Pekka Pakarinen , Stephen Talbot

Aapa- ja kohosuokasvillisuudesta suuren Orjajärven lähistöllä

Pakarinen P., Talbot S. Aapa- ja kohosuokasvillisuudesta suuren Orjajärven lähistöllä.

English title: Observations on the aapa-mire and raised-bog vegetation near great Slave lake, Canada

Tiivistelmä

Observations are presented from an excursion made by the authors in 1973 to the peatlands in the vicinity of Heart Lake, located 40 to 50 km west of the city of Hay River in the Mackenzie District, N.W.T. Two mire complex types were distinguished, namely aapa-mires and raised bogs. Apparently referring to similar peat-land types, Zoltai et al. (1974) have used the terms «string fens» and «peat plateaus», respectively. The extensive aapa-mires of the study area (southwest of Great Slave Lake) have a reticulate structure, i.e. the strings (= peat ridges) form a continuous net which alternates with wet flarks (= rimpis). It is noticed that aapa-mires with similar surface pattern have been described from N. Finland just south of the palsa mire zone (Ruuhijärvi 1960). Due to the calcareous nature of bedrock, the aapa-mires in the Heart Lake area studied are strongly minerotrophic (eutrophic). Particularly the moss species, but also many vascular plants allow a comparison to the mire types in northern Finland; such homologues are for example the «Rimpibraunmoore», «Campylium stellatum -Braunmoore» and «Braunmoor-Reisermoore» described by Ruuhijärvi (1960). Special attention was paid to the plant species indicating a transition from minerotrophic (aapa-mire) to ombrotrophic (raised-bog) conditions. «Fen windows» or minerotrophic hollows (cf. Sjörs 1963) in raised-bog were characterized by Carex aquatilis and Sphagnum riparium. In the marginal parts of the raised bog, several sedge species, Equisetum spp., Betula glandulosa and Larix laricina were the last remaining indicators of minerotrophic effect. Tamarack (Larix) is relatively easy to identify also from aerial photographs and therefore it could probably be used in mapping extensively bogs and fens in the northern boreal (or subarctic) zone. Trichophorum caespitosum, Drosera anglica and Carex limosa were commonly found in the minerotrophic peatlands visited, but these species were lacking in ombrotrophic sites with comparable water level. In less continental climate — e.g. in Ontario (Sjörs 1963) or in Finland — these three species are, however, frequent components of ombrotrophic bog vegetation. It is assumed that the low nutrient content of mire water in northern continental raised bogs restricts the occurrence of many species to minerotrophic sites. The vegetation of treeless bogs in the Heart Lake area will be treated in detail in a future publication (Talbot & Pakarinen, in prep.).

Vastaanotettu 31.10.2017 Julkaistu 1.1.1976

Katselukerrat 524

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