Harnessing spontaneous colonization processes for raised-bog restoration: Case studies from the OptiMuM project

Raised bogs in Northern Germany face severe threats from drainage and land use, with more than half having been converted to grasslands and contributing significantly to greenhouse gas emissions. Restoring these ecosystems is crucial for achieving climate goals, such as those set by the Paris Agreement. While bog restoration following peat extraction is well-studied, efforts to restore nutrient-enriched agricultural areas into low-maintenance, self-regulating bog ecosystems are still in their infancy.

As a first step in raised bog restoration projects, topsoil is removed to prepare water-retaining polders. Due to previous agricultural use that did not involve peat extraction, substantial layers of weakly decomposed peat often remain intact. Their water-holding capacity can effectively buffer water table fluctuations, favoring peat moss (Sphagnum) establishment after rewetting. Meanwhile, nutrient legacies from agricultural use and competition from grassland and herb species may prevent the rapid re-establishment of peat mosses.

We found that when restoration areas are located near peat moss refugia, rapid and spontaneous colonization of polders with Sphagna can occur within two years of restoration, while other polders remain free of Sphagnum. This variability presents both opportunities, such as allowing rapid natural and low-effort restoration, and challenges, particularly in planning additional restoration measures (e.g. active introduction of bog species) to account for less favorable initial conditions within a site. In the OptiMuM project, we aim to understand these initial conditions better and focus on developing the best approaches for restoring raised bog habitats on former drained bog grasslands. We investigated the site-specific biotic and abiotic factors that influence spontaneous Sphagnum propagation in former grasslands and aim to identify optimal conditions for moss establishment. Additionally, we examine the emerging composition of Sphagna, their ecological value for raised-bog restoration, and the long-term benefits of these emerging ecosystems.