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Edmonton, Canada

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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