An interesting and well conducted study on restoration of managed pine fens in Finland has recently been published in Applied vegetation science by A.M Laine et al. In general the drainage operations done for forestry in Finland were more systematic and more effective than they were in Sweden as one can see from the graph below.
The common method in Sweden for blocking drainage ditches is a wooden dam, which may or may not be reinforced with a plug of peat and/or mineral soil. In Finland this is also done, but another approach is also used. They simply fill up the ditch, and it can be combined with a buried wooden dam that extends into the side of the ditch and redirects water into the peatland.
The finish study is a 4 year vegetation monitoring study, with one monitoring conducted prior to the restoration in 2006, and the remaining monitorings conducted in 2007-2009. Water level change was also measured.
Their results show, as have many previous studies, that the hydrological restoration occurs quickly. The only species group that responded positive to the restoration was Carex species. Surprisingly Sphagnum species decreased after restoration, and the authors speculate that it may be so that the excavators used damaged the Sphagnum cover, and that it has not yet recovered. Alternatively it may be that the increase in water level has had a negative effect on Sphagnum fuscum and Sphagnum russowi.
It should be said that 3 years after the restoration is not a very long time, and as a German restoration ecologist I know said ”Have patience. The results after 4 year can be quite boring, but the vegetation continues to develop far longer than the time period of a PhD study. It would be interesting to see how this develops in the longer term.
Laine, A., Leppälä, M., Tarvainen, O., Päätalo, M., Seppänen, R., & Tolvanen, A. (2011). Restoration of managed pine fens: effect on hydrology and vegetation Applied Vegetation Science DOI: 10.1111/j.1654-109X.2011.01123.x