Externally funded project

Bottlenecks in habitat networks (Engstellen in den Lebensraumnetzen)



Through a cabinet resolution in 2007 putting in place the German National Strategy on Biological Diversity, Germany committed itself to tackling biodiversity loss, which has been observable for decades. The aim is to stop and reverse this trend by 2020. The obvious threat to biological diversity caused by land use and habitat loss is expressed by several indicators in Germany. Among this set is the indicator “land consumption”, which reflects the success of the measures designed to reduce daily land consumption by settlement development from 74 to 30 hectares by 2020. It is not only important, however, to control the amount of new human settlements and transport infrastructure, but also to manage their location and spatial distribution. New human settlements and transport infrastructure usually develop in urban areas with little open space: in metropolitan regions, urban agglomerations, suburbs of large cities and in easily reachable areas, for example, near highways. Nevertheless, settlement expansions also take place in rural areas with the consequence of a nationwide, non-reversible loss of important habitats and habitat connections. There is an obvious demand for controls to protect these areas and regions from settlement development and sealing to preserve open spaces needed by animal and plant species to ensure their long-term survival. This refers to important and valuable habitats and open spaces connected to them. Efficient controls require knowledge concerning the location of these valuable areas in the whole Federal Republic of Germany and the location of high development pressures. The three different habitat networks – dry, wet and “valuable” forest biotopes – and the nationally significant corridors for each ecosystem are good data sets to determine the ecologically important and valuable sites in Germany. In contrast, the identification and localization of potential settlement development areas are hardly predictable, but most likely and most common is the settlement development between, directly adjacent to and within existing settlements.


This research and development project “Optimization of bottlenecks in the habitat networks” identified areas in the habitat networks which have potential for settlement development. These bottlenecks are defined as (spatially) concrete landscape sections, where connections in one or more habitat networks could be interrupted by the growing together of settlement areas. Therefore, the project focused on the identification of these areas and subsequently the rating of their importance within the nation’s ecological network and probability of potential impairment due to settlement development. For the identification of bottlenecks, the habitat networks for ecosystems (habitat networks for species of dry biotopes, wet biotopes and “valuable” forest biotopes/large mammals) were overlaid with potential settlement development areas. Potential settlement development areas were determined in GIS by using current built-up areas and traffic sites (database: BASIS-DLM) to generate new development connection within their spatial context. A simple spatial aggregation of the existing settlement and traffic areas was used to connect those areas to a distance of 1.000 m in a multi-stage process. To avoid unsuitable settlement development areas in the aggregation dataset, protected and other not suitable areas were excluded. To identify bottlenecks, the ecological interrelations representing nationwide habitat networks for dry, wet and “valuable” forest biotopes were used after minor adjustments for the overlay with the potential settlement development areas. Next, all three extensive habitat complexes (systems of habitats (FR) that are functionally connected on a large scale from 500 up to 2.500 m depending on the network) were intersected with the potential settlement development areas in GIS. To identify real bottlenecks all separating overlaying areas with a minimum size of 5.000 square meters were selected. These selections represent the first bottleneck-datasets. To ensure the consideration of important habitat connections in the systems of closely neighboring habitats, bottlenecks regarding just the core areas (FR 250 or FR 500) were searched. Together with bottlenecks of the national corridors, bottlenecks of the core areas and the extensive habitat complexes form the pool of resulting bottlenecks.


The pool of all bottlenecks contains 35.664 areas: about 55 % in the network of “valuable” forest biotopes/large mammals, 30 % in the network of wet biotopes and 15 % in the network of dry biotopes. In the resulting systematic differentiation and valuation of determined bottlenecks detailed information was used. This information is available for every bottleneck and is stored in the GIS-datasets together with spatial information about location and extent. These details come in part from the habitat network layers and the potential settlement development areas, while the remaining required information was generated. Basic information, like area size, number of neighboring areas in the habitat network, impacts on national corridors and core areas, percentage of biotope/biotope complex area, federal province and district were complemented with further information on synergetic effects (occur if two or more habitat networks are affected) or fragmentation effects (fragmentation index). This information is used for calculating network value, settlement development probability and finally the ecological risk of bottlenecks. Network value of bottlenecks depends on the direct impact on national corridors and core areas, synergetic effects determined by overlays with bottlenecks from other habitat networks and the fragmentation effect specified by fragmentation index. These 4 criteria were combined in a matrix while forming 5 classes of network value (very high, high, intermediate, subordinate (more regional) and subordinate (more local). This classification leads to the conclusion that 8 % of all bottlenecks have a high or very high network value and are therefore very important for the national habitat connectivity and biotope network. In contrast, 71% of the bottlenecks belong to classes of lesser network value. They are more relevant for regional and local habitat connectivity and should be considered at these planning levels. An attempt was made to divide the bottlenecks into separate classes based on different development dynamics during the valuation of settlement development probability. Valuation is based on current projections of spatial development, which allows estimates of future settlement development. One used projection is the environmental economic model PANTA RHEI REGIO. This model offers information about the growth percentage of new settlements and transport infrastructure in the administrative districts to the year 2030. Different projected percentage growth lead to distinguish the German administrative districts into 5 classes (with a very high, high, intermediate, low or very low percentage growth of developed area). The Land Use Scanner projection provides information about land-use change such as settlement development to 2030. This spatially explicit projection uses 100x100m raster units. Findings from the overlay of bottlenecks and projected new developments to the year 2030 were integrated in the calculation of settlement development probability. With the percentage of a (usually protected) biotope/ biotope complex area a third criterion was considered and integrated into the matrix. Thus, an appropriate and optimized calculation of development probability has been achieved by forming 5 classes (very high, high, intermediate, low and very low). As a result, 29 % of all bottlenecks have a high or very high, 23 % an intermediate and 48 % a low or very low development probability. The ecological risk of bottlenecks is determined by two factors: network value and settlement development probability. Regardless of the determination of network value, every bottleneck has a fundamental significance in the habitat and biotope network. On this account, the ecological risk is not the final but an additional result of the valuation of bottlenecks, which includes the consideration of settlement development probability. To determine the ecological risk of bottlenecks, the classifications of network value and settlement development probability were combined in another matrix with the result of building 5 “risk classes” (with a very high, high, intermediate, low and very low risk). The ecological risk of a bottleneck increases as (a) settlement development probability and (b) importance in ecological function within the statewide habitat network increase. With this valuation, a distinction in ecological risk develops between particularly valuable and endangered bottlenecks and those which are lesser important in the ecological network and lesser endangered by settlement development. Differentiation regarding the importance to habitat network allows adequate classifications of selected bottlenecks according to various planning levels. More than 10 % or 3.704 bottlenecks belong to both the highest risk classes. These areas are especially endangered by settlement development and equally essential parts of habitat network. Of total determined bottlenecks, 71,6 % belong to classes of an intermediate or lower ecological risk and are accordingly not exceptionally important for the statewide habitat network. The relevance of these areas for local and regional habitat connection systems has to be checked in all territorially significant planning processes. Chance of development of bottlenecks with a low or very low ecological risk may be low, but it should not be ruled out. Even in these areas, settlement developments could have negative impacts of habitat networks and thus require careful planning. For the purpose of illustration and appropriate interpretation of bottlenecks as well as derivation of planning recommendations, selected bottlenecks were further analyzed in case studies. A total of 10 areas were described in a rough analysis, using double-sided forms for their cartographical and verbal description. The purpose of this description is to present the concrete spatial situation and possible perspectives of each bottleneck. Available digital planning documents were used to this end. A detailed analysis was conducted for 5 (of the 10) bottlenecks involving field missions, interviews and more complex evaluations of planning documents. Detailed information of the current use, concrete significance and function in the habitat network are presented here, as well as current and future planning and perspectives.


The planning recommendations regarding the usage, handling and further requirements present in a compact form which tasks could and should result from the knowledge of bottlenecks. Primary objective of this research project has been achieved by identifying and processing the nation’s bottlenecks for disclosure to third parties. But this is merely a first step of placing the problems of an increasingly dense and extensive settlement and its effects on biodiversity in politics and society. This is a prerequisite for dealing with the problem. Planning recommendations are addressed to the different planning fields, departments and levels. They provide useful information about dealing with bottlenecks and also point out the limits. For example, it is indicated that the determined bottlenecks are not final; continual additions and verifications are necessary.

Last updated on 2017-11-07 at 15:10