Agency of natural mechanisms

The leeway for the agency of natural mechanisms is significantly greater in urban-industrial woodlands than in woodlands used for forestry or in those resulting from urban greening. The latter two are usually heavily influ­enced by the initial plantings, and by use and maintenance. On urban – industrial abandoned areas, in contrast, the ecosystem dynamics are mainly influenced by natural processes through population dynamics, succession and soil formation (Table 3; right column). In this way – depending on the extent of the changes caused by earlier uses – primary or secondary suc­cession as well as intermediate degrees can be induced (Rebele 2003). In cases where current social uses are limited or do not exist due to limited accessibility, the development of urban-industrial woodlands is fundamen­tally determined by natural processes just as it is in pristine forests. From a few studies of succession, we know that dispersal, establishment, and ex­tinction processes can effect substantial changes to the population compo­sition in time frames of a few years to a few decades, for example the re­placement of pioneer species with forest species (Platen and Kowarik 1995; Weiss et al. 2005).

Agency of cultural mechanisms

In contrast to pristine forests, urban-industrial woodlands are heavily cul­turally influenced. This is true of abiotic conditions as well as biotic (Ta­ble 3; left column). Through removal and deposition of a variety of an­thropogenic materials, the spatial and functional contact with the original soil and its hydrology is disturbed. Woodland development on many ur­ban-industrial sites is based, therefore, on a new type of abiotic site con­figuration that may deviate significantly from the original conditions. The soil development of coal-mining slagheaps is influenced by particularly low pH values, while soils that develop on building rubble may present very high pH values (Rebele and Dettmar 1996). Extensive excavations can lead to nutrient-poor substrates upon which soil formation then pro­ceeds within the framework of primary succession (e. g. Tischew and Lo­renz 2005).

Previous uses can, however, continue to influence the site or vegetation development or may remain present in the form of structural ruins. As these vary in form, extent, and frequency, clear spatial patterns often emerge in the landscape morphology or the vegetation, which make the earlier uses readable. Through the effects of natural processes, these relics, however, lose their distinctness over time. The development of urban – industrial woodlands is also shaped indirectly through the urban surround­ings. This has an effect on the species pool that provides a source for the colonization of the site.