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
surface calculated on the basis of the greatest crown diameter and the actual leaf surface (with coefficients of 0.8-1.4). When comparing the 400 m 2 of the 20 x 20 m area of closed oak forest with 12 m high trees having a maximum diameter of 6 m and a globe surface of 113.04 m 2 , giving a total foliage surface of 1508 m 2 , with the figures for the scrub woods with 4 m diameter, average globe surface of 50.24 m 2 and a total foliage surface of 553 nr , that is, only 36% of the foliage surface for climate-zonal closed mature forests, showing that on the south-facing slope the sustainable foliage crown surface is barely more than 1/3 of that for the climate-zonal forests. This shows a close correlation with the average water loss of the area and the difference between the climate-zonal and the average precipitation for the summer half-year in the extreme years. The role of forest litter It can be readily observed that the foliage of Quercus pubescens and Quercus cerris remaining on the trees until early winter, gradually falls during winter, piling up under the scrub woods and on the rupicolous associations and moss communities in approximately equal proportions. However, the moss and rupicolous elements, lacking a surface for permanent cohesion prevent the accumulation of forest litter so that later the spring winds carry the litter from the alternately dry and wet moss associations and sprouting grass into the scrub woods where it finally settles permanently. On a 2 x 2 m sample area of rupicolous association, it was found that of 200-300 leaves in December, only 10-40 remained until early spring (2nd April) and on the patches of moss and lichen examined, covering 1/4 m 2 (Fig. 4) in most cases none remained at all. This is quite natural, for in the case of these photophil species, the plants would die if the litter were to cling to them. Because of its relevance, reference should be made to one aspect of the author's investigations (to be discussed later in another paper) that led to a finding which is contrary to the concept of woodland and herbaceous undergrowth "association". In their post-glacial state the Central European forests lack the genuine forest herbaceous plants and the species of shrub undergrowth that give variety and deep shade distributed in fine gradations, in contrast, for example, to the subtropical temperate zone forests of Eastern North America or Japan and China. In our region, the forests consist of a few species of trees and the poorer the growth of woody vegetation the richer the variety of herbaceous plants, that is, in the vicinity of the "lower too dry", the "lower too wet" and the "upper too cold" forest limits, while it becomes poorer in inverse proportion to the growth of forests with developed tall trees giving deep shade and a high product (nudum beech and nudum oak forests). This is due to the thick layer of the forest litter and the little light with which the woody species force those of both the "too wet" (meadow) and the "too dry" (rupicolous) lower forest limit out of the forest associations, leaving only a few geophyte and acidophil species. This is particularly striking in the case of the forest zones where the litter is b own away and those where the litter accumulates due to microtopography where, in the acid areas with a low (or low utilizable) lime content (sandstone, granite, basalt, basaltic tuff) the silicate type acidophil rupicolous associations, and in the case of limestone and dolomite the calciphil, basiphil rupicolous elements indicate the survival of the elements of a rupicolous type vegetation from the postglacial forest-free period beneath the forest. The role of the meadow species of the "too wet" lower forest limit can be interpreted in the same way in the case of the Querco-Fagea elements (Dactylis glotnerata, Veronica chamaedrys etc.) below the cool mesophil woods. These observations are important for the evaluation of the concept of "forest-steppe" that is not justified with sufficient criticism. In the case of scrub woods this is particularly striking: the forest litter preserving soil humidity and forming the soil with good water retention capacity is what preserves the patch of wood and the interior of the scrub wood barely tolerates herbaceous species (Geum urbanum, Dactylis glomerata ssp. aschersoniana, Dictamnus albus, Alliaria officinalis ), while in the edge of poor soil, that is the „ailing wood" the range of scrub wood species increases sharply with the penetration of the rupicolous elements. The rupicolous associations, surviving in part as forest undergrowth, thus indicate the poverty of the forest and are not forerunners of succession but, on the contrary, precisely because they prevent forest litter from settling, they impede the development of soil in a forest direction, consequently are "hostile" to the forest.
