Sphagnum moss layer growth after restoration of forestry-drained peatlands in Finland

Abstract

Restoration of forestry-drained peatlands aims to restore near-natural hydrology and peat-forming vegetation. Particularly, Sphagnum mosses are important for carbon (C) sequestration through peat accumulation. We investigated the new Sphagnum moss layer in 18 restored peatlands circa 10 years after restoration. The sites were monitored for vegetation, water level, and water chemistry. The post-restoration moss layer had grown on average to 14.9 ± 5.2 cm in thickness, measured from peat cores. An independent method using rooting depths of small pines (Pinus sylvestris) indicated a 15.4 ± 5.4 cm average thickness of the newly formed moss layer. The average dry mass of the post-restoration moss layer was 2882 ± 1318 g/m2. Apparent accumulation rates in the moss layer were 132.5 ± 59.8 g m−2 yr−1 for C and 2.36 ± 0.91 g m−2 yr−1 for nitrogen (N). Growth rates were significantly connected to mire type, latitude, and water quality. Thick moss cover developed well under relatively wet baseline conditions and with water level rise near the pre-restoration peat surface. Moss growth was generally greater in open “oligotrophic” peatlands than in forested or “mesotrophic” sites. N concentration, pH, and electric conductivity of pore water correlated negatively with growth, while phosphorus showed no significant correlations. Our results indicate that a thick Sphagnum moss layer forms rapidly during the first 10 years after successful restoration, with C sequestration rates commonly exceeding those of pristine bogs. Restoration of south-boreal acidic, nutrient-poor peatlands where forest drainage has been unsuccessful appears most promising regarding C sequestration by peat mosses.