L. Lőkös szerk.: Studia Botanica Hungarica 27-28. 1996-97 (Budapest, 1978)

Nagy, János, Figeczky, Gábor, Penksza, Károly, Fintha, István, Molnár, Attila, Tóth, Zoltán; Kalapos, Tibor: Contributions to the flora and vegetation of the Lake Bence-tó, NE Hungary

Studia bot. hung. 27-28, pp. 151-161, 1996-97 (1998) CONTRIBUTIONS TO THE FLORA AND VEGETATION OF THE LAKE BENCE-TÓ, NE HUNGARY J. NAGY

1

, G. FIGECZKY

1

, K. PENKSZA

1

, I. FINTHA

2

, A. MOLNÁR

2

, Z. TÓTH

3 and T. KALAPOS

3 1 Dept. of Botany and Plant Physiology, University of Agricultural Sciences H-2103 Gödöllő, Páter K. u. I, Hungary 2

The Directorate, Hortobágy National Park H^t027 Debrecen, Füredi u. 67/B VII 1/32, Hungary ^Dept. of Plant Taxonomy and Ecology, L. Eötvös University H-1083 Budapest, Ludovika tér 2, Hungary Lake Bence-tó has been investigated by the authors since its discovery in 1980. Detailed vegetation map of the area has been prepared, with the indication of 11 associations currently existing in the area. Using former data and our own observation, a species list consisting of 130 plants has been prepared, 12 of these are protected. The number of the days, when open water covers the area, has been decreasing from year to year. By 1995 18 species became extinct from the lake, 4 of these were protected. Weeds from arable lands tend to intrude deeper and deeper into the area, while the average nature conservation values of the associations together with the number and the ratio of species requiring permanent water supply is decreasing. A long-term pre-reconstructional research is currently conducted by the authors in the area. This paper presents the results of the first phase of their project. Key words: peat bog, transect, permanent plots, reconstruction, protected species INTRODUCTION Lake Bence-tó is a ca 1500 m long and 70 m wide, C-shaped, silted backwater on the Bereg Plain (NE Hungary) in the environs of Takos, Csaroda and Fejércse villages (Fig. 1). It was first registered in the Hortobágy Natural Park in 1990 on the basis of ISTVÁN D. PETHE's report as a new locality for the occurrence of Sphagnum species in the Samicum. Normally, such backwaters are surrounded by forests or meadows, but for the lake Bence-tó these had been turned into arable fields earlier. Only a small fragment of Querco robori-Carpinetum hungaricum forest can be found at the lake's eastern corner. Open water was present only for one month (until the end of May) in 1995. In the Holocene, alluvial clay and silt layers were deposited onto the Pleistocene river gravel sediment of the Bereg Plain. The bed of the Tisza River gradually shifted from the eastern part of the plain towards southwest leaving a laby-