As post-industrial uses are often not possible in the areas affected by structural change, the abandonment of sites is a signal for the development of a new type of urban-industrial forest by natural colonization processes. In the German Ruhr, this new forest type is widely dispersed across sites of the iron and steel industries and across mining areas (Dettmar 1992; Weiss et al. 2005). New urban woodlands can emerge on other types of sites as well, for example, on old, less-maintained cemeteries (e. g. Zisenis 1996), on the rubble of former buildings (Kohler and Sukopp 1964; Kowarik 1992a; Fig. 1-5) and on rail yards that have fallen into neglect (e. g. Reidl and Dettmar 1993; Kowarik and Langer 1994; Burckhardt et al. 2003).
A few peri-urban woodlands can be equivalent to urban-industrial woodlands when industrial uses away from cities lead to significant site
Table 3. Urban-industrial woodlands result both from cultural and natural processes
Cultural processes Natural processes
Abiotic conditions
• Earlier uses have significantly altered substrates or soils have been created entirely anew
• Structural relics of earlier uses may remain in their entirety or in part
Biotic conditions
• 
Relics of earlier horticultural plantings may still be present
• Previous uses may have unintentionally introduced non-native plant or animal species
• The culturally determined species pool of the urban surroundings acts as source for the colonization of derelict sites; significant role of non-native species as ornamentals • After abandonment of earlier uses, social activities may change the vegetation and site dynamics and lead to new cultural patterns
changes. Post-mining landscapes are a good example (Tischew and Lorenz 2005). Urban-industrial woodlands generally can be distinguished through fundamental characteristics from the other types described earlier.
Habitat continuity
In contrast to the other woodland types, the habitat continuity of urban- industrial woodlands is generally very low. Forest stands, however, can develop within two to three decades. These merely decades-old stands pre
dominate on abandoned areas in former industrial regions of central Europe. As is expected with such a short development time, the soils are not yet fully developed with the result that the vegetation development is heavily dependent on the characteristics of the anthropogenic substrate. In certain situations, however, woodlands of profoundly changed urban – industrial sites may be distinctly older, e. g. those on ancient ruins, fortress grounds, or old mine slagheaps (Dickson 1989; Jochimsen 1991; Caneva et al. 2003; Celesti Grapow and Blasi 2003).
