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Fig. 1.Paludification degree:
green - below 15 %, yellow - 15-50 %, blue - over 50 %
In Karelia, mire ecosystems are, alongside with forests, the predominant type of natural complexes. Open mires cover about 1/4 of the region's territory. Various types of paludified forest should also be added (forested areas with a peat deposit). Thus, the combined proportion of paludified land is nearly 40%. In the Suojärvi District however, the degree of paludification varies notably in different types of landscapes - from less than 15 to over 50 %, including both open mires and forests at different stages of paludification (fig. 1, 2, 3) (Volkov et al., 1993, 1995; Gromtsev 1993, 2000).
According to Kuznetsov & Tokarev (2000) "...Development of mires commenced immediately upon glacial retreat (c. 9000 yrs. BP) and still continues. Mires either filled the basins of small lakes or formed through paludification of forests. In the Suojärvi District, about 340,000 ha is under mires (with a peat deposit thicker than 30 cm), and another 107,000 ha is covered by paludified forest. There prevail poor mesotrophic and ombrotrophic sphagnum mires forming complex systems which comprise also numerous lakes and mineral soil areas. Plentiful depressions between hills and ridges, low surface grade, shallow bedding of groundwater have facilitated the high degree of paludification in the district - 30-40 %, and in lacustrine plain areas - 50-60 %".
Fig. 2.A typical open lakeshore bog
The authors write that "...depending on the mineral nutrition, mires can be oligotrophic (bogs), which are fully rain-fed, as well as transitional mires and fens, which require mineral groundwater recharge to develop. Bogs are widespread in Karelia. In the Suojärvi District they account for 60% of the total area under mires, and are represented by two types with a fairly high diversity of sphagnum and woody-sphagnum communities. Bedrock and Quaternary deposits in the district are acidic and nutrient-poor, wherefore the groundwater feeding mires is very little mineralized. As the result, there exist quite a few transitional mires, both open and treed, with a wide range of communities. According to the mire zoning of Karelia (Yelina et al., 1984), Suojärvi District territory belongs to the mire district of mesotrophic, herb-sphagnum and oligotrophic, ridge-hollow, sphagnum mires of the West Karelian upland. Most individual mires in the district are small (100-300 ha), but they are joined together into complex systems which stretch for kilometers and are often very difficult to break up into sites. Such systems cover thousands of hectares and comprise small lakes and forest lakelets, as well as fragments of forest on mineral soil areas which are gradually growing paludified".
Fig. 3.Forest deterioration due to paludification
The authors report that "...typical fens are very rare in the area, occurring only around local carbonaceous bedrock outcrops (Lake Hijsjärvi area (Brandt, 1933), as well as near Suistamo and Leppäsyrjä), and are crucial for nature conservation. Small mire or botanical nature monuments comprising undisturbed mires with surrounding forest are to be established there".
Volkov A.D., Gromtsev A.N., Yerukov G.V., Karavaev V.N. et al. Ecosystems of the NW mid-taiga landscapes (structure, dynamics). Petrozavodsk, 1990. 284 p. (in Russian)
Gromtsev A.N. Landscape-related patterns in the structure and dynamics of mid-taiga pine forests in Karelia. Petrozavodsk, 1993. 160 p. (in Russian)
Volkov A.D., Gromtsev A.N., Yerukov G.V., Karavaev V.N. et al. Ecosystems of the western north-taiga landscapes (structure, dynamics). Petrozavodsk, 1995. 194 p. (in Russian)
Gromtsev A.N. Landscape ecology of taiga forests: basic and applied aspects. Petrozavodsk, 2000. 144 p. (in Russian)
Kuznetsov O.L., Tokarev P.N. Mires of the Suojärvi District and their resources. Suojärvi District (Republic of Karelia): economy, resources, nature conservation. Petrozavodsk, 2000, p. 24-28