In contrast to the two natural-science perspectives presented above, the understanding of “naturalness” and “wilderness” for the general public, but also for local stakeholders, is generally broader, but also individually very different, as studies by Rink (2005) and Bauer (2005) show. This runs the risk that significant qualitative differences between the different types of urban forests may not be appropriately realized and included in decisionmaking processes, and that nature and wilderness attributes will be used with less comprehensibility. As a complement to the two science-based approaches described above for assessing the naturalness of ecosystems, fundamental differences between the different types of forests can be made generally understandable with a simple organizational approach.
The basic idea of the “four natures approach” (Kowarik 1991, 1992b) is to reduce the existing diversity of very different, culturally varying forms of nature that are found within the impact area of cities down to four types and thereby emphasize their respective “characters” (Table 2).
• “Nature of the first kind” is the “original” nature. This includes ecosystem types or landscapes that are remnants of pristine ecosystems or at least areas that still have a strong connection to pristine ecosystems despite certain uses or changes through urban impacts. These include, for example, old-growth forests, moors, some rivers and lakes, rock formations, etc.
• “Nature of the second kind” includes elements of the landscape that arose through traditional or modern agriculture and forestry practices, for example, meadows and pastures, crop fields, hedgerows, coppices, intensively managed forests, etc.
• “Nature of the third kind” comprises the greenery that has emerged through horticultural plantings, maintenance and upkeep. This includes, fundamentally, gardens and parks created during different eras of garden history, but also other urban greenery such as street trees or trees planted to define spaces in developments. This “third nature” was first recognized in the Renaissance (de Jong 1998).
• “Nature of the fourth kind” encompasses the natural development that occurs independently on typical urban-industrial sites, without horticultural planning or design. This starts with cracks in sidewalks or in colonization of walls and buildings as “artificial cliffs” and leads to growth in abandoned areas and to impressive urban-industrial woodlands.
While natures of the second and third kind are heavily culturally influenced, the first and fourth are more defined by the effects of natural processes. It is easiest to assign a wilderness character to these types (Table 2). In order to keep the fundamental differences between them transparent, one can speak of nature of the first kind as “old wilderness” and nature of the fourth kind as “new wilderness.” “New wilderness” is also occasionally used when wilderness character returns to silviculturally influenced forests or after the initiation of natural processes during reclamation activities. After the decline in forestry uses, a new wilderness development does in fact take place. It is, however, not qualitatively new, but rather involves a convergence toward an “old” wilderness. The same occurs when restoration is undertaken with the goal of approaching original conditions. In contrast, a qualitatively new type of wilderness emerges on many urban- industrial sites that, for this reason, will be described as “new wilderness” in agreement with Dettmar and Ganser (1999).
The “four natures approach” pursues two main goals through its simple differentiation:
• The first goal is, in view of the overwhelming variety of concrete manifestations of nature, to make fundamental differences between types of nature more transparent for the general public. In this way, the particular character of each type can also be better acknowledged during the planning process. To this extent, the “four natures approach” means, on one hand, an abstraction of the existing diversity; on the other hand, it also represents a qualitative differentiation, in contrast to more sweeping categorizations such as “urban green” or “urban forests.”
• The second goal is to convey, through a simple distinction between natures of the first, second, third and fourth kind, that a fundamental equivalence of values exists among the four different nature types. The original nature, Nature 1, which is identified as the “correct” nature from a scientific perspective through the application of the retrospective perspective of naturalness (see above) is therefore not automatically more valuable that the other manifestations of nature. An urban – industrial woodland can also be identified as especially valuable.
The advantage of the “four natures approach” can be summarized as the recognition of the existence of fundamentally different types of nature in urban-industrial landscapes (and beyond). It allows value to be assessed, in the context of nature conservation evaluations for example, not only in terms of traditional images of nature, such as former wilderness or traditional cultural landscapes; but also allows for a certain landscape park or even a certain form of an urban-industrial woodland to be recognized as exceptionally valuable.
The value of a certain area is, therefore, not determined beforehand according to its typological level (1 is better than 2, 2 is better than 3, etc.). Instead such an evaluation always results based on the manifestation of the type of nature at the object level. What is decisive here is the question of what manifestation or what development potential is concretely at hand and to what extent this corresponds to the particular planning or development goals.
Until now, at least in Germany, nature conservation goals have been oriented more toward the traditional image of nature (see Korner 2005). The “four natures approach” offers a perspective for new types of nature development that have been culturally influenced in various ways. It increases the chances that the social and ecological potentials of the different types of nature can be better used for the development of urban landscapes.
Wild urban woodlands resulting from natural succession on man-made sites have created a new component in the urban forest mix whose significance will grow in areas that are subjected to great structural transformation. These include many former industrial areas, but also, more generally, “shrinking cities.” A particular feature of the new urban wilderness is its position in the middle of urban agglomerations. This represents a great potential to bridge, at least partially, the often lamented spatial separation between a large part of the general public and real, existing biodiversity. This distance has grown more acute as a consequence of urbanization. Because of the significant social and ecological functions of urban-industrial woodlands, strategies should be promoted that incorporate such spaces into the development of urban green spaces. A few conditions, however, are necessary first.
It is reasonable to reconsider the often one-sided focus of nature conservation on original nature. Until now, most conservation strategies in urban agglomerations have focused on (1) the preservation of remnants of pristine ecosystems, or (2) on restoring native species in managed or ruderal habitats (e. g. Kendle and Forbes 1997; McKinney 2002). The evolution of specific urban-industrial ecosystems, especially of a new type of wild urban woodland calls for an additional third way: the acceptance of natural processes that lead to a new kind of post-industrial ecosystem. This “nature of the fourth kind” as a “new” wilderness sharply diverges from t9he traditional “old” wilderness of our pristine ecosystem relics. However, how the conservation value of ecosystem development on urban-industrial sites should be evaluated usually remains uncertain (Harrison and Davies 2002).
In Britain, former mining slagheaps have long been seen as “special sites of scientific interest” with substantial conservation value (Kelcey 1975; Davis 1976; Box 1993). A very few projects in Germany, such as the Industriewald Ruhrgebiet (the Industrial Forest of the Ruhr) or Berlin’s Sudgelande demonstrate that urban-industrial nature can also be incorporated in the development of green spaces within developed areas (Weiss 2003; Kowarik et al. 2004; Kowarik and Langer 2005; Dettmar 2005).
We know from various studies, however, that residents often have reservations about wilderness. What is partly true of traditional wilderness areas (e. g. Durrant and Shumway 2004; Bauer 2005) is all the more true for the “new wilderness” of urban-industrial woodlands. It is therefore necessary to make this new type of nature more accessible; design measures, the incorporation of works of art and an intensified work with the public may be of help. In the development of urban-industrial woodlands, as is the case in historic parks (Kowarik et al. 1998), there exists a shared area of responsibility for disciplines that often work separately from one another. In addition to nature conservation and landscape architecture, historic preservation should also be incorporated when the cultural foundation of the new nature development within post-industrial landscapes has historic preservation value. Common historic roots can be drawn upon for this, as Korner (2005) shows with the example of nature conservation, historic preservation, landscape architecture and forest aesthetics.