Does prolonged flooding prevent or enhance regeneration and growth of Sphagnum?

Abstract

Site preparation for restoration of peat-mined bogs in eastern Canada frequently involves the construction of bunds or shallow basins to enhance peat moisture content. As a consequence, Sphagnum reintroduced within restored areas may be subjected to extended periods of flooding, particularly following snow melt or heavy rainfall. This paper examines two aspects of the effect of flooding on growth and development of Sphagnum: (1) the production of innovations (growth buds and shoots) and capitula from plant fragments (six species) under continuous, intermittent or non-flooding conditions, and (2) the growth response of whole plants (10 species) under long-term continuous shallow flooding. The development response of Sphagnum fragments to short-term continuous (8–10 cm), intermittent (−1 to +1 cm) or non-flooding conditions (−3 to 0 cm), was investigated in growth chambers. Environmental parameters were selected to investigate the possible differential effects of early spring flooding (10:7 °C, day:night), or inundation following heavy rainfall events later in the season (20–25:20 °C, day:night). Both temperature regimes yielded similar results. After 1 month of flooding the number of innovations was generally similar to that for non-flooded controls. However, after a further 3 months, fragments that had been flooded for 1 month (either continuously or intermittently) produced more capitula than non-flooded fragments. Although S. fuscum, a hummock-forming species, showed delayed formation of innovations, flooding still increased final capitula production. The growth response of whole Sphagnum plants to long-term continuous flooding in the field (+1 cm), revealed that most species grew well, but that several becoming etiolated. These modifications may result in plants more prone to desiccation during drier events than individual with a regular growth form. It is concluded that limited periods of shallow flooding could enhance Sphagnum development in restored areas. Care must be exercised though, as deep or extensive inundation may result in excessive plant etiolation or cause severe physical disturbances to the restorated areas.