Tolerance of fen mosses to submergence, and the influence on moss community composition and ecosystem resilience

Question: Flood disturbance in peatlands can create temporary or permanently submerged areas where tolerant species may persist and replace intolerant species over time. Fen moss species and communities occur along a hummock-hollow gradient in natural ecosystems, but their resistance and resilience to different durations of submergence has yet to be tested. We asked what are the short- and long-term effects of submergence duration on four common boreal fen moss species and the implications for ecosystem resilience? Location: Rich fen near Fort McMurray, Alberta, Canada. Methods: To examine the effect of submergence duration on fen moss species and communities, we harvested and submerged monoculture plugs dominated by Hamatocaulis vernicosus, Sphagnum warnstorfii, Tomentypnum nitens and Aulacomnium palustre in the field under rich fen water for 1-8 weeks. After submergence, we planted the plugs in bare peat at the same site to evaluate the short- and long-term responses of each species and changes in moss community composition over time. Results: We found that moss species response to duration of submergence is not strictly related to their occurrence along a hummock-hollow gradient and that tolerant species maintain or restore moss cover. H. vernicosus was most tolerant to submergence of all durations, whereas S. warnstorfii was nearly eliminated by submergence. Over the long term, more tolerant species replaced less tolerant species, increasing diversity and moss community resilience. Overall, moss communities without S. warnstorfii were resilient to 4 weeks of submergence because T. nitens and H. vernicosus maintained dominance or established where the cover of less resilient species was limited. Conclusions: We show that moss species varied in their responses to submergence duration, resulting in shifts in community composition and long-term effects on community resilience with longer durations of submergence. This provides insight into how moss communities provide stability to peatlands in response to disturbance through shifts in community composition that support tolerant dominant species.