Tuula Pienimäki

Kasvillisuuden ojituksen jälkeinen kehitys eräillä suotyypeillä Pohjois-Pohjanmaalla

Pienimäki T. Kasvillisuuden ojituksen jälkeinen kehitys eräillä suotyypeillä Pohjois-Pohjanmaalla.

Tiivistelmä

The paper deals with the ground vegetation succession in different mire site types (RhSR = herbrich sedge birch-pine swamp, KN = Sphagnum papillosum bog, RiN = flark fen; for site type classification used in Fintand see Heikurainen & Pakarinen 1982) drained in 1930 s. The study sites are located in North-Ostrobothnia in the experimental fields of Muhos Experimental Station of the Finnish Forest Research Institute. Measurements of the present ground water levels as well as the basal areas of the tree stands were taken in connection with the vegetation analysis in summer 1979. Ground vegetation was analysed from sample plots of 1 sq.m applying the method used by Heikurainen (1951). The analysis data of this study were compared with the vegetation descriptions of the sites made in 1930s before the sites were drained, analyzing the degree of similarity (Jalas 1962). The terminology and concepts, used in South Finland, to describe the vegetation succession affected by drainage were also applied to this study. These terms and concepts, however, are probably not as such fully applicable in the North Finnish conditions as also indicated by the present results. Development of varying degree, depending on the site type and effectiveness of drainage, towards drier vegetation types has taken place on the studied sites. On RhSR site the mire species have almost totally disappeared, even on rather broad ditch spacing (50 m); whereas on nutrient poor, originally wet site types (RiN, KN) the ground vegetation still consists of mainly mire species, even on narrow ditch spacing (25 m). Naturally, the lowshrub and moss species of drier habitats have gained importance even in the latter case. The greatest vegetational change, however, has taken place in the, originally, very wet flark surfaces following the radical lowering of the water table. The basal areas of the tree stands varied within large limits (0.8 – 15 m3/ha) depending on the site type (fertility) and the effectiveness and condition of drainage. The ground water table in the studied sites stayed at the depth of 30-60 cm during the summer 1979. The rather fertile RhSR site can be considered to have reached the final stage of vegetational succession during the 50 years since drainage, whereas RiN and KN sites are still in the transitional drainage phase (for classification of drained peatlands, see Heikurainen & Pakarinen 1982). It seems questionable whether nutrient poor, originally wet mires, when drained, at all reach the final stage of succession in North Finland and certainly more research is needed in this field.

Vastaanotettu 31.10.2017 Julkaistu 1.1.1982

Katselukerrat 1151

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