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Aquatic vegetation and its recent succession in the waterfowl wetland Koijärvi, S. Finland
HEIKKI TOIVONEN and CARITA NYBOM
Annales Botanici Fennici
Vol. 26, No. 1 (1989), pp. 1-14
Published by: Finnish Zoological and Botanical Publishing Board
Stable URL: http://www.jstor.org/stable/23725475
Page Count: 14
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The aquatic vegetation in the water area of representative waterfowl wetland, Koijärvi (60°58'N, 23°44'E), was mapped with the aid of aerial photographs in 1979, 1982, 1984 and 1986, in order to study the response of the vegetation to the changed water level (about 10—15 cm lower than in the late 1970s). In the shallow homogeneous lake basin with soft mud bottoms, the aquatic vegetation is abundant, but the species number low. The largest plant community is floating-leaved vegetation dominated by Potamogeton natans, Nuphar lutea and Sparganium emersum, with a considerable admixture of submerged plants (Potamogeton obtusifolius, Utricularia vulgaris, Sparganium minimum). Equisetum fluviatile also forms large dense stands. The vegetation maps revealed clear expansion of helophyte and floating-leaved vegetation. The area of the Equisetum stands had increased three-fold (from 1 to 2.7 hectares) in 7 years. Typha latifolia had also invaded shallow water locations. Short-term succession caused by muskrats (Ondatra zibethica) increased the plant diversity in the closed Equisetum stands. The swamp margins bordering the water area revealed many small local changes due to the action of ice, wind and muskrats. Spread of vegetation from the lakeward margins to the water area was usually limited, and successful only in places where the plants could become rooted in the bottom.
Annales Botanici Fennici © 1989 Finnish Zoological and Botanical Publishing Board