Opinion
Measures to reduce population fragmentation by roads: what has worked and how do we know?

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Roads impede animal movement, which decreases habitat accessibility and reduces gene flow. Ecopassages have been built to mitigate this but there is little research with which to evaluate their effectiveness, owing to the difficulty in accessing results of existing research; the lack of scientific rigor in these studies; and the low priority of connectivity planning in road projects. In this article, we suggest that the imperative for improving studies of ecopassage effectiveness is that road ecology research should be included from the earliest stages of road projects onwards. This would enable before–after–control–impact (BACI) design research, producing useful information for the particular road project as well as rigorous results for use in future road mitigation. Well-designed studies on ecopassage effectiveness could help improve landscape connectivity even with the increasing number and use by traffic of roads.

Section snippets

Ecopassages: a solution to reconcile roads and wildlife

Roads and traffic have large effects on a wide range of animal species [1], and these effects can be similar in magnitude to other impacts, such as habitat loss [2]. Roads affect wildlife through several mechanisms [3]: populations are reduced through direct mortality owing to collisions with vehicles; traffic disturbance (e.g. noise, lights and motion) reduces the quality of habitat near roads (e.g. [4]); and, for many species, roads are barriers to movement owing to physical obstacles, such

Difficulty of accessing research results

A review by Pullin et al. [16] showed that most conservation actions remain experience based and rely heavily on traditional land management practices and conjecture. In fact, many management interventions remain unevaluated. Most road planning is under government ministries or departments where information, although public, is usually contained in internal reports (‘grey literature’) that are not broadly distributed. Some of this work has been reported in conference proceedings available on

What types of ecopassage work?

Various types and sizes of ecopassage have been evaluated in terms of their use by a range of taxa 33, 34, 35, including ‘green bridges’ or wildlife overpasses over the road, and wildlife underpasses extended under the road, which vary from small culverts or tunnels to larger culverts and large open-span bridges. Use rates suggest that different species preferentially use different ecopassage types, and some species require particular features in the passage. This, combined with success stories

Potential solutions for improving the impact of road mitigation research

The overarching imperative is that road ecologists and road ecology research should be involved throughout the road project, beginning with the earliest stages of planning. Transportation planning occurs over many years, even decades. Involving road ecologists throughout the process will facilitate incorporation of ecopassages into road projects, with the potential to improve connectivity across existing roads and mitigate connectivity loss on new roads. In addition, early involvement of road

Concluding remarks

Up to now, road mitigation research has mostly languished in a backwater where studies lack scientific rigor, are reported in obscure outlets and are ignored by the larger research community and the road planning community. As the impacts of roads on wildlife populations become more evident [1], road ecology is entering the mainstream of applied ecology. We anticipate that large improvements in the quality of information on road mitigation measures, such as wildlife ecopassages, are just around

Acknowledgments

This paper followed discussions at the International Conference on Ecology and Transportation held in September 2010 by the Infra Eco Network Europe. We would like to thank Miklós Puky, Andreas Seiler and Jochen Jaeger for organizing this forum and inviting researchers, planners and decision-makers to brainstorm on population viability and animal movements in human-dominated landscapes. We also thank the reviewers for their constructive comments. Work on this article has been funded by the

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