Succession of a degraded bog in NE Denmark over 164 years-monitoring one of the earliest restoration experiments

We present the results of a unique study of long-term succession in a former raised bog after intensive peat cutting. As probably one of the first restoration experiments the study site 'Gammelmose' (22 ha) in NE Zealand, Denmark, was in 1844 protected from any further human usage. Since then several surveys of water level, peat re-growth and vegetation change were carried out in 18 permanent plots. The vegetation data from 1861, 1885, 1963, 1981 and 2005 were analysed with DCA and correlated with selected environmental variables. The peat layer increased in thickness by <1 m within the period 1859-2005, and the bog surface became slightly convex; the water level was at 10-20cm belowground in 2005. The vegetation developed from an open wetland with a number of fen species over a phase with locally dominant Phragmites australis to a half-open birch-pine forest with abundant Sphagnum-mosses. The increasing frequency of woody species was reflected by lower Ellenberg indicator values for light and soil moisture. The first DCA axis was correlated with succession time and frequency of woody species, and negatively with the two Ellenberg indicator values. The second DCA axis was also correlated with time and woody species, but negatively with Ellenberg values of soil nutrients and soil reaction. In the period 1861-2005, several fen species with relatively high demands for light and nutrients disappeared (e.g. Peucedanum palustre, Stellaria palustris, Viola palustris), while most bog species continued (e.g. Andromeda polifolia, Vaccinium oxycoccos, V. uliginosum), and new plant species - mainly naturalised from gardens - immigrated (e.g. Spiraea alba var. latifolia, Picea glauca, Prunus padus). In 2005, the vitality and growth of many trees in the bog looked reduced, and some of the taller individuals began to sink into the peat layer. Thus, in future the half-open bog forest may show some natural dynamics allowing survival of bog species in a mosaic of changing microhabitats.