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

The role of the Cotinus ring Cotinus coggygria, a southern, Balkan-montane, Pontic-Mediterranean, meso-, photophil flora element with a character of xero-frequency (here also scio-frequency) plays a very important role in the scrub wood. It spreads vegetatively and its network of decumbent rooting stems completely interweave the soil, forming a "polycormon system" (as rightly named by PÉNZES 1958). The last section of the polycormon at the edge of the Cotinus ring ("Saum") is characteristically xeromorphic (Fig. 17): the nodes are short and the stems are subshrub-like, that is, old stump-like sections are directly joined to the young branches and there are many dead branches younger than 10 years with an annual growth of less than 2 cm, and also many dead shoot ends and the stems regenerating from below. It can be clearly seen on the shrub that it is at the limit of its tolerance. A species requiring heat and light, it is forced out to the edge of the wood where it is exposed to great extremes. The finest shrubs and scr,ub-like examples of this species in the Carpatopannonian flora region are found on the steep rocky south-facing hillsides with a high rainfall in the north-east region of the Hungarian Central Mountains where they reach a height of 4-5 m. Here, however, it is found in xeromorphic and under the forest in sciotolerant-form, spreading vegetatively, as does the Coronilla emerus that rarely finds its right place but creeps by means of underground shoots down the valley into the oak-hornbeam forests (DEBRECZY 1966). The distribution of the species (Fig. 16) clearly shows their subtropical relationship (Cotinus obovata, C. velutina) — these two species living in a subtropical climate grow the tallest — and Cotinus coggygria grows to tree form really only in places with a subtropical local climate (Kattaro/Kotor, Abbázia) and in our parks where it is watered or on the Great Plain where there is a high ground water level. (The tallest, a tree with a diameter of 10 m and a trunk diameter of 60 cm at the base is found in a park at Tarhos on the Great Plain.) The subtropical nature of the Cotinus is very important in the evaluation of the scrub wood margin : here the plant's growth is restricted because of the drought and with the autumn rains it begins a new vegetation period, its cambium layer swells and the sudden frosts cause frost damage to the upper parts of the stems that have begun to grow near the warm, damp surface of the soil (Figs 18-19). As a result of the frosts there is often only a few mm of live tissue left in the stems and in the lower part of the branches protected from the soil (Fig. 19). Sooner or later these parts are separated from the central sections that represent the source of nourishment, becoming "satellites" of the polycormon system and subsequently become victims of the dry periods. This could be clearly seen during the drought of 1983 and 1986 when the margin dried to brittleness for a width of halfa metre, while the interior remained fully intact and fresh green in colour (Figs 14-15). This was strong proof that the wood begins to die not in the middle, but at the edge ! The instances of denudation of the interior of the scrub wood; penetration of rupicolous-elements I observed the exceptional cases where the return of rupicolous elements indicate the partial denudation of the interior of the scrub wood. These cases are the following: 1) A part of the scrub wood is specially exposed to wind from where the forest litter is blown away. 2) There is a rise in elevation on a rock basis or a shallow underground rock stratum below the scrub wood. 3) The sections rising above the layer of litter around the thickened stumps of the older trees in the scrub wood provide a place for the rupicolous elements where they are protected from the litter. 4) An erosion area passes through a section of the scrub wood, preventing the formation of rendzina. All these cases occur on a few percentage of the scrub wood patches.