Analyzing the Impacts of Road Construction on the Successional Trajectory of a Poor Fen in Northern Alberta.

English Abstract:

Roads that bisect wetlands can alter their hydrologic connectivity on a local or landscape scale. These impacts were studied in a poor fen located 45 km south of Fort McMurray, Alberta, where a raised road was built across the northern fringe of the fen in 1977. Examination of the fen’s response to this impoundment provided insight into post-disturbance vegetation succession patterns and peatland development. The objectives of this study are to quantify the impacts of the road on fen vegetation composition and microtopography, and to predict its successional trajectory based on current vegetation and hydrology. To quantify the impact of the fen, vegetation cover along with several abiotic variables were measured in 281 1 m² plots. In sixteen 50 m² transects, recent moss growth was calculated by measuring the depth to the root crown of black spruce trees, as the root crown’s position represents the original ground level at time of germination. Density and age of saplings were also measured in these transects. Analysis of vegetation reveals dominance of non-hummock forming species (such as Carex aquatilis) closest to the culvert (located in the NW corner). The average depth of recent moss growth was greater immediately up-gradient of the road (36.2 cm) compared with undisturbed areas (19.7 cm). There were no saplings near the culvert, very few within 220 m up-gradient of the road (12% of total trees), and many saplings in the transects furthest from the road (57%). These data suggests that periodic blockage of the culvert leads to flooding in the immediate area that encourages non-hummock forming species of sedge and moss, making an unfavourable environment for black spruce germination. This cycle of hydrologic disturbance may be preventing some areas of the fen from regaining the original vegetation structure, with implications for the system’s development.