rainforest much older than the inland rainforest. Large-scale disturbance, such as forestry, threatens the existence of these highly diverse communities. A better understanding of the patterning of bryophyte diversity will provide an opportunity to minimize the impact of forest operations on biodiversity. Bryophyte diversity in British Columbia cedar–hemlock forests will be sustained through ecosystem management of old-growth legacies (i.e., landscapes, stands, and their components) and preservation of areas of high diversity. Temporal and habitat variables are influential in the patterning of bryophyte diversity. Management plans that consider these variables will be better equipped to manage cedar–hemlock forests for maintaining biodiversity. Key words: biodiversity, bryophytes, cedar–hemlock, CWH, disturbance, ecosystem management, floristic habitat sampling, forest conservation, ICH, old growth, patterning of diversity, rare species, species richness.Les mousses et les hépatiques (bryophytes) représentent la végétation de sous-étage la plus diversifiée et abondante dans la zone côtière de la pruche de l'Ouest (CWH) et la zone à thuya et à pruche de l'Intérieur (ICH) en Colombie-Britannique. Cette étude a comporté un échantillonnage intensif des bryophytes dans 287 peuplements jeunes et anciens de ces deux zones. Deux variables y exercent une influence majeure sur le patron de répartition de la diversité des bryophytes : l'âge des peuplements et l'hétérogénéité des habitats. Des analyses canoniques des correspondances (ACC) ont indiqué qu'il s'agissait des plus importantes variables pour expliquer les interactions peuplement–environnement. La diversité alpha est beaucoup plus grande dans les forêts anciennes, et la diversité bêta est élevée entre les forêts jeunes et les forêts vieilles. Les forêts anciennes de thuya et de pruche comptent entre 60 % (ICH) et 100 % (CWH) plus d'espèces que les forêts plus jeunes perturbées par un incendie dans la zone ICH ou une récolte dans CWH. De plus, une classification des peuplements reposant sur la composition en espèces a fourni une répartition de la richesse en espèces entre peuplements ayant différentes caractéristiques d'âge et d'hétérogénéité des mesohabitats. La diversité bêta a aussi été répartie entre peuplements ayant différentes caractéristiques. Il ressort que la jeune forêt et la vieille forêt ont toutes deux un assemblage unique d'espèces. Une analyse a été effectuée pour établir une liste partielle d'espèces indicatrices d' « ancienneté ». Les vieilles forêts étudiées abritent une flore riche en hépatiques et en espèces endémiques rares de l'Ouest de l'Amérique du Nord. Une grande continuité de l'environnement est associée aux bassins versants les plus humides, et les forêts de thuya et de pruche de ces bassins renferment la plus forte diversité en bryophytes. L'établissement de riches communautés de bryophytes dans la forêt humide de thuya et de pruche se poursuit depuis des milliers d'années, de 2000 à 7000 ans, la forêt ombrophile côtière étant beaucoup plus âgée que la forêt ombrophile intérieure. Les perturbations de grande échelle, comme l'exploitation forestière, menacent l'existence de ces communautés de grande diversité. Une meilleure compréhension du patron de répartition de la diversité des bryophytes aidera à limiter l'impact des opérations forestières sur la biodiversité. La diversité des bryophytes dans les forêts de thuya et de pruche de la Colombie-Britannique pourra être maintenue en aménageant à l'échelle de l'écosystème les vestiges des forêts anciennes (c.-à-d. paysages, peuplements et leurs composantes) et en préservant des zones à forte diversité. Des variables temporelles et des variables de l'habitat influent sur le patron de répartition de la diversité des bryophytes. Les plans d'aménagement prenant en considération ces variables seront mieux en mesure d'assurer le maintien de la biodiversité des forêts de thuya et de pruche. Mots clés : aménagement écosystémique, biodiversité, bryophytes, conservation de la forêt, CWH, échantillonnage floristique de l'habitat, espèces rares, forêt ancienne, ICH, patron de répartition de la diversité, perturbation, pruche, richesse en espèces, thuya.[Traduit par la rédaction] [ABSTRACT FROM AUTHOR]

The Intergovernmental Panel on Climate Change (IPCC) has developed guidelines to standardize the international reporting of greenhouse gas emissions and removals by signatory nations of the UN Framework Convention on Climate Change. With regard to forest sector carbon fluxes, the IPCC guidelines require only that those fluxes directly associated with human activities (i.e., harvesting and land-use change) be reported. In Canada, the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS2) has been used to assess carbon fluxes from the entireforest sector. This model accounts for carbon fluxes associated withboth anthropogenic and natural disturbances, such as wild fires and insects. We combined model results for the period 1985 to 1989 with additional data to compile seven different national carbon flux inventories for the forest sector. These inventories incorporate different system components under a variety of seemingly plausible assumptions,some of which are encouraged refinements to the default flux inventory described in the IPCC guidelines. The resulting estimated net carbon fluxes varied from a net removal of 185,000 kt carbon per year of the inventory period to a net emission of 89,000 kt carbon per year. Following the default procedures in the IPCC guidelines, while using the best available national data, produced an inventory with a net removal of atmospheric carbon. Adding the effect of natural disturbances to that inventory reversed the sign of the net flux resulting in a substantial emission. Including the carbon fluxes associated with root biomass in the first inventory increased the magnitude of the estimated net removal. The variability of these results emphasizes the need for a systems approach in constructing a flux inventory. We argue that the choice of which fluxes to include in the inventory should be based on the importance of these fluxes to the overall carbon budget and not on the perceived ease with which flux estimates can be obtained. [ABSTRACT FROM AUTHOR]