Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 79. (Budapest 1987)

Debreczy, Zs.: Fluctuating-dynamic equilibrium of photophil, xerophil rupicolous plant communities and scrub woods at the lower arid woodland limit

graphs (JAKUCS 1972, p. 89-91). This area is located 130 km SW from Budapest, on the south-eastern slope of Péter Hill (at 260 m) above Balatonarács (Balatonfüred), on Middle Triassic Megyehegy dolomite, with inclinations varying from 15 to 20°, right at the edge of a sharp incline of 50°. According to the precipitation recording station that operated here until recent years, the volume of precipitation here is 602 mm, the mean average temperature of the macroclimate in the summer half-year is 17.5 °C and in the warmest months it is 21-22 °C. According to the local climate measurement data on the south-facing slope, the corresponding figures are 24 °C and 30.4 °C. A detailed geological description of the area has been given by LÓCZY (1913), and botanical and phytocenological surveys have been made by BORBÁS (1900), JAKUCS (1961) and DEBRECZY (1966-1985). The surrounding plant associations are the following: "pioneer" moss association Mannio-(Grimaldio-)Tortelletum inclinatae. (BÍRÓ & DEBRECZY 1985, 1987; Fig. 4) open and closed rupicolous associations, ChrysopogonoCaricetum humilis minuartietosum, botriochloetosum (DEBRECZY 1965, Figs 6-7); scrub woods, Cotino-Quercetum (JAKUCS 1961; DEBRECZY 1967, Figs 5, 6, 7, 10, 12, 14) lower and higher type (climate- and extrazonal subassociations) of manna ash-pubescent oak wood {Orno-Quercetum coronilletosum, petraeetosum: DEBRECZY 1967, 1968; Figs 8-9), Turkey oak forests, Quercetum petraeae-cerris in the lower situated areas covered with loess (DEBRECZY 1967) and hornbeam and oak associations Quer co-Carpinetum (DEBRECZY 1966) on the valley sides facing north. Methods used — The author analysed the scrub wood together with the ring ("Saum") of Cotinus coggygria and found Quercetea and Festuco-Brometea species in a proportion of 40% each, clearly showing the state of these scrub woods midway between woodland and rupicolous associations. The same thing can be detected on the basis of an analysis of the species composition, determining the proportion of common and separating elements, conducted on the basis of the similarity coefficients for the rupicolous associations and the woodland associations (RAMSAY 1964). Soil tests were also conducted, together with measurements of the microclimate and local climate (some with instruments on loan from the Meteorological Institute), partly with the help of outside assistants, supplemented by periodical measurements of soil humidity

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' (Figs 12-13). Parallel with the precise measurements, the author observed the behaviour of the Cotinus ring ("Mantel", "Saum") and compared these findings with other observations made in the field of dendrology, namely the frost damage in subtropical elements found in the Mediterranean region and in genuine subtropical elements, due to the poor utilisation of the available heat caused by lack of water

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' (DEBRECZY 1981; FEKETE in FIORTOBÁGYI & SIMON 1981). Climatic relations at the edaphic-microclimatic semi-arid woodland limit The local and microclimate measurements showed that the local climatic values and especially the microclimate values on the south-facing slope of the area studied are considerably higher in the summer half-year than those recorded at the Arács and Tihany macroclimate measuring stations (Figs 19-20). The quantity of water stored until the spring rapidly evaporates under the influence of the dry spring winds so that it is available mainly only to the rupicolous associations and the moss associations (BÍRÓ & DEBRECZY' 1985, 1987). The spring growth of the woody vegetation from mid-April falls in the summer half-year, during which period the average precipitation in the area over a period of years is 300 mm. Considering the fact that this is distributed unevenly, often in the form of showers and heavy rains lasting for several days, the loss of water on the south-facing slope with a gradient of 15-20° is very high: according to the measurements made, 1/3 runs off the surface and a further 1/3 seeps down into the deeper layers of the soil by gravitation. Because of the very slow absorp*> The author takes the opportunity to thank Hein van Hits (Catholic University Amsterdam) for financial assistance for the Registration Station, Ferenc Glavák for the reading of the meteorological instruments placed on Péter Hill, István Zimányi for the construction of an instrument to measure soil humidity operating on the basis of differences in tension, and IstvánRácz, Gyöngyvér Biró and Erzsébet Fráter for their conscientious work in the microclimate and soil humidity measurements. *) In the course of experiments in the introduction of exotic plants, the author has found that the hardiness of subtropical and relic subtropical elements found in the Mediterranean region with a long growing period and requiring a large amount of heat, with a tendency to recurrency, changes if the plant is able to make effective use of the heat available during the growing period, that is, if the supply of water is continuous. Where this is not so, due to the limited supply of water, the 2nd and 3rd vegetational stages are shifted to the autumn and the beginning of winter and the plant suffers severe frost damage to the cambium and some cases shoots. If this is repeated too often the plant is weakened and eventually dies. This is the reason why evergreen arborescent species of the Mediterranean type are hardier in warm locations with a damp soil (in a water-reataining trench retaining subtropical conditions) than they are on a dry slope (similar to their nativehabitat).