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Landscape Fragmentation



Introduction

During the last 20 years, ecological research on landscape fragmentation due to transportation infrastructure and urban development has revealed a huge number of adverse effects, in particular on animal populations. Today, it is known as a major reason for the endangerment of animal populations and the extinction of species in many industrialized regions of Central Europe as well as in other industrialized parts of the world.

Since 1985, several political declarations of the German Government and its advisory committees have demanded a turnaround in the progressive degradation of the landscapes in Germany. However, the trend of increasing landscape fragmentation has continued. This calls for more efficient policies.

The issue of landscape fragmentation includes ecological processes, perceptions of the effects by society, economic land-use interests, and ethical principles. The interconnections between these aspects leads to a transdisciplinary research question:

"How can structural landscape alterations and their effects be evaluated with regard to ethical principles and the values of the persons concerned by the effects (or involved in the decision-making process)? What are the conditions for acting responsibly in the decision-making process?"

Landscape fragmentation is a growing problem. In order to find solutions, the following six questions have to be addressed (among others):

  • What is "landscape fragmentation", and by which criteria and metrics can the degree of fragmentation be characterized and quantitatively measured?
  • By which criteria can the impact of fragmenting intrusions and of different fragmenting patterns be assessed?
  • Which mitigation measures are most effective in reducing the harmful consequences of traffic and urban areas?
  • Which conditions have to be met so that decision-makers can take responsibility for landscape-fragmenting intrusions and their effects?
  • What consequences do the extreme complexity of ecological interactions and the difficulties in predicting ecological effects have for choosing a proper evaluation concept?
  • How can verifiable objectives for the future dimension of landscape fragmentation be developed and achieved?

The patterns of perception and valuation held by the participants of the decision-making process, e.g., experts from traffic planning, nature protection, and landscape planning, can be investigated by qualitative expert interviews. It is the reality of the decision makers' perspectives and judgements that determines the decisions on future landscape intrusions.

Our knowledge about the effects, however, is still limited and, therefore, has little predictive power. Dealing with these limitations is an unsolved problem. Very often, there is a "circle of immunization". It stabilizes the process of increasing landscape fragmentation by leaving uncertainties that cannot be handled routinely in the environmental compatibility studies—such as effects on genetic exchange or cumulative effects—out of consideration. Therefore, these uncertainties do not have a retarding effect on the process of landscape fragmentation. In addition, there is no commitment for subsequently discovered ecological damages such as the loss of a species as an effect of road construction.

As an answer to ecological overcomplexity (and the resulting "Tantalus problems"), the concept of environmental threat proposes to refer to appropriate characteristics of the intrusions themselves—as indicators of their potential harmfulness like, for example, persistence and spatial range of environmental chemicals—instead of the poorly predictable effects.

Suitable criteria for assessing landscape intrusions can be geometric-structural or functional such as the degree of landscape fragmentation and the reduction of landscape connectivity. 'Landscape connectivity' is defined as the degree to which landscape structure facilitates or impedes the movement of animals. For example, the quantitative landscape metric 'effective mesh size', meff, can be applied for balancing new landscape-dissecting intrusions and the removal of existing barriers—particularly in environmental compatibility studies on the level of regional planning. Furthermore, it seems to be useful for providing landscape objectives (environmental quality goals) and the development of limiting standards to curtail landscape fragmentation as a contribution to the turnaround which has been called for in political declarations.

Reference:

Jaeger, J. (2002)

Landscape fragmentation. A transdisciplinary study according to the concept of environmental threat (in German; Landschaftszerschneidung. Eine transdisziplinäre Studie gemäß dem Konzept der Umweltgefährdung). Verlag Eugen Ulmer, Stuttgart. 447 pp. (Abstract)