Restoration of formerly afforested blanket bog: Estimating time for vegetation recovery

Peatland restoration aims to restore hydrology and peat-forming vegetation, supporting other ecosystem functions. However, the time required for complete vegetation recovery is generally unknown. Here, we investigate this in an experimentally restored, formerly afforested blanket bog in northern Scotland, which was plowed, fertilized, and planted with non-native conifers in the mid-1980s. Plowing created three "microforms": Ridges, Original surface, and Furrows. Restoration management took place in two stages: trees were felled and drains blocked in 1998 (Standard treatment); then parts of the area were further rewetted with additional drain-blocking in 2015/2016 (Enhanced treatment). We recorded plant species composition in permanent quadrats 0, 5, 13, and 24 years after the start of restoration. Here we use an ordination-regression-based approach (ORBA) to predict time to plant species compositional recovery compared with a reference (comparable nearby intact blanket bog). For the first 13 years, plant species composition diverged from the reference, then later started to converge. If the current speed and direction of vegetation change were maintained, predicted time to recovery varies between 50-100 years and 120-285 years applying a relaxed or strict criterion for restoration success, respectively. Seven growing seasons after Enhanced treatment, recovery speed increased only for the driest microform, Ridge. Surprisingly, this microform was not predicted to take longer to recover than other microforms under either treatment. On the landscape scale, sloping areas were harder to restore than flatter areas, having longer predicted times to recovery. Complete vegetation restoration may take a long time because of legacies from the afforestation (e.g., increased nutrient availability) and the time taken to fully restore surface morphology and water table. On the other hand, other research has already demonstrated that the site is currently acting as a net carbon sink, despite the incomplete vegetation recovery. We argue that functions may be restored without full recovery of species composition. However, approaching the full suite of species may be desirable to support long-term resilience. Successful peatland restoration needs a strong science-practice partnership, where learning gained from monitoring both damaged and comparable intact peatlands can be used to adapt management interventions.