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

species themselves represent high conservation value, estimated to worth 50 billion HUF based on abundance estimates and attached values by the Hungarian Conservation Act. For comparison, there are 42 protected plants on the Somlyóhegy near Fót (CSÁKY, P., ex verb.), which is much richer in different habitats. Of the 26 protected species of the Öreg-hegy 23 occurs on the Somlyó-hegy near Fót, but there are only three plant species that grow on Öreg-hegy but not on Somlyóhegy near Fót (and three other such species on Juhász-halom). It is also worth emphasising that about one-fifth of all Hungarian steppe woodland species occur in this relatively small area where there has been no semi-natural woodlands for at least 50 years (see Table 2). It is an important feature of the vegetation, that the sand steppe vegetation of the Nagyalföld reaches one of its northernmost outposts here, near Csomád. However, species composition and structure of these grasslands differ from those of typical sand steppes of the lowlands. One of the character species of this association, Festuca vaginata, only scarcely appears in this area, and several other important members of the sand steppes are also missing from here. There are at least two reasons for this: climatic and other site characteristics are not the same as in the Duna-Tisza köze. Since several of these "missing" species do occur on the Somlyó-hegy near Fót and at several locations in the Pesti-hordaléksíkság and on the Szentendrei-sziget, degradation must have also played a role in the development of this relatively species poor vegetation. Similar transitional situation could be described for the meadow steppe vegetation of the area. It is poorer in species than in the mountains (Északi-középhegység) and has different structure. Special bedrock and soil forming processes also contributed to the development of the distinctive site properties of this area. This area is peculiar, because it provides a rare example, where grasslands growing on calcareous sand and on also calcareous solid bedrock (e.g. Lajta limestone, dolomite) are in direct contact. This phenomenon is known from several locations in Dunántúli-középhegység (Transdanubia) and from the Somlyó-hegy near Fót. This situation has given the chance of migration for both lowland and upland vegetation as climate changed in the past, hence had high importance in the historical development of vegetation. However, these valuable surveyed areas have never been under protection. Fortunately, they have been nominated recently as parts of the Natura 2000 network. These locally and also regionally valuable sites are threatened by the spontaneous but potentially intensive spread of shrubs and of non-native tree species (Robinia pseudo-acacia, Celtis occidentalis, Ailanthus altissima). Another detrimental factor is the excavation of gravel and sand from the area. On top of all these, it is almost negligible, but still worth mentioning, that after designation as pro-