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Goring S.,Simon Fraser University | Lacourse T.,University of Victoria | Pellatt M.G.,Western and Northern Service Center | Pellatt M.G.,Simon Fraser University | And 2 more authors.
Review of Palaeobotany and Palynology

Differences between pollen assemblages obtained from lacustrine and terrestrial surface sediments may affect the ability to obtain reliable pollen-based climate reconstructions. We test the effect of combining modern pollen samples from multiple depositional environments on various pollen-based climate reconstruction methods using modern pollen samples from British Columbia, Canada and adjacent Washington, Montana, Idaho and Oregon states. This dataset includes samples from a number of depositional environments including soil and lacustrine sediments. Combining lacustrine and terrestrial (soil) samples increases root mean squared error of prediction (RMSEP) for reconstructions of summer growing degree days when weighted-averaging partial-least-squares (WAPLS), weighted-averaging (WA) and the non-metric-multidimensional-scaling/generalized-additive-models (NMDS/GAM) are used but reduces RMSEP for randomForest, the modern analogue technique (MAT) and the Mixed method, although a slight increase occurs for MAT at the highest sample size. Summer precipitation reconstructions using MAT, randomForest and NMDS/GAM suffer from increased RMSEP when both lacustrine and terrestrial samples are used, but WA, WAPLS and the Mixed method show declines in RMSEP.These results indicate that researchers interested in using pollen databases to reconstruct climate variables need to consider the depositional environments of samples within the analytical dataset since pooled datasets can increase model error for some climate variables. However, since the effects of the pooled datasets will vary between climate variables and between pollen-based climate reconstruction methods we do not reject the use of mixed samples altogether. We finish by proposing steps to test whether significant reductions in model error can be obtained by splitting or combining samples from multiple substrates. © 2010 Elsevier B.V. Source

Macdonald L.A.,University of Waterloo | Turner K.W.,Wilfrid Laurier University | Balasubramaniam A.M.,University of Waterloo | Wolfe B.B.,Wilfrid Laurier University | And 3 more authors.
Hydrological Processes

Recent studies using remote sensing analysis of lake-rich thermokarst landscapes have documented evidence of declining lake surface area in response to recent warming. However, images alone cannot identify whether these declines are due to increasing frequency of lake drainage events associated with accelerated thermokarst activity or to increasing evaporation in response to longer ice-free season duration. Here, we explore the potential of combining aerial photograph time series with paleolimnological analyses to track changes in hydrological conditions of a thermokarst lake in the Old Crow Flats (OCF), Canada, and to identify their causes. Images show that the water level in lake OCF 48 declined markedly sometime between 1972 and 2001. In a sediment core from OCF 48, complacent stratigraphic profiles of several physical, geochemical, and biological parameters from ∼1874-1967 indicate hydro-limnological conditions were relatively stable. From ∼1967-1989, declines in organic matter content, organic carbon isotope values, and pigment concentrations are interpreted to reflect an increase in supply of minerogenic sediment, and subsequent decline in aquatic productivity, caused by increased thermo-erosion of shoreline soils. Lake expansion was likely caused by increased summer rainfall, as recorded by increased cellulose-inferred lake-water oxygen isotope compositions. Stratigraphic trends defining the lake expansion phase terminated at ∼1989, which likely marks the year when the lake drained. Above-average precipitation during the previous year probably raised the lake level and promoted further thermo-erosion of the shoreline soils that caused the lake to drain. These are meteorological conditions that have led to other recent lake-drainage events in the OCF. Thus, the decline in lake level, evident in the aerial photograph from 2001, is unlikely to have been caused by evaporation, but rather is a remnant of a drainage event that took place more than a decade earlier. After drainage, the lake began to refill, and most paleolimnological parameters approach levels that are similar to those during the stable phase. These findings indicate that combined use of aerial images and paleolimnological methods offers much promise for identifying the hydrological consequences of recent climatic variations on thermokarst lakes. © 2011 John Wiley & Sons, Ltd. Source

Soverel N.O.,University of British Columbia | Coops N.C.,University of British Columbia | Perrakis D.D.B.,Western and Northern Service Center | Daniels L.D.,University of British Columbia | Gergel S.E.,University of British Columbia
International Journal of Wildland Fire

Wildfire is a complex and critical ecological process that is an integral component of western Canadian terrestrial ecosystems. Therefore, Canadian land management agencies such as Parks Canada require detailed burn severity data for the monitoring and managing of both wildland and prescribed fires. In order to gather this type of information for our study, the acquisition of Landsat imagery was acquired and the differenced Normalised Burn Ratio was computed, a technique that has been shown to be sensitive to field measured burn severity. It is less known if this technique can be transferred and extrapolated over space and time so as to make routine and operational application of the approach feasible. To answer this question, we combined burn severity data from 10 fires across western Canada to test the transferability of an overall model as well as one stratified by land cover and ecozone. Finally, we tested the statistical benefit of incorporating pre- and post-fire data directly into the statistical model using transformations of the remote sensing imagery. Our results indicated that an overall differenced Normalised Burn Ratio derived model successfully estimated burn severity for the majority of fires in the study, which supports its transferability across multiple western Canadian landscapes. © 2011 IAWF. Source

Bastien J.-S.,UniversiteLaval | Fortin D.,UniversiteLaval | Wilmshurst J.F.,Western and Northern Service Center | Fortin M.-E.,UniversiteLaval

Developing tools that help predict animal distribution in the face of environmental change is central to understanding ecosystem function, but it remains a significant ecological challenge. We tested whether a single foraging currency could explain bison (Bison bison) distribution in dissimilar environments: a largely forested environment in Prince Albert National Park (Saskatchewan, Canada) and a prairie environment in Grasslands National Park (Saskatchewan, Canada). We blended extensive behavioral observations, relocations of radio-collared bison, vegetation surveys, and laboratory analyses to spatially link bison distribution in the two parks and expected gains for different nutritional currencies. In Prince Albert National Park, bison were more closely associated with the distribution of plants that maximized their instantaneous energy intake rate (IDE) than their daily intake of digestible energy. This result reflected both bison's intensity of use of individual meadows and their selection of foraging sites within meadows. On this basis, we tested whether IDE could explain the spatial dynamics of bison reintroduced to Grasslands National Park. As predicted, bison distribution in this park best matched spatial patterns of plants offering rapid IDE rather than rapid sodium intake, phosphorus intake, or daily intake of digestible energy. Because the two study areas have very different plant communities, a phenomenological model of resource selection developed in one area could not be used to predict animal distribution in the other. We were able, however, to successfully infer the distribution of bison from their foraging objective. This consistency in foraging currency across ecosystems and populations provides a strong basis for forecasting animal distributions in novel and dynamic environments. © 2011 by the Ecological Society of America. Source

Desellas A.M.,Queens University | Desellas A.M.,Environment Canada | Paterson A.M.,Environment Canada | Sweetman J.N.,Queens University | And 2 more authors.
Journal of Limnology

Zooplankton communities in Boreal Shield lakes of south-central Ontario, Canada, have become increasingly exposed to the effects of multiple anthropogenic stressors, such as declines in calcium (Ca) and total phosphorus (TP) concentrations, shifts in predation regimes, and climate warming. The paleolimnological approach provides an effective means of examining cladoceran zooplankton communities prior to the onset of these major environmental stressors and assessing how the increasing impacts of these stressors have affected zooplankton community composition. We examined the chitinized remains of cladocerans from recent and pre-industrial (pre- ~1850s) sediments in 42 oligotrophic lakes from south-central Ontario and compared these assemblages using ANOSIM and SIMPER. Differences in cladoceran assemblages since pre-industrial times were related to five environmental variables that significantly influence cladoceran community composition in surface sediments. These included measured physical (depth), chemical [Ca, pH, sulphate, dissolved organic carbon (DOC)], and biological (fish community biomass) limnological variables. Two changes were recorded in the cladoceran species assemblages of the study lakes. The first was a significant increase in the ratio of pelagic species compared to littoral species over time in most lakes which we cannot attribute to any measured environmental variable with certainty but it likely represents a multiple stressor effect. The second was changes in relative abundances of daphniid cladocerans in several lakes since pre-industrial times, which we attribute to the interactive effects of several environmental stressors, including: differences in Ca availability within our lakes, resulting in decreased abundances of daphniids over time in lakes with lower Ca levels; long-term increases in DOC concentrations, which may provide refuge for daphniids from visual predators; and long-term declines in TP concentrations which may contribute to the dominance of species that are more efficient grazers, such as daphniids. Overall, this study provides field-based evidence that the modern-day cladoceran communities in south-central Ontario lakes are different than they were prior to human settlement in the region, and therefore these paleolimnological data provide a long-term, historical component to contemporary cladoceran datasets and an extended perspective on how multiple environmental stressors have impacted aquatic organisms from Boreal Shield lakes. Source

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