Restoration of Mire Ecosystems in Finland
The goal of mire habitat restoration is to return drained mires to their natural state. The first stage is to attempt to restore the natural hydrological regime of a mire, to ensure that the dried out peat can gradually reabsorb moisture. Woodland plants will then gradually give way to mire species, which can regain dominance over mire within just a few years. When the water level remains high, mire vegetation in restored mire habitats will begin to form fresh peat again, just as it does in natural mires.
Attempts are also made to restore original mire landscapes. With the reestablishment of mire vegetation and landscapes, other mire species also gradually return to their former haunts.
But mire habitat restoration work can take decades. There is a particularly urgent need for restoration work in southern Finland, where three-quarters of all mires have been drained.
In restored mire habitats ditches are blocked, and trees may also be felled to reduce the loss of moisture through transpiration, at the same time reproducing the original open mire landscape.
- Boreal Peatland LIFE – a large project to restore over 4,000 hectares of mires (www.metsa.fi/borealpeatlandlife)
Mire Restoration Measures
Mire habitat restoration work triggers the gradual return of drained mire to its natural state.
The mire must become more permanently waterlogged again. This reversion back to the mire's original hydrological regime is a basic precondition for restoration to progress. Raising water levels is best achieved by completely filling in ditches, but ditches can alternatively be dammed.
It is also often necessary to remove trees, since trees lose a lot of moisture through transpiration. The trees felled are those growing on drained mires that would naturally be open or only sparsely wooded. Following such measures mires soon recover their natural mosaic-like patchwork of varying habitats.
Trees are left to grow on spruce mires that would naturally be fairly densely wooded. Restored spruce mires can provide an ideal setting for species that thrive in habitats with moist microclimates and plenty of decaying wood, since the rising water levels induce decay in some of the trees.
Threatened Mire Species
The vegetation found on natural mires is largely determined by the presence or absence of nutrients, and the hydrological regime. Other ecological factors relate to the presence of spruce trees, pine trees, alkaline fens, springs, or flooded grasslands. Under different combinations of these factors, countless distinct types of mire habitat can form - in Finland alone over 100 distinguishable mire types have been described, each with their own characteristic range of species.
About a quarter of all Finland's native plant species are associated with mire habitats, while 80 of the country's approximately 235 breeding bird species are dependent on the continued existence of mires during at least some stage of their life cycle. The rare Frigga's fritillary (Clossiana frigga) is typically found in pine mires, but has disappeared from much of its former range in southern Finland, probably due to changes in local microclimates induced by drainage.
Fertile, nutrient-rich mires have inevitably been most intensively drained, and indeed the characteristic species of such habitats have declined most markedly. About two-thirds of the mire species under threat are characteristic of nutrient-rich fens and spruce mires. Widespread drainage has also made it harder to find more familiar mire species such as cranberries and cloudberries. Nowadays new drainage schemes are very rare, but old ditches are still cleared out periodically.