The study of the seed and spore banks of the sites to be restored showed that their role in regeneration of peatland vegetation was minute. Seed germination from the seed bank was relatively poor in these study sites (Paper III). Seeds of V. myrtillus andV.
uliginosum germinated relatively well, but V. uliginosum and especially E. vaginatum and E. nigrum germinated vigorously from propagules. Vegetative growth started as soon as the samples were placed in the greenhouse, which seems to be the main reproduction strategy in mire ecosystems, as found also by Van der Valk and Davis (1978), who suggested that a more appropriate term for wetland seed banks would be
“propagule banks”. No conifers germinated in this study, although the fen site is surrounded by a pine-spruce stand. The abundant C. vulgaris at the bog site did not germinate from seeds. The low pH of the substrate and the simultaneous occurrence of Cladonia species in the bog surface have been found to reduce germination of Calluna (Helsper and Klerken 1984, Hobbs 1985).
Fen site
The seed banks, however, have been found to play an important role in the regeneration of plant communities in other wetlands, such as marshes (van der Valk and Davis 1978, Smith and Kadleg 1985, ter Heerdt and Drost 1994), shorelines and flooding areas (Nicholson and Keddy 1983, Schneider and Sharitz 1986, McDonald 1993, Jutila 1994).
The tree stand clear-cut, ditch filling, and the constructed feeder ditch caused an immediate change in WT at the beginning of restoration. Because of strongly decreased evapotranspiration at the fen site, the WT fluctuation decreased, and the mean WT remained to a level typical of pristine mires (Lindholm and Markkula 1984, Reinikainen et al. 1984).
Smaller changes in WT occurred at the bog site because it lacked an evaporative tree stand at the prerestoration stage. Damming the ditches at the bog site elevated the WT to a level of a natural bog. The WT changes in ombrotrophic mires are more sensitive to the amount of precipitation (Lindholm and Markkula 1984, Reinikainen et al.
1984).
Vegetation changes were greater at the fen site, where tree removal changed light conditions and the ecohydrological shift was larger. After clear-cutting, the increased light and moisture conditions favored germination of vegetative propagules, especially of E. vaginatum (Paper III). Being efficient in using the increased nutrients (Komulainen et al. 1999), Eriophorum started to grow vigorously. Because Eriophorum is an opportunistic pioneer species, it can rapidly take over the habitat created by restoration of different kinds of peatlands (Grosvernier et al. 1995, Pfadenhauer and Klötzli 1996, Robert et al. 1999, Tuittila et al. 2000). The Eriophorum stage may, however, be a transitional stage towards Carex- and Sphagnum-dominated mire vegetation (Grosvernier et al. 1995, Tuittila et al. 2000). In 1997 true fen species, such as Carex rostrata, Calla palustris, and Potentilla palustris, as well as several species of Sphagna were already present at the fen site. Due to clear-cutting at the restoration sites, the increased light conditions increased vegetation growth in the area nearby (Paper V). Moore and Bellamy (1974) found also that land use changes affect the areas nearby as well, not only the area treated.
At the bog site, dry lichen-covered surface was overtaken by moist Sphagna vegetation and the growth of E. nigrum in hummocks increased considerably, because it was released from epiphytic lichens. Although the Sphagnum cover of lawns and hollows already increased during the first three years, a major change can only be expected after several years (Heikkilä and Lindholm 1994).
Raised WT caused changes in element concentrations in the surface peat. The surrounding watershed, including an esker, served as the main source of mineral nutrients at the fen site. The strongly decreased K concentration may be due to leaching from peat (Damman 1986, 1990, 1995), or it may have been used by the vigorously growing Eriophorum (Malmer 1958, Damman 1986). Restoration-driven changes in element concentrations occurred mostly in the upper 20 cm of peat (Paper V). Because of the low concentrations of mineral elements in the ombrotrophic peat and in precipitation (Mörnsjö 1968, Damman 1986, 1990) the postrestoration changes
in the surface peat nutrient regime of the bog remained small and the change in ecohydrology was less marked than at the fen site.
The abundance and distribution of testacean amoebas, which have been used as ecological indicators (Tolonen 1966, 1986), changed during the restoration years. At the fen site, Nebela militaris almost disappeared during the restoration and was replaced by Cryptodifflugia oviformis. C. oviformis, however, decreased at the surface peat of the bog. This may suggest that conditions in the surface layer at the two sites changed in different ways, because of differences in vegetation cover and the quality and quantity of input water. Increased moisture content at the bog surface deteriorated the living conditions for Amphitrema flavum, which decreased in numbers during restoration, whereas Amphitrema wrightianum and different species of Hyalosphenia benefited from the increased moisture content.
Conclusions
The two studied peatland types - minerotrophic and ombrotrophic - had some similarities during their development. The main trend in the development of both peatlands was from higher to lower nutrient levels. Large-scale climatic changes had an influence on both mires, causing similar types of changes in the chemostratigraphy.
However, the development is strongly influenced by the source of water and changes in the catchment area as well as in quality and quantity of precipitation. The accumulation rates are species-specific and dependent also on decomposition rates.
Drainage changed the ecosystems in both mires, although more for the fen than for the bog. The fen site developed a functional forested site, with two drained, forested mire site types, whereas the bog remained economically unproductive. However, renovation of ditches in the fen site would have been necessary periodically.
When restored, the peatland vegetation regenerated mostly vegetatively, but also from modern seeds and spores which spread into the restored areas from the surroundings.
The potential of seed and spore banks to regenerate the peatland vegetation was rather poor, but the initiation occurred from propagules. Peatland vegetation in both mires spread relatively fast. This means successful restoration. Forest shrubs declined at the fen site and E. vaginatum became dominant. At the bog site, the dense lichen cover almost disappeared and Sphagna increased in size and abundance. The water table level remained high and the peatland ecosystems of the fen and the bog became self-sustainable.
Acknowledgements
This work was carried out at the Department of Forest Ecology, Division of Peatland Ecology and Forestry, University of Helsinki. I am grateful to my supervisor Harri Vasander and to Docent Jukka Laine for introducing me to this field of reseach.
Without them this work would not have started. I want to thank warmly Harri Vasander and Raija Laiho for their encouragement, comments and valuable suggestions on the manuscripts and the thesis. I want to thank Aki Pitkänen with whom I had enjoyable paleoecological discussions. Special thanks also to Markus Holopainen with whom I discovered the interesting field of aerial photography. Silja Aho always
offered her friendly help in the laboratory. I greatly acknowledge the head of the Division, Prof. Juhani Päivänen, for providing me with working facilities. Docents Tapio Lindholm and Heikki Seppä have done a great and laborious job with the pre-examination of my thesis. Many thanks to Michelle de Chantal who revised the English language. My warm thanks go to my friends Leila, Pasi, Paula, Seppo, Timo, Tuula among others for their support during this long process.
This work was financed by the Graduate School of Forest Ecology, the Jenny and Antti Wihuri Foundation, the Finnish Cultural Foundation and the Niemi Foundation. I am grateful to these institutions for making this study financially possible.
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