Vegetation and soil disturbances in bogs traversed by power line corridors in Manitoba

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Magnusson, Borgthor
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Effects of power line construction and vegetation management on bog vegetation and organic matter breakdown, were examined along two right-of-ways (ROWs) extending from 50-56 oN in Manitoba. Vegetation, peat and soil water were sampled and collected from the ROW and adjacent undisturbed forest at sixteen sites. Organic matter decomposition estimates were derived from measurements of seasonal soil respiration rates in the ROW and forest at three sites. Erosion of exposed peat was estimated in the ROW at three sites. Effects of the herbicides picloram and 2,4-D on growth of Sphagnum fuscum were studied at two sites; and in the laboratory the effects of the herbicides on respiration rate (CO2 production) in S.fuscum peat cores were examined. Decorana ordination and cluster anlysis showed similar patterns in the vegetation. Major groupings were formed along moisture and disturbance gradients. Canonical correlation analysis revealed that variation in bare ground, peat humification and soil water chemistry correlated strongly with the vegetation pattern. Six (among them S.fuscum) of the fifty most abundant plant species were significantly reduced in abundance in the ROW compared to the forest, while only, Polytrichum strictum had significantly higher abundance in the ROW than the forest community. Annual decomposition of soil organic matter was estimated to be of the order 350-670 g dwt m-2 over the latitudinal range of the study area. It was not evident that disturbances in the ROW had affected rates of organic matter decomposition. Organic matter losses due to erosion of surface peat in the ROW were very low in comparison to decompositional losses. Applications of picloram on Sphagnum fuscum growing in hummocks were found to permanently destroy most of the shoots of the moss and suppress its regeneration for several years. Cyclic use of picloram in the type of bogs studied is considered to lead to a gradual destruction of the hummock habitat and its associated community. Picloram and 2,4-D applications caused initial stimulation of respiration rates in peat cores, which were minimal within 30 days of applications. The herbicides were not considered to cause long term changes in peat decomposition rates.