Restoration of temperate forestry-drained fens brings back key species and an ecosystem function

Abstract Fen peatlands act as carbon sinks and are hotspots for specialised species, but a large proportion of fens have been drained for agricultural or forestry use. Drainage turns peatlands from carbon sink to carbon source, and negatively affects specialised biodiversity. Although restoration by rewetting can partially improve ecosystem functions, the successful recovery of specialised biota depends on previous land use. Rewetting agriculturally used fens often results in an ecosystem that does not resemble the original fen. The vegetation recovery of rewetted fens used for forestry is more promising, but our knowledge of vegetation development comes from boreal fens. It is unclear whether vegetation can successfully recover after the rewetting of forestry-drained fens in the temperate zone. Our study focused on the recovery of vegetation and peat accumulation in small fens in temperate Europe, located in a large forest complex in Germany, that had been drained for forestry and restored by rewetting over the 38 years prior to the study. We compared the restored sites to degraded and near-natural ones. We recorded vegetation composition and measured peat depth. We demonstrate that peat layers continuously increased with time since restoration, possibly indicating peat accumulation, which is crucial for converting drained fens back into carbon sinks. The vegetation composition of the restored sites became increasingly similar to that of the near-natural sites over time, with the steepest change occurring during the first 10 years after restoration. Nevertheless, even after decades, the vegetation did not reach the quality of near-natural sites. Synthesis and applications: Our results highlight that rewetting forestry-drained temperate fens can lead to partial vegetation recovery and jump-start peat formation.