Deposition of materials

Peri-urban woodlands are especially affected by wet or dry deposition as well as that resulting from recreational activities. The spread of nitrophi – lous species is interpreted to be a result of nitrogen deposition (Kowarik and Sukopp 1984). Muller et al. (1978) correlated the presence of high-N indicator species (Ellenberg’s indicator species) with the use frequency of forest paths by recreationalists. The distribution of macrofungi in pine for­ests can also be related to an urban pollution gradient (Tarvainen et al. 2003). Deposition from urban-industrial sources can also clearly balance out the limiting effects of the original conditions of the site. In this way, within peri-urban pine-oak forests, trees that are more demanding are spreading across what were originally nutrient-poor sandy sites (e. g. Acer platanoides, Acer pseudoplatanus; Fischer 1975; Sachse et al. 1990). The deposition of industrial materials with a high pH suits lime-loving species, especially in areas with naturally acidic soils. The establishment of the North American Mahonia aquifolia, for example, is promoted by an in­crease in the pH values from fly ash (Auge 1997).