Small-scale fen restoration brings back key species and ecosystem functions

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, which turns them 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 that had been drained for forestry and restored by rewetting over the 38 years prior to the study. 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. Our results highlight that rewetting forestry-drained fens can restore ecosystem services and lead to partial vegetation recovery in both the boreal and temperate zones.