Verbreitung, Vergesellschaftung und Ökologie von Sparganium angustifolium Michx. und Sparganium minimum Wallr. in Nordrhein-Westfalen
Hildebrand-Vogel, R.; Wittig, R.
A documentation of the current distribution of the two small species of burr reed Sparganium minimum and Sparganium angustifolium in North Rhine-Westfalia shows that these two species are rightfully included in the "Red List" of endangered ferns and flowering plants in this federal state. Sparganium minimum occurs in North Rhine-Westfalia only within five quarter-quadrants of TK 25. In addition, three further incidences exist just outside the federal state boundary in Lower Saxony. There are as little as two populations of Sparganium angustifolium in North Rhine-Westfalia. A further population (Römersee) named for some time in scientific literature as an incidence of Sparganium angustifolium has been identified as a hybrid (Sparganium angustifolium x emersum). It has also been possible to identify such hybrid populations at two further sites in North Rhein-Westfalia and at two sites in the area of the border between Lower Saxony and North Rhine-Westfalia. A comparison of the two species thus shows that Sparganium angustifolium is even more endangered than Sparganium minimum. This is also expressed in the demands it makes on its habitat: the "genuine", i. e. non-hybrid Sparganium angustifolium is closely associated with low-nutrient waters. If scholarship is in disagreement in this respect, this may be due to the fact that the hybrid Sparganium angustifolium x emersum, which has previously been frequently confused with Sparganium angustifolium, displays a clearly broader amplitude, and can also be found in more nutrient-rich waters and even in slightly polluted waters. In terms of plant sociology, the incidences of Sparganium minimum may be associated with Sparganietum minimi. It is not possible to detect a clear categorization in this association from the material of our relevés. The Sparganietum minimi utricularietosum minoris has more of the character of Utricularietea, whereas the Sparganietum minimi juncetosum bulbosi tends more towards the Littorelletea. In addition to these two sub-associations, traces of a Sparganietum minimi utricularietosum australis and a Sparganietum minimi inops may be found in North Rhine-Westfalia. The Sparganium angustifolium and Sparganium angustifolium x emersum incidences may be clearly associated with the class of Littorelletea, on account of the highly perpetual incidences of Juncus bulbosus and other Littorelletea species. The stands of the non-hybrid Sparganium angustifolium tend floristically to the Utricularietea (sub-communities of Sphagnum cuspidatum and Utricularia minor), and display no clear membership in any alliance. The plant stands which are exclusively characterized by the hybrid Sparganium angustifolium x emersum, in contrast, clearly belong to the Hydrocotylo-Baldellion. In order to record the demands made on their habitat by the various communities and subcommunities analyses were made monthly in the course of three vegetation periods (1981 to 1983) of water samples to establish diverse hydrochemical-physical characteristics. In contrast to highly acidic, dystrophic and oligotrophic waters, in which the communities of burr reed differentiated by species of bladderwort and Sphagnum still exist, the water habitat of the Sparganietum minimi juncetosum bulbosi may be classified as mesotrophic, and that of the typical subunit of the Sparganium angustifolium community even as weakly eutrophic. Generally the total ionic content indicates a rising trophism.