- environmentally harmful, intensive land use not take 100% of the surface within a spatial unit, but should keep sufficient space available for relieving or buffering uses (10 – 15%);
- to avoid large, uniform surfaces, the prevailing land use be diversified in itself; this should apply both to agricultural land and to urban areas;
- in an intensively used unit, at least 10% of the area be kept in, or developed to a “nature-emphasized” state, as is possible with netlike distribution.
The issues raised under 1 and 3 could be partially identical, or overlap, but there are different objectives (Haber, 1998, 60). Other authors have adopted this concept, e.g., Buchwald (1982*, Figure 2*). He assigned protection categories to different landscape elements.
This approach is also supported by the concept of a tiered target system of nature protection at 100% of the area (Plachter, 1991). There, Erz (1980) distinguishes four stages of the influence of nature conservation, ranging from strict nature reserves to extensively used areas and land which could be opened for additional intensive land use. On the latter, however, a minimum diversity of habitat conservation should be preserved by accompanying measures, or restored.
All these concepts emphasise the need to integrate the entire area of the landscape into the effort to maintain biodiversity. In this sense, dynamic conservation and development strategies for the cultural landscape must be found. More attention should be paid to ecosystem-specific development processes (succession) and spatial-functional aspects, as they play a key role, particularly for animals. Nevertheless, the designation of protected areas is evidently still necessary. They are included in the above concepts as a system of “core areas” for the protection of hard-to-renew ecosystems, i.e., those with long development periods, and to preserve severely threatened elements of nature. But it is absolutely necessary to include the surrounding landscape. This means that there is not only a need for a large-scale ecological network (see below) outside of the core areas, but also for the preservation of a minimum share of small-scale structures. For example, in agricultural areas, field edge structures are particularly important as habitats for the preservation of biodiversity, both between the fields towards neighbouring areas with other land use types (Hietala-Koivu et al., 2004, 75). “A minimum of border structures amounting to at least 1 – 2% of the total agricultural land area can be justified on the basis of the data in the literature.” (Knickel et al., 2001, 46). Also, the German Federal Nature Conservation Act (BNatschG, 2009*) stipulates a minimum percentage of such elements (§5 (2) and §20 (6)). One example is provided by the landscape framework plan in Mecklenburg-Western Pomerania, where regional minimum densities of landscape elements are defined (Müller et al., 2008*). Using a GIS based on available digital data, regional densities of structures were determined and objectives for regional minimum densities per spatial unit were quantified. For approximately one third of the municipalities, an urgent need for the enrichment of landscape elements was ascertained.
What do the findings from these various studies mean for nature conservation? First, it is clear that the landscape level requires much more attention. Understanding the importance of the landscape matrix is important for the conservation of biological diversity. A variety of studies have shown that the protection of the widest possible diversity at the landscape level and a corresponding control of the development of the landscape matrix is more effective than the protection of individual species and habitats (Franklin, 1993*). At the species level, however, it is difficult to develop general conservation strategies while managing a variety of species, as different demands on the vegetation or on landscape features and territorial claims often lead to conflicting objectives (Rey Benayas and de la Montaña, 2003*, 365; Howell et al., 2000, 559). Against this background, there is a growing consensus that the landscape level is the most important level for the management of biodiversity. Conservation strategies must therefore be implemented at this scale to be successful (With, 2005*, 240).
In a system of graded protection intensities of the entire landscape, protected areas certified as “core areas” are still important, but these should be designed to be significantly larger than is currently the case. So far, only a few reach the threshold of effective habitat size (Wiersma et al., 2004*, 783; Schmitt, 2004, 94; Kaule and Henle, 1991, 17). Particularly in relation to possible changes that may result from climate change, the goal of protected areas should be to maintain as high as possible a level of ecosystem diversity, with a maximum of ecological gradients, and thus maximum biodiversity (Swenson and Franklin, 2000, 714; Juutinen et al., 2008, 3750–3751). The effectiveness of protected areas for the conservation of biological diversity is, however, affected not only by size but also, and essentially, by the landscape matrix of interdependent connectivity, and by human activity in the surrounding area (Franklin, 1993*, 202; Wiersma et al., 2004, 773; With, 2005, 240). Therefore, for the designation and management of protected areas, such factors at the landscape level as land use types and intensities, or landscape and habitat change in relation to the population density in and around the protected area, should be considered. In the surrounding landscape matrix, small and medium-sized areas located close together are needed (Franklin, 1993, 203). This it is not achievable only with protected areas, but must be considered in the context of the management of traditional agricultural and forestry systems outside of protected areas (Rey Benayas and de la Montaña, 2003, 366).
Opinions differ somewhat with respect to the importance of protecting natural spatial diversity. Although it is often argued that the protection of geomorphological heterogeneity could be an efficient strategy for the preservation of existing and potential biodiversity, it has been shown that this factor is closely linked to biodiversity in discontinuous landscapes (Nichols et al., 1998, 378). Especially in relation to long-term environmental change (e.g. climate change), landscapes with high geomorphological heterogeneity are considered important, since they have the potential for accommodating many plant communities, despite changing species composition (Burnett et al., 1998, 369). However, other voices warn against limiting efforts in protection of biodiversity only to achieving maximum possible landscape heterogeneity, as this would neglect the needs of specialised or endangered species. The high diversity of species in a heterogeneous landscape, it is argued, largely reflects the large number of generalists, which is then promoted by diversity-enhancing measures (Atauri and de Lucio, 2001, 157).
The different goals of protection of biodiversity can lead to conflicts with very real policy implications. Examples are the maintenance of ecological services, consideration of ethical principles, protection of single target species (e.g., “charismatic” large animals), the avoidance of aesthetic loss, or the protection and improvement of social and economic values. To address these problems, the goals must be described in detail, and matching indicators defined (Failing and Gregory, 2003, 123). For this purpose, specific landscape metrics can be applied to define minimum equipment numbers of the landscape. Examples include the Nature Protection Act in Germany (BNatschG, 2009) and state laws which demand the determination of structural minimum densities of landscape elements (see above), or, related to this, restrictions on the use of agricultural pesticides if minimum standards are not achieved (Enzian and Gutsche, 2004).
One of the points of departure for the design of ecological networks is the assumption that the connection between landscape elements for the conservation of biological diversity can be at least as important as their size. Landscape structures that support the connectivity of species, biological communities and ecological processes are therefore a key element of conservation in a human-altered environment (Bennett, 2003, 8). The importance of wild animal migration corridors for the protection and management of biodiversity is widely known (Hargrove et al., 2005, 361). Landscape elements in the open countryside can contribute effectively to the conservation of biodiversity as habitat islands if they are interconnected by corridors (Ahern, 1991, 139). For example, it was pointed out that connecting elements such as forest corridors or small forest patches serving as stepping stones can reinforce the distribution of species in the forest interior. The spread between the individual elements (patches) is crucial for the prevention of genetic stagnation in small populations (Noss, 1983, 703–704).
Again, however, the entire landscape matrix plays a significant role. Efforts to improve the connectivity of fragmented landscapes often focus on the remnants of natural and semi-natural habitats, and the distribution of stepping stones and corridors. However, it would often be more practical, and perhaps more effective, to reduce the virtual isolation of fragments by changing management practices in the surrounding matrix, e.g., by laying out corridor or stepping stone habitats (Ricketts, 2001, 97). Such networking is not necessary for all types, or in every case. Self-pollinating plant species have done without genetic exchange for eons. Studies by Öckinger and Smith (2008, 27) on the spread of insects also show that corridors do not necessarily have a positive effect, but that the quality of the surrounding matrix plays an important role. Even highly propagating species are relatively independent of such networking elements, as shown above.
Landscape metrics have been used to design ecological networks for quite some time. For example, indicators such as the density of landscapes elements, or metrics on connectivity or isolation, need to be stated for the configuration of landscapes. Baguette and Van Dyck (2007*, 1125–1126) show that even simple measures can be beneficial landscape tools for the assessment of landscape connectivity. Nevertheless, they advocate cautious use in generalisation of the relationship between landscapes and species (Baguette and Van Dyck, 2007, 1125–1126). Kiel and Albrecht (2004, 331) recommend especially the proximity index for habitat network design, as it allows an assessment of individual areas in terms of functional integration with the living spaces of the surroundings.
The successful protection of biodiversity requires the preservation of adequate habitats and ecosystem functioning in the context of the entire landscape complex at various spatial and temporal scales. Particularly in light of future land use changes – which will increase further – and expected climate change, landscapes with high geomorphological heterogeneity are considered important. Therefore, in planning and nature conservation, the landscape level needs much more attention than has been the case to date. An understanding of the importance of the landscape matrix and an appropriate management are important for maintaining diversity.
Protected areas should still be included in the strategy; however, they should be designated as much larger areas than before. Above all, more emphasis should be placed on their contribution to ecosystem diversity and thus a maximum of possible (potential) species diversity. The selection of protected areas, therefore, must not only focus on endangered species.
Outside of protected areas, the management of traditional agricultural and forestry systems remains a key element of nature conservation. The consideration of the entire landscape matrix should also include the preservation or development of a functioning mosaic of interconnected habitats as an ecological network associated with areas of intermediate intensity cultivation (agriculture, settlement, etc.), with a minimum number or density of small-scale, semi-natural landscape elements.
In this area, landscape metrics can help improve the theoretical foundation of the methods of landscape planning and their practical application, with the goal of sustainability (Botequilha Leitão and Ahern, 2002, 65). Examples of the use of landscape metrics in spatial planning can be found in landscape planning, in the design of ecological networks and in nature conservation. Landscape metrics can thus be used for the selection of protected areas (Sundell-Turner and Rodewald, 2008; Harrison and Fahrig, 1995), the evaluation of the landscape (Botequilha Leitão et al., 2006; Herbst, 2007), or the analysis of equipment deficiencies of the landscape (Müller et al., 2008) (see below). For example, Herbst et al. (2007, 236) examined landscape metrics for usefulness as an assessment tool in strategic landscape planning. In the range of species and communities, particularly the measures Shannon-Diversity and Edge Density were found to be useful.