Road Ecology for Environmental Assessment

Sammanfattning: Transport infrastructure is closely linked to several politically relevant sustainability issues, and since 1985 a formalized environmental assessment process is linked to planning and construction of new roads and railways in the EU (EU directives 85/337/EEC and 2001/42). The aim of the environmental assessment process is to think in advance; to identify, predict and evaluate significant environmental changes resulting from a proposed activity, in order to adjust the proposed activity accordingly and to avoid unnecessary and unexpected consequences. Biodiversity is a component of sustainable development that is in many ways affected by road and railway construction, but which has been challenging to fully account for within the environmental assessment process. This thesis presents four studies on the role of biodiversity in environmental assessment of road and railway plans and projects. Paper I presents the state of the art of road and railway impacts on ecological patterns and processes sustaining biodiversity, and reviews the treatment of biodiversity in a selection of environmental assessment reports from Sweden and the UK. Paper II presents a quantitative assessment of the impact of the Swedish road network on birds and mammals, and how fragmentation and road disturbance might affect a selection of ecological profiles. Paper III demonstrates how scientific models, data and knowledge can be mobilized for the design and evaluation of railway corridors, and Paper IV analyses how habitat connectivity, as a prerequisite of genetic exchange, relates to landscape composition and size and number of fauna passages. The results from Paper I show that road and railway impacts on biodiversity need to be addressed at every level of planning; from corridor alignment in the landscape to utilization and maintenance. The review of environmental assessment reports shows that the treatment of biodiversity in environmental assessment has improved over the years, but that problems with habitat fragmentation, connectivity and the spatial delimitation of the impact assessment study area remain. The results from Paper II identify natural grasslands and southern broadleaved forest, prioritized habitat types important for biodiversity, to most likely be highly affected by road impacts, and suggest road disturbance to have a high impact on overall habitat availability. The results from Paper III demonstrate how the landscape specific distribution of ecological and geological resources can be accounted for in railway corridor design, and potentially lead to more resource efficient outcomes with less impact on ecological processes. The results from Paper IV indicate that the several small fauna passages would increase connectivity more across a barrier than the construction of a single large. Effective barrier mitigation will also depend on the selection of focal species and the understanding of how the focal species perceive the landscape in terms of resistance to movement. This thesis demonstrates how quantitative assessment can benefit biodiversity impact analysis and address issues such as habitat connectivity and fragmentation, which have been difficult to account for in environmental assessment. It is recommended that biodiversity impact analysis moves towards an increasing use of quantitative methods and tools for prediction, evaluation and sensitivity analysis. Future challenges include verification and calibration of relevant spatial ecological models, and further integration of road ecology knowledge into road and railway planning.