Ábrahám Levente (szerk.): Válogatott tanulmányok VI. - Natura Somogyiensis 19. (Kaposvár, 2010)

BALÁZS A. & ERDŐS L.: Botanical survey of Southern Transdanubian oxbow lakes and the changes of the last 10 years

BALÁZS A. & ERDŐS L.: OXBOW LAKES 43 Table 1: The 5-graded scale and its explanation according to KOHLER (1978). Scale -values Explanation 2 3 4 very rare rare spread frequent abundant All oxbows were examined during the summer 2008 or 2009. We divided the oxbow lakes into different length sections, which was based on the variety of the habitats. The species on each sections were valued with a 5-graded scale according to KOHLER (1978) (Table 1.), and the scale-values were cubed according to MELZER (1988). We applied RPM% (Relative Plant Mass) to the data evaluation (KOHLER and JANAUER 1995, PALL and JANAUER 1995, SZALMA 2007). RPM% is the percentage of the quantity of a plant species in the ratio of the quantity of all observed plant species. This parameter gives us information about the dominance relationships. The formula of RPM% is: where RPM is the relative plant mass, M

l is the scale-value of a plant species on the ,i"-th section, L

i is the lenght of the ,,i"-th section, j is a constant of a plant species. Plant species names are used according to SIMON (2000). Evaluation of the actual state of the oxbow lakes First, we characterize the actual state of the oxbow lakes based on the dominant species, other water-weeds, protected and adventive species. Among the dominant species, Phragmites australis was the most typical in each one of the six oxbow lakes. Utricularia vulgaris was found in the highest quantity in the Vájási-tó, Nymphaea alba reached a considerable mass only in Mailáthpusztai-tó, Thelypteris palustris and Typha angustifolia were dominant in Hótedra. We found a total of seven non-protected water-weed taxa, six protected species and five adventive species (Table 2). It is worth mentioning that Mailáthpusztai-tó possesses the most protected species. Among the adventives, Solidago gigantea proved to be the most wide-spread. Below we give a comparison of the different shore sections of the oxbow lakes under study. We evaluate all six oxbows, but only the results of the Zalátai Ó-Dráva are illustrated (Fig. 1), due to space limitations. If dominant species are considered, no remarkable differences exist between the left and right shores. For example, Nymphoides peltata and Phragmites australis are dominant on both shores of Zalátai Ó-Dráva (Fig. 1). J (v/; x l, )< l oo RPM [%]= y.y ("><,) Results