Kitaibelia vol. 4 – no. 2. (1999) p.343-346.
Chorológiai gradiensek a Duna-Tisza közi erdei flórában
Fekete Gábor – Kun András – Molnár Zsolt
Historical floristic data drew our attention to the fact, that the distribution of the vascular flora, first of all that of the forest flora at the Danube-Tisza Mid-Region is far not uniform. Area boundaries of certain species are denser at the northern part of the area. Several species reach the southern boundaries of their regional geographic ranges here. Therefore distribution analysis was performed on the forest flora. Local distributional maps of 119 species were constructed. On the basis of visual studies and comparative analysis of area images, the following local area-types were distinguished:
Type 1. Species distributed from the foots of hills of the 'Középhegység' (Hungarian Range) by and large to the line of towns Dabas and Cegléd. This area involve numerous beech and continental oakwood elements (Asarum europaeum, Inula conyza, Hypericum hirsutum, Cornus mas). See Map 1. 15 species, 12,6 % of the total.
Type 2. The overwhelmig part (at least 80 %) of the occurrences can be found from the foots of hills of the 'Középhegység' to the south as far as the towns Kecskemét and Kiskunfélegyháza. The majority of mesophilous hornbeam (beech) wood species (gallery forest species not included) and dry oakwood elements reach their distribution limits here (Lathyrus niger, Vicia pisiformis, Lychnis coronaria, Doronicum hungaricum, Viburnum lantana, Galium odoratum, Galeobdolon luteum, Quercus pubescens, Q. cerris). See Map 2. 49 species, 41,2 % of the total.
Type 3. At least 60% of the data like at type 2., but sparse occurrences at southern part of the Danube-Tisza Mid-Region can be found as well (Galium mollugo, Euonymus europaeus, Viola cyanea, Lithospermum officinale, Iris variegata). See Map 3. 35 species, 29,4 % of the total.
Type 4. More or less the same density of occurences can be observed at the whole Mid-Region. In this group forest species, specialists with narrow sociological affinity can hardly be found. Several species form separate thickets (Berberis vulgaris, Crataegus monogyna, Ligustrum vulgare, Prunus spinosa), or occur in shrubs and rarely in grasslands (Hieracium umbellatum, Vincetoxicum hirundinaria). See Map 4. 20 species, 16,8 % of the total.
The flora gradient outlined above can be explained by parallel climatic and geological phenomena. The so called semiaridity water deficit index useful in revealing fine differences in forest steppe climate increases similarly in NW-SE direction (Borhidi 1993). On the other hand it is known that the layer thickness of sand -of the most wide-spread substratum in the area shows an increase also in the same direction while its colloid content decreases. Besides, the closeness of the 'Középhegység' should also be taken into account: this forest region may counteract as a continuous propagulum source.