Browsing by Subject "EASTERN CANADA"

Sort by: Order: Results:

Now showing items 1-3 of 3
  • Dalton, April S.; Finkelstein, Sarah A.; Barnett, Peter J.; Valiranta, Minna; Forman, Steven L. (2018)
    Stratigraphic records from formerly glaciated regions are critical for detailed study of the timing, onset and dynamics of past ice sheets and the palaeoecology of previous ice-free intervals. We examined three stratigraphic sections from an 18-km stretch of the Albany River, Hudson Bay Lowlands, Canada, located at the geographic center for many Late Pleistocene ice sheets. Till characterization and correlation suggest that at least three glacial advances from shifting ice centers within the Labrador sector of the Laurentide Ice Sheet were preserved in these stratigraphic records. Non-glacial units (fluvial, organic-bearing sediments) were constrained via optically stimulated luminescence to two possible periods at ca. 73,000 to 68,000 yr BP and ca. 60,000 yr BP. Boreal and peatland taxa (Picea, Pinus, Poaceae, Betula, Cyperaceae, Sphagnum) dominated the pollen record at each site, whereas plant macrofossils analyzed at one site confirm the local presence of conifer trees (bark, needles, seed wings), bryophytes (largely Scotpidium spp), herbaceous plants (Caryophyllaceae, Carex, Poaceae), and an aquatic setting (e.g. Potamogeton, ephippia of Daphnia spp). Pollen-derived average summer temperature reconstructions suggested that local temperatures at the Albany sites were between 12 and 15 degrees C, which is similar to present-day estimates for the region (14.2 degrees C). Reconstructed annual precipitation estimates were 580-640 mm, which is similar to slightly higher than present-day estimates (564 mm). Non-glacial intervals at the Albany sites likely represent abandoned fluvial environments that supported water-logged peatland biota. Results from this research contribute toward ongoing efforts to constrain ice sheet dynamics over North America during the last glacial cycle (e.g. 71,000-14,000 yr BP) and provide insight into the complex Late Pleistocene palaeoclimate record at the innermost area of the glaciated region.
  • Amesbury, Matthew J.; Booth, Robert K.; Roland, Thomas P.; Bunbury, Joan; Clifford, Michael J.; Charman, Dan J.; Elliot, Suzanne; Finkelstein, Sarah; Garneau, Michelle; Hughes, Paul D. M.; Lamarre, Alexandre; Loisel, Julie; Mackay, Helen; Magnan, Gabriel; Markel, Erin R.; Mitchell, Edward A. D.; Payne, Richard J.; Pelletier, Nicolas; Roe, Helen; Sullivan, Maura E.; Swindles, Graeme T.; Talbot, Julie; van Bellen, Simon; Warner, Barry G. (2018)
    Fossil testate amoeba assemblages have been used to reconstruct peatland palaeohydrology for more than two decades. While transfer function training sets are typically of local-to regional-scale in extent, combining those data to cover broad ecohydrological gradients, from the regional-to continental- and hemispheric-scales, is useful to assess if ecological optima of species vary geographically and therefore may have also varied over time. Continental-scale transfer functions can also maximise modern analogue quality without losing reconstructive skill, providing the opportunity to contextualise understanding of purely statistical outputs with greater insight into the biogeography of organisms. Here, we compiled, at moderate taxonomic resolution, a dataset of nearly 2000 modern surface peatland testate amoeba samples from 137 peatlands throughout North America. We developed transfer functions using four model types, tested them statistically and applied them to independent palaeoenvironmental data. By subdividing the dataset into eco-regions, we examined biogeographical patterns of hydrological optima and species distribution across North America. We combined our new dataset with data from Europe to create a combined transfer function. The performance of our North-American transfer function was equivalent to published models and reconstructions were comparable to those developed using regional training sets. The new model can therefore be used as an effective tool to reconstruct peatland palaeohydrology throughout the North American continent. Some eco-regions exhibited lower taxonomic diversity and some key indicator taxa had restricted ranges. However, these patterns occurred against a background of general cosmopolitanism, at the moderate taxonomic resolution used. Likely biogeographical patterns at higher taxonomic resolution therefore do not affect transfer function performance. Output from the combined North American and European model suggested that any geographical limit of scale beyond which further compilation of peatland testate amoeba data would not be valid has not yet been reached, therefore advocating the potential for a Holarctic synthesis of peatland testate amoeba data. Extending data synthesis to the tropics and the Southern Hemisphere would be more challenging due to higher regional endemism in those areas. (C) 2018 The Authors. Published by Elsevier Ltd.
  • Kuuluvainen, Timo; Gauthier, Sylvie (2018)
    The circumboreal forest encompasses diverse landscape structures, dynamics and forest age distributions determined by their physical setting, and historical and current disturbance regimes. However, due to intensifying forest utilisation, and in certain areas due to increasing natural disturbances, boreal forest age-class structures have changed rapidly, so that the proportion of old forest has substantially declined, while that of young post-harvest and post-natural-disturbance forest proportions have increased. In the future, with a warming climate in certain boreal regions, this trend may further be enhanced due to an increase in natural disturbances and large-scale use of forest biomass to replace fossil-based fuels and products. The major drivers of change of forest age class distributions and structures include the use of clearcut short-rotation harvesting, more frequent and severe natural disturbances due to climate warming in certain regions. The decline in old forest area, and increase in managed young forest lacking natural post-disturbance structural legacies, represent a major transformation in the ecological conditions of the boreal forest beyond historical limits of variability. This may introduce a threat to biodiversity, ecosystem resilience and long-term adaptive capacity of the forest ecosystem. To safeguard boreal forest biodiversity and ecosystem functioning, and to maintain the multiple services provided to societies by this forest biome, it is pivotal to maintain an adequate share and the ecological qualities of young post-disturbance stages, along with mature forest stages with old-growth characteristics. This requires management for natural post-disturbance legacy structures, and innovative use of diverse uneven-aged and continuous cover management approaches to maintain critical late-successional forest structures in landscapes.