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Dimitrov D.D.,Northern Forestry Center | Grant R.F.,University of Alberta | Lafleur P.M.,Trent University | Humphreys E.R.,Carleton University
Journal of Geophysical Research: Biogeosciences | Year: 2010

The ecosys model was applied to examine the effects of peatland hydrology on soil respiration and ecosystem respiration at Mer Bleue peatland, Ontario, Canada. It was hypothesized that a decrease in near-surface microbial respiration in peat hummocks resulting from water table (WT) drawdown and subsequent desiccation of the uppermost peat would offset an increase of soil respiration at depth with improved aeration (respiration offsetting mechanism). In contrast, shallower water table in hollows would not allow near-surface desiccation to offset increased soil respiration at depth during drying. However, increased hollow soil respiration with WT drawdown would be offset by decreased aboveground moss respiration with near-surface desiccation in hummocks. Model results for microbial respiration were tested against independent laboratory experiments and ecosystem respiration against hourly eddy-covariance measurements of bog CO2 exchange from 2000 to 2004. The respiration offsetting mechanism modeled in hummocks resulted in CO 2 production of 0.85 μmol CO2 m-2 s -1 with both low (67 cm) and intermediate (38 cm) water tables in the summers of 2001 and 2004, and of 0.81 μmol CO2 m-2 s-1 and 0.95 μmol CO2 m-2 s-1 with high (31 cm) and intermediate (41 cm) water tables in the summers of 2000 and 2001. Ecosystem respiration was 2.01 μmol CO2 m-2 s-1 and 2.23 μmol CO2 m-2 s-1, and 2.62 μmol CO2 m-2 s-1 and 2.58 μmol CO2 m-2 s-1, respectively, during these periods. Our results suggest that ecosystem respiration at Mer Bleue varied little with water table, but this behavior may not be typical for other peatlands. Copyright 2010 by the American Geophysical Union.


Bouriaud O.,Northern Forestry Center | Frank D.,Swiss Federal Institute of forest | Bhatti J.S.,Northern Forestry Center
Ecoscience | Year: 2014

The changes in temperature and precipitation regimes predicted for boreal regions are expected to profoundly affect the productivity of trees situated on waterlogged soils, which underlie large areas of boreal forest in Canada. The consequences for productivity of climatic variation likely depend on site ecology and differ between species. To investigate potential site-dependent responses to climate, we compared the growth of jack pine (Pinus banksiana) trees growing within the same climate conditions but along a transect extending from a fen margin to a sandy ridge. On the fen-margin site, black spruce trees (Picea mariana) were also sampled, allowing for a comparison of the sensitivity of both species. Growth variations at interannual and decadal frequency were analyzed from tree-rings. Our study revealed that the response to climate varied substantially between sites, but, surprisingly, trees growing on the fen margin proved to be very sensitive to fluctuations of precipitation at both interannual and decadal time scales. Black spruce trees responded more sensitively to climate variation than jack pine sampled at the same site. Our study also showed a modest response to temperature even in the driest site. For both species, decadal signals show precipitation as a common, strong productivity driver regardless of water table constraints. These results suggest that the predicted climate warming is therefore less of a threat to the productivity of peatland forested zones than fluctuations in the precipitation regime. Changes in precipitation are expected to have much stronger consequences at both interannual and decadal time scales than projected temperature fluctuations.


Andersen R.,Macaulay Institute | Andersen R.,Laval University | Grasset L.,University of Poitiers | Thormann M.N.,Northern Forestry Center | And 2 more authors.
Soil Biology and Biochemistry | Year: 2010

This study examines the recovery of the microbial compartment following active restoration of a North American ombrotrophic peatland extracted for horticultural peat-based substrates and restored by the Sphagnum moss transfer method. We used phospholipid fatty acids (PLFAs) to portrait the microbial community structure and Community Level Physiological Profiles (CLPP) to describe the functional diversity of the microbial communities. Our results indicate that the PLFA profiles were different between the beginning and the end of the growing season, but that it was impossible to distinguish five different vegetation classes found along the disturbance-recovery gradient on the basis of the microbial community structure. The pH, the cover of mosses, Ledum groenlandicum and Eriophorum vaginatum var. spissum were the best environmental predictors for the PLFA composition. The newly formed peat found in aerobic conditions beneath restored Sphagnum carpets had the highest decomposition capacity, whereas the lowest rates were found in the surface samples of non-restored conditions or in the deepest horizons of the natural samples. A large proportion of the variation in the physiological profiles was explained with variables related to the vegetation cover, the physicochemical environment and the microbial structure of the community, which is very promising for future monitoring studies. Overall, this study demonstrates that the recovery of particular plant groups, namely mosses and shrubs in restored peatlands might be the driver of changes occurring in the structure of the microbial communities in restored peatlands. © 2009 Elsevier Ltd. All rights reserved.


Kettridge N.,University of Birmingham | Thompson D.K.,McMaster University | Thompson D.K.,Northern Forestry Center | Waddington J.M.,McMaster University
Journal of Geophysical Research: Biogeosciences | Year: 2012

Wildfire represents the single largest disturbance to the ecohydrological function of northern peatlands. Alterations to peatland thermal behavior as a result of wildfire will modify the carbon balance of these important long-term global carbon stores and regulate post-fire ecosystem recovery. We simulate the 3-D thermal behavior of a peatland that has been disturbed by wildfire to identify how changes in peat temperatures emerge from changes to the surface energy balance and peat thermal properties. Peat temperatures are simulated within two adjacent peatlands, one area having burned 4 years previously, the second which has been wildfire-free for 75 years. We demonstrate that there is only a small alteration to the thermal response in Sphagnum fuscum hummocks that are not severely burnt within the wildfire. In contrast, wildfire produces important changes to the energy balance of Sphagnum hollows. A large reduction in the latent heat flux post-fire increases surface temperatures by up to 30°C during daytime summer conditions. However, temperatures through the peat profile are insensitive to these increases in surface temperature. The low surface moisture content of near-surface peat insulates the profile from these higher temperatures and, at depths below 0.015 m, only small differences are identifiable between burned and unburned hollow temperatures. Nevertheless, we argue that these alterations to near-surface temperatures and evaporation rates likely substantially influence the thermal and hydrological conditions post-wildfire, impacting the peatland recovery. Copyright 2012 by the American Geophysical Union.


Pinzon J.,University of Alberta | Spence J.R.,University of Alberta | Langor D.W.,Northern Forestry Center
Forest Ecology and Management | Year: 2012

Green tree retention has been embraced as an alternative to large scale conventional clear-cutting aimed at managing the boreal forest in a more sustainable way. Ground-dwelling spider assemblages were studied 6. years after the application of variable retention harvesting practices (dispersed to 2%, 10% and 75% retention vs. aggregated retention) in deciduous and coniferous dominated stands as part of the Ecosystem Management Emulating Natural Disturbances (EMEND) project in the mixedwood boreal forest of northwestern Canada. Overall, spider composition was dominated by open-habitat species, especially by the wolf spider Pardosa moesta Banks, in all harvest treatments. However, an important shift in species composition was observed in unharvested controls. Distinctive ground-dwelling spider assemblages were observed in each forest cover-type and these were highly affected by the various harvest treatments, especially in coniferous forests. From the 164 species collected, 37 were indicators for various combinations of forest type, harvesting treatment and retention level. Species richness was affected as harvesting intensity increased; however, greater impact was observed in dispersed retention than in aggregated retention, and in coniferous stands compared to the same treatment in deciduous stands. Dispersed retention, even at 10%, seemed to mitigate adverse effects of harvesting on spider assemblages, but only in deciduous forests; however, important effects on biodiversity were observed in coniferous forests even after 75% retention. Retention of aggregated patches was useful in maintaining forest specialist species after harvesting, but was more effective when applied together with dispersed retention. Responses of spider assemblages to harvesting seemed to be highly correlated with environmental changes. Green tree retention preserves some of the heterogeneity, structural features and environmental conditions required by forest specialist species and thus becomes an effective management practice to maintain forest biodiversity, especially when both aggregated and dispersed retention practices are applied together. However, the effectiveness of these practices varies depending on the forest cover-type prior to harvesting and the amount of post-harvest residual. This suggests that a single prescription is insufficient for maintaining landscape heterogeneity, and that a combination of prescriptions is supported for a more sustainable management of the mixedwood boreal forest. © 2011 Elsevier B.V.


Arevalo C.B.M.,University of Alberta | Bhatti J.S.,Northern Forestry Center | Chang S.X.,University of Alberta | Jassal R.S.,University of British Columbia | Sidders D.,Northern Forestry Center
Journal of Geophysical Research: Biogeosciences | Year: 2010

This study compares soil respiration and its heterotrophic and autotrophic components in four land use types: agriculture, 2 and 9 year old hybrid poplar plantations, grassland, and a native aspen stand in north central Alberta, Canada, over a period of two growing seasons (2006 and 2007). The differences were examined with respect to substrate quality and quantity, fine root biomass, and nutrient availability, in addition to soil temperature and soil water content. Cumulative soil C loss via soil respiration averaged over the two growing seasons was (in decreasing order) 781, 551, 523, 502, and 428 g C m -2 for native aspen stand, 9 year old hybrid poplar plantation, grassland, agriculture and 2 year old hybrid poplar plantation, respectively. We found that ∼75% of soil respiration in the native aspen stand originated from the top 7.5-10 cm litter-fibric-humus layer. Seasonal heterotrophic and autotrophic respiration among the land uses ranged from 97 to 272 and 333 to 560 g C m-2, respectively, contributing up to 35% and 83% of total soil respiration, respectively. The variability in soil respiration across different land uses was explained mainly by site differences in soil temperature (88-94%). Soil respiration followed a pronounced seasonal trend: increasing during the growing season and converging to a minimum in the fall. Soil respiration under different land uses was influenced by (1) ecosystem C stock, (2) temperature sensitivity (Q10) of organic matter present, and (3) organic matter decomposability as indicated by the natural abundance of δ13C. Heterotrophic respiration was influenced by soil temperature, while autotrophic respiration was influenced by fine root biomass and nutrient (NO 3 - and P) availability. These results are useful in estimating potential responses of soil respiration and its components to future land management and climate change. Copyright 2010 by the American Geophysical Union.


Beverly J.L.,Northern Forestry Center | Beverly J.L.,University of Toronto | Bothwell P.,Northern Forestry Center
Natural Hazards | Year: 2011

Evacuations represent an integral aspect of protecting public safety in locations where intense, fast-spreading forest fires co-occur with human populations. Most Canadian fire management agencies have as their primary objective the protection of people and property, and all fire management agencies in Canada recommend evacuations when public safety is in question. This study provides the first national assessment of wildfire-related evacuations in Canada and documents the loss of homes that coincided with evacuation events. The most striking finding is that despite the intensity and abundance of wildfire in Canada, wildfires have displaced a relatively small number of people. Between 1980 and 2007, the median number of evacuees and home losses per year in Canada were 3,590 and 2, respectively. Evacuees' homes survived in 99.3% of cases. Patterns of evacuations and home losses reflected the distributions of forests, wildfire, and people across the Canadian landscape. Most evacuations occurred in boreal areas, which have relatively low population densities but among the highest percent annual area burned in Canada. Evacuations were less common in southern parts of the country, where most Canadians reside, but individual wildfires in these areas had significant impacts. Interactions between wildfire and people in Canada exhibited a unique regional pattern, and within the most densely populated regions of the country they can be considered 'low-probability, high-consequence' events. This Canadian context is fundamentally different from places such as California, where concentrations of fires and people overlap across large areas and therefore calls for a fundamentally different fire management response. © 2011 Her Majesty the Queen in right of Canada.


Hely C.,Aix - Marseille University | Fortin C.M.-J.,University of Toronto | Anderson K.R.,Northern Forestry Center | Bergeron Y.,University of Québec
International Journal of Wildland Fire | Year: 2010

Wildfire simulations were carried out using the Prescribed Fire Analysis System (PFAS) to study the effect of landscape composition on fire sizes in eastern Canadian boreal forests. We used the Lake Duparquet forest as reference, plus 13 forest mosaic scenarios whose compositions reflected lengths of fire cycle. Three fire weather risks based on duff moisture were used. We performed 100 simulations per risk and mosaic, with topography and hydrology set constant for the reference. Results showed that both weather and landscape composition significantly influenced fire sizes. Weather related to fire propagation explained almost 79% of the variance, while landscape composition and weather conditions for ignition explained ∼14 and 2% respectively. In terms of landscape, burned area increased with increasing presence of shade-tolerant species, which are related to long fire cycles. Comparisons among the distributions of cumulated area burned from scenarios plus those from the Société de Protection des Forêts contre le Feu database archives showed that PFAS simulated realistic fire sizes using the 80-100% class of probable fire extent. Future analyses would best be performed on a larger region as the limited size of the study area could not capture fires larger than 11000ha, which represent 3% of fires but 65% of the total area burned at the provincial scale. © IAWF 2010.


Wang Y.,Northern Forestry Center | Anderson K.R.,Northern Forestry Center
International Journal of Wildland Fire | Year: 2010

We used the K-function and kernel estimation methods to evaluate the spatial and temporal patterns of ignition locations of lightning- and human-caused forest fires in Alberta, Canada. Although both of these fire types have spatial patterns of cluster distribution, quantitative measures for evaluating the patterns in the province are lacking. Our results revealed annual differences in the spatial patterns between the two fire types, whereby fires caused by humans tended to be more clustered and had more complex spatial patterns than those caused by lightning. Spatial interactions of cluster and inhibition existed between the two fire types. Human-caused fires in the period 2003-07 were highly concentrated in the southern parts of the province, indicating the existence of an interaction between space and time. Kernel analysis confirmed the observation that in northern Alberta, lightning-caused fires were more likely to occur than human-caused fires; the opposite was true in southern Alberta. This study provided useful spatial information that is not obvious or cannot be inferred from visual examination of raw data. Such quantitative knowledge could lead to the development of fire-response and fire-suppression strategies appropriate to specific regions within the province. © IAWF 2010.


Cullingham C.I.,University of Alberta | Cooke J.E.K.,University of Alberta | Dang S.,University of Alberta | Davis C.S.,University of Alberta | And 2 more authors.
Molecular Ecology | Year: 2011

The current epidemic of the mountain pine beetle (MPB), an indigenous pest of western North American pine, has resulted in significant losses of lodgepole pine. The leading edge has reached Alberta where forest composition shifts from lodgepole to jack pine through a hybrid zone. The susceptibility of jack pine to MPB is a major concern, but there has been no evidence of host-range expansion, in part due to the difficulty in distinguishing the parentals and their hybrids. We tested the utility of a panel of microsatellite loci optimized for both species to classify lodgepole pine, jack pine and their hybrids using simulated data. We were able to accurately classify simulated individuals, and hence applied these markers to identify the ancestry of attacked trees. Here we show for the first time successful MPB attack in natural jack pine stands at the leading edge of the epidemic. This once unsuitable habitat is now a novel environment for MPB to exploit, a potential risk which could be exacerbated by further climate change. The consequences of host-range expansion for the vast boreal ecosystem could be significant. © 2011 Blackwell Publishing Ltd.

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