Dynamik der Uferflora in einem Abschnitt der mittleren Elbe zwischen 1999 und 2007

Abstract

Krumbiegel, A.: Dynamic of the river bank flora of a part of the middle course of the River Elbe. – Hercynia N.F. 41 (2008): 63 – 82.The species inventory of the river bank of four partial areas at the middle course of the River Elbe between Havelberg and Wittenberge was investigated twice annually over a period of nine years. As a result detailed information about species dynamics both between following years and between the beginning and the end of the period are available. The species numbers of the whole investigation area fluctuate between 119 and 144. The species numbers of the four partial areas are rather similar in relation to each other over the years. 122 species were found in the first year in the whole area. The cumulative species number only slightly increased after the third year, and it had an amount of 190 taxa in the ninth year. 158 (82.7 %) of these species were found in seven to nine years, so that they can be considered as highly persistent. The similarity (Jaccard) index of the species inventory of the whole area moves between 0.71 and 0.83 (following years). It has an amount of 0.61 comparing the first and the last year. Vegetation classes with most species present in the area are Bidentetea (22), Molinio-Arrhenatheretea (34), Artemisietea (26) and Chenopodietea (19). Bidentetea are present with 22 species having the highest presence level (27.0), e.g. the highest average presence (number of occurrence in the different partial areas and years - maximal number 36,0: 4 partial areas x 9 years), followed by Agropyretea- (8) und Agrostietea-species (15) with an average frequency of 25.1 and 24.5 species, respectively. 11 archaeophytes and 27 neophytes were recorded during the nine years. Some of them occurred only rarely and belong to epecophytes but 21 species are agriophytes. Some of them were present with only few individuals but in several years. Others are very common forming stands, such as the neoendemic species Eragrostis albensis and Xanthium albinum. The Elbe flood in 2002 caused the expectation of a conspicuous, at least temporary increase of the species number. However, this could not become confirmed. On contrary, the species numbers (whole area and partial areas) were the lowest ones of the whole investigation period in the year after the flood. A comparison of the investigated course of the Elbe River with other ones shows similarities as well as differences concerning the species composition. Differences are caused by stand conditions, such as different adjacent biotope types. However, despite of the same or similar conditions several species could never be found in the own investigation area. The presence or absence of those species is obviously influenced by accident. Stochastic events play a major role in highly dynamic ecosystems such as rivers close to nature and they are one of the most important factors influencing the species composition.