Riparian vegetation change in upstream and downstream reaches of three temperate rivers dammed for hydroelectric generation in British Columbia, Canada

River flow regulation by dams for hydroelectric generation has been a common practice worldwide for centuries, with diverse ecological impacts. We studied upstream and downstream reaches of three British Columbia Hydro reservoirs on the Allouette, Coquitlam, and Cheakamus Rivers to determine if riparian plant communities were affected by the dams. We determined cover of all plants in consecutive 1 m2 quadrats along five to six 14 m-long belt transects in each 300 m upstream and downstream sections of these rivers. We encountered 166 plant species in a total of 448 quadrats. Differences in plant communities (abundance, species richness, diversity) amongst rivers were larger than that between the upstream versus downstream of the rivers. This suggests that any difference caused by reservoir management was within the natural range of variation found across the rivers. We found significant reductions in the occurrences of red alder and western red cedar downstream of reservoirs. The lack of regeneration of these two species may be attributable to the reduction in extremes of flow variation and lack of sediment transport due to the reservoirs. Coordinated flow management can help mitigate these downstream impacts.