Effects of Livestock Grazing and Well Construction on Prairie Vegetation Structure Surrounding Shallow Natural Gas Wells
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Short and sparse vegetation near shallow gas wells has generally been attributed to residual effects from well construction, but other mechanisms might also explain these trends. We evaluated effects of distance to shallow gas wells on vegetation and bare ground in mixed-grass prairies in southern Alberta, Canada, from 2010 to 2011. We then tested three hypotheses to explain why we found shorter vegetation and more bare ground near wells, using cattle fecal pat transects from 2012, and our vegetation quadrats. We evaluated whether empirical evidence suggested that observed patterns were driven by (1) higher abundance of crested wheatgrass (Agropyron cristatum) near wells, (2) residual effects of well construction, or (3) attraction of livestock to wells. Crested wheatgrass occurrence was higher near wells, but this did not explain effects of wells on vegetation structure. Correlations between distance to wells and litter depth were the highest near newer wells, providing support for the construction hypothesis. However, effects of distance to wells on other vegetation metrics did not decline as time since well construction increased, suggesting that other mechanisms explained observed edge effects. Cattle abundance was substantially higher near wells, and this effect corresponded with changes in habitat structure. Our results suggest that both residual effects of well construction and cattle behavior may explain effects of shallow gas wells on habitat structure in mixed-grass prairies, and thus, to be effective, mitigation strategies must address both mechanisms.
KeywordsEdge effects Grasslands Habitat structure Livestock grazing Natural gas
We thank three anonymous reviewers and Drs. Efroymson and Collins for their helpful reviews of the manuscript. J. Heese, of Cenovus Energy, provided helpful information on changes in well construction and restoration methods over time. We thank the Eastern Irrigation District and Cenovus Energy for allowing us access to their rangelands and lease sites for our research. Numerous research assistants and graduate students contributed to data collection. This research was supported by Cenovus Energy, Natural Sciences and Engineering Research Council, Canadian Foundation for Innovation, the Manitoba Research and Innovations Fund, and the Clayton H. Riddell Faculty of Environment, Earth and Resources Endowment Fund.
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