B. Papp szerk.: Studia Botanica Hungarica 36. 2005 (Budapest, 2005)

Szollát, György; Standovár, Tibor: Botanical values of the Öreg-hegy and Juhász-halom near Csomád

260 m) that lies west of Csomád. These hills are built up of Miocene (Karpatian = Late Burdigalian stage, Egyházasgerge formation), i.e. calcareous sandstone with Chlamys (RAINCSÁK 2001). PÉCSI (1958) and RAINCSÁK (2001) reported the presence of calcareous sandstone with Bijozoa from the Magas-, Disznó-, and Hátulsó-hegy (Magas, Disznó, and Hátulsó Hills) near Csomád (Fót formation), which is a major rock type on the Somlyó-hegy near Fót. PÉCSI (1958) also described the fossil-rich loosely cemented gravel and breccia of the Burdigalian (= Karpatian) stage from the western slopes of the Somlyó-hegy near Fót. Since both formations of this period are present in our study area, it is not surprising that the rock we collected on the northern slopes of the Öreg-hegy turned out to be gravely sandstone with Pecten belonging to the Fót formation (NAGYMAROSY, A. and SZENTPÉTERY, I., ex verb.). This formation is characterised by higher carbonate content and more solid cementation than the Egyházasgerge formation. The hill is surrounded by Quaternary gravelly-sandy deposits that extend to the foothills. Further to the northwest, Juhász-halom - in addition to Lower Miocene sandstone and Quaternary slope deposits - is built up of mixed deposits of gravel, sand and loess (RAINCSÁK 2001). (Juhász-halom in fact is a small hill of 190.4 m in height northwest of the Öreg-hegy. However, not having any official name, in this paper Juhász-halom refers to the whole valley between the Juhász-halom and the Öreg-hegy). This area - being located in the border zone between the Nagyalföld (Great Hungarian Plain) and the Északi-középhegység (North Hungarian Mountains) - is characterised by a transitional climate. Summers are less warm than in the plains due to higher elevation, neighbouring higher mountains and to the relative proximity of the Duna-völgy (Danube Valley). However, annual temperature regime with considerable temperature differences is closer to that of the continental lowland due to the combined basin and highland effects. (Since this description characterises the Gödöllői-dombság, and our study site is located at the edge of this region, the above climatic characteristics might not be completely accurate). The distribution of annual precipitation (550-600 mm) shows a continental character, though slight Submediterranean patterns can also be traced in some years. Maximum precipitation of early summer (May-June) is followed by a dry (semiarid) period (PÉCSI 1958, ZÓLYOMI 1958, FEKETE 1965). In phytogeographical terms the study area belongs to the Neogradense floristic district of the Matricum (North Hungarian Mountains) (SOÓ 1964, PÓCS 1981). The potential vegetation of calcareous sand covering the valleys and lower parts of the hills is assumed to be similar - not identical - to the sand grasslands of the Duna-Tisza köze, whereas that of sandstone slopes is similar to the steppe vegetation that we find on the southern slopes of the North Hungarian Mountains. This