Biodiversity loss caused by subsurface pipe drainage is difficult to restore

Abstract Subsurface pipe drainage was a frequently used way of agriculture intensification. Here, we present a case study of peat meadows that were drained from the mid 1980s to 1990s and were restored by interrupting drainage pipes through clay sealed trenches. This trial was subject of extensive survey of plant, soil fauna and soil chemistry, which was done just before restoration and then repeated 20 years later. The water table was the closest to surface in undrained meadows and much deeper in drained and restored meadows during both times. In the restored meadow, some increase of the water table was observed, but the water table was mostly within 60 cm of the surface. Undrained meadow was much richer in soil organic carbon. Plant communities in both drained and restored plots become closer to those in undrained remnants 20 years after restoration. Community weighted mean for Ellenberger values showed that undrained peat meadow remnants were more oligotrophic than drained and restored sites. Soil fauna communities of undrained remnants and both drained treatments were clearly separated in 1990s and lumped together 20 years later. This was caused by a shift in the communities in both drained treatments but also by degradation of undrained remnants, which shifted towards drained sites. The results show that restoration slightly shifted the communities towards the undrained reference sites, but the shift was not much bigger that those in drained sites and in both cases, do not result in peat formation. Control sites also show some degradation most likely due to eutrophication.