Mechanisms involved in the re-establishment of Sphagnum-dominated vegetation in rewetted bog remnants

Restoration of peat bog vegetation in highly degraded peatlands is generally attempted by improving the hydrology of these areas. The present paper discusses and explains various restoration strategies relating to peat quality, water chemistry and hydrology. In some cases, (shallow) inundation of bog remnants leads to a rapid redevelopment of (floating) Sphagnum vegetation, usually when poorly humified Sphagnum peat is still present. After inundation, the peat either swells up to the newly created water table or becomes buoyant, in both cases creating a favorable substrate for Sphagnum mosses. Bulk density and methane production rate play an important role in the buoyancy of floating peat, methane providing buoyancy to the substrates. The presence of (slightly) calcareous groundwater in the peat base may enhance the development of floating rafts by stimulating decomposition processes. Alternatively, the growth of submerged Sphagnum species can also lead to the development of floating rafts. This depends on the penetration of light into the water layer and the availability of carbon dioxide in the water layer. Many bog remnants, however, only have strongly humified peat, which does not favor the redevelopment of Sphagnum carpets after deep inundation. On the other hand, most peat moss species appear to do very well on surface soaked black peat, which is why shallow inundation (< 0.3 m) is to be preferred in such cases. Compartmentalization of the terrain will probably be necessary to ensure a more or less constant water table. An important prerequisite for the successful restoration of bog remnants is the development of a hydrologically self-regulating acrotelm. Key species involved in this development are Sphagnum magellanicum, Sphagnum papillosum and Sphagnum rubellum. These typical hummock and lawn species are usually very slow colonizers compared to hollow species such as Sphagnum cuspidatum and Sphagnum fallax. Introduction of key species in carpets dominated by hollow species or on bare substrates appears to be very successful, indicating that the main constraint is colonization.