On the phytosociology and ecology of Isoëtes asiatica (Makino) Makino in oligotrophic water bodies of South Sakhalin

Abstract

In 1989, in the southeast of the Sakhalin Island and south of the village Okhotskoye, Isoëtes asiatica (Makino) Makino and I. beringensis Kom. were detected in 24 oligotrophic lakes for the first time on Sakhalin. These are stands of the community of Isoëtetum asiaticae ass. nov. which in the majority of the lakes form a characteristic pioneer vegetation of the shallow littoral zones. In addition to poor-species dominance stands of both of the Isoëtes species, penetration stages of both of these species as well as stages rich in Comarum palustre, Eleocharis acicularis and Potamogeton species can be differentiated. Besides the structure of the species, the site conditions, particularly of the water bodies are described. The ion content is represented by absolute and relative ion field diagrams exemplified by 7 selected water bodies. The ion content is characterized by sodium and chloride which are prevailing, while calcium and magnesium as well as hydrogen carbonate and sulphate exist in low quantitative proportions only. The indicator values of individual characteristics and the complex characteristics of the Isoëtes lakes are discussed. The hydrochemical characteristics of the Sakhalin, Kuriles and Kamchatka Isoëtes waters are compared with the Isoëtes water bodies of North America and Europe. The danger to Isoëtes water bodies is discussed, necessary protective measures are defined.