Woodlands that result from urban greening

Stands of trees that present forest characteristics can develop from large – scale planting of trees in park areas, but also from street trees and restora­tion plantings. Because such stands are determined based on functional goals and are often designed and maintained from artistic-aesthetic per­spectives, woodlands resulting from urban greening are heavily culturally influenced.

An additional feature that differentiates this type of woodland from the two previous types is the high species diversity and the large role of non­native species in urban greenery (Ringenberg 1994; Freedman et al. 1996; Jim and Liu 2001; Kowarik 2005). The native species also often deviate genetically from regionally native plants because they are dispersed over the supraregional nursery network, which in large part imports its seed ma­terial from other, off far-removed areas. The hazel (Corylus avellana) planted in Germany, for example, usually originates in southern Italy or Turkey (Spethmann 1995).

Despite their cultural basis, woodlands of urban greenery can also be significantly shaped by natural processes. These include the natural regen­eration of tree species or the establishment of wild plants within planted stands as well as the “export” of planted species that escape from cultiva­tion. In this way, the probability of a species becoming naturalized is a di­rect function of the number of plantings (Rejmanek 2000; Mulvaney 2001). Prominent examples of this are the substantial dispersion of maple species (Acer platanoides, A. pseudoplatanus) from horticultural plantings (Sachse 1989; Webb and Kaunzinger 1993; Preston et al. 2002).

The interaction of cultural (e. g. cultivation) and natural processes (e. g. the establishment and spread of cultivated species) often leads to park- specific communities in urban green spaces. This is clear above all in old historic gardens, in which a few plant species that were cultivated in earlier Baroque or landscape gardens have survived and have, in some cases, es­tablished large populations. These can be interpreted as cultural remnants or as indicators of former horticulture (Bakker and Boeve 1985; Kowarik 1998).

In addition to new plantings, woodlands can also emerge within the con­text of urban greening through the transformation of pristine forests or woodlands used for forestry purposes. In this way, the Tiergarten park in the center of Berlin developed from an old-growth forest that experienced a period as a Baroque park in the 18th century and was redesigned in the 19th century as a landscape park (Wendland 1979). Above all, since the end of the 19th century, peri-urban parts of woodlands have been artisti­cally shaped in order to improve their social function (e. g. the Eilenriede in Hannover; Hennebo 1971).

The example of the new development Birchwood in England illustrates the opposite case: the convergence of planted stands toward a near-natural model. In the planning concept, the existing remnants and newly planted woodlands were integrated as space-creating elements. The new plantings were integrated with the existing old stands through a “naturalistic style” (Jorgensen et al. 2005).