A forest health study of bur oak (Quercus macrocarpa Michx.) and trembling aspen (Populus tremuloides Michx.) stands near a coal-fired generating station, southeastern Manitoba

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Boone, Rachel
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A forest health assessment was performed in stands dominated by bur oak and trembling aspen to study the potential effects of airborne emissions from a 132 MW coal-fired generating station. Forty-two stands were sampled within a 16-km radius of the station for both foliar symptoms and trace element toxicology, and a subset of these were sampled using dendrochronological methods. The concentrations of trace elements in the leaf litter were not spatially congruent with airborne emission deposition models, nor were they at phytotoxic levels, but were related to soil parameters including organic matter and texture. No patterns were found in forest health along directional or distance gradients from the generating station. Trembling aspen stands demonstrated little decline in general, but three of the 19 bur oak plots, all located on thin sandy soils developed on calcareous till, demonstrated branch dieback. In addition to poor soil conditions, two of these sites also had high water tables resulting from the construction of an adjacent road, and exhibited tree mortality. One of these declining bur oak sites was examined with dendrochronological techniques, and displayed marked radial growth decline beginning in 1974, with very suppressed growth after 1977, the year the road was built. None of the other bur oak or trembling aspen stands showed distinct radial decline, and displayed similar radial growth patterns regardless of distance from or direction relative to the generating station. The radial growth of both species was significantly affected by climatic factors. The bur oak decline does not appear to be related to emissions from the station, but is suspected to be a result of poor site status, with urban development as a confounding factor.