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Thesis Examination - MSc Student Johanna RM Robson

Wed. Aug. 8 10:00 AM - Wed. Aug. 8 12:00 PM
Location: 1RC028 (Graduate Studies Boardroom, 1st Floor of Richardson College)

Growth Response of Peatland Black Spruce Trees to Hydrological Variability in Southern Boreal Peatlands, Central Canada

Peatland ecosystems are valuable for their role in carbon sequestration, hydrological regulation and biodiversity. One third of global peatlands are located in Canada. These peatlands are dominated by black spruce [Picea mariana (Mill.) B.S.P.], an important species in Canadian dendrochronology research. Peatlands are also a valuable source of preserved subfossil specimens used in dendrochronological reconstructions. However, in North America, peatland tree-ring studies have been mainly restricted to northern peatlands with evidence of permafrost. The objective of this study was to assess the radial growth and hydroclimate association of peatland black spruce trees growing in three distinct habitats within the Caribou Bog Cluster of southeastern Manitoba. The peatland black spruce growth was also compared to upland stands of black spruce, jack pine and white spruce in the study area. The study area is located in southeast Manitoba at the southern limits of the boreal forest and of peatland development. Tree-ring chronologies were developed following standard dendrochronological procedures. Regime-shift analyses and DendroClim 2002 were used to examine radial growth patterns and hydroclimate – radial growth correlations.

The results indicated that peatland black spruce habitats were characterized by common low frequency growth fluctuations associated with hydrological variability. Growth suppressions in the peatland chronologies were associated with local streamflow peaks as well as regional flooding events for the Red River in southern Manitoba. The peatland habitats with the highest water tables were generally more sensitive to hydrological variability and had strong short-term lagged negative correlation with seasonal streamflow. In comparison, peatland habitats with lower water tables had stronger negative lagged correlations with winter temperature and precipitation. In contrast to previous dendroclimatic studies of black spruce conducted on well-drained upland soils habitats, the radial growth of peatland black spruce trees were not negatively associated with summer moisture deficits or high temperatures.

The results of this study suggested that peatland habitats with high water tables may be valuable for reconstructing historical hydroclimate variability in the southern boreal forest. Based on historical climate changes and evidence that the distribution extent of peatlands has persisted for centuries, peatlands in the southern boreal may be resilient to temperature increases predicted by climate change. Reconstructions of historical hydrological variability in peatlands provided by tree rings is essential for providing baseline data used in successful peatland restoration following peat harvesting.