Plant community composition along a peatland margin follows alternate successional pathways after hydrologic disturbance

Hydrological disturbances can alter the structure and function of ecosystems by changing plant species composition over time. Peatlands in the northern hemisphere are particularly sensitive to global change drivers related to soil water availability, such as drought and drainage, because of important ecohydrological feedbacks between species composition and water table position. Here, we examined the plant community structure and environmental drivers of species distributions over two growing seasons along a bog - margin gradient, pre- and post-disturbance by beaver activity. Pond drainage resulted in seasonal average water table depth 8-24 cm lower in the second season. Five plant communities corresponded to changes in water table depth and acidity: bog, poor fen, meadow, mudflat and pond. Plant cover increased in meadow and mudflat communities, decreased in the pond community and did not differ between years in bog and poor fen communities. Changes in species abundance between years showed signs of alternate successional pathways: one that favors Sphagnum moss and bog community expansion and another pathway that favors meadow and mudflat expansion. This study highlights the non-linear successional trajectory of plant communities with changes in water table depth, which has implications for land management goals that aim to conserve the ecological integrity of peatland ecosystems.