Ecological bridges

Ecological bridges are engineering structures built in areas where highways, railways, or similar transportation routes fragment natural habitats, to enable safe passage for wild animals. These bridges are typically designed to blend with the natural environment through the use of soil, vegetation, and landscape arrangements, allowing animals to move between two areas without disrupting ecosystem continuity.

Habitat fragmentation caused by wildlife disruption leads to a reduction in animal habitats, a decline in genetic diversity, and the disruption of ecological balance. Ecological bridges aim to minimize this fragmentation, contributing to species conservation and reducing accidents arising from human-wildlife interactions. In Türkiye, such bridges are becoming increasingly common, particularly in highway projects.

Ecological bridge (Image generated by Artificial Intelligence.)

History and Development

The origins of ecological bridges date back to the second half of the 20th century. The first ecological crossing implementations worldwide began in the 1970s and 1980s in the Netherlands, Canada, and Germany. These structures were developed as solutions to counteract the disruption of wildlife migration routes and the interruption of inter-species genetic flow caused by expanding road networks.

In Türkiye, ecological bridges were first planned in the 2010s under the leadership of the General Directorate of Highways. The first large-scale applications were implemented as part of highway projects, particularly along the routes of the North Marmara Motorway and the Ankara-Niğde Motorway, where bridges were designed to facilitate wildlife crossings. These structures were constructed to ensure the safe passage of mammal species such as roe deer, wild boar, foxes, and red deer.

During their development, engineering and ecology disciplines have been integrated into the design of ecological bridges. Vegetation and soil cover selections have been planned to support the natural behaviors of target species. In Türkiye, ecological bridges are now designed not only to serve mammals but also to provide safe passage for reptiles and small mammals.

The widespread adoption of ecological bridges has become mandatory within environmental impact assessments. Wildlife movement corridors are now considered during the planning phase of highway and motorway projects, thereby preserving ecosystem integrity and preventing human-wildlife collisions.

Ecological Bridges in Türkiye

In Türkiye, ecological bridges are implemented primarily in regions with intensive highway development to protect wildlife. According to data from the General Directorate of Highways, there are currently eight operational ecological bridges nationwide, one under construction, and fifteen more planned.

Example Projects

• North Marmara Motorway Ecological Bridges: Designed to facilitate the natural movement of wildlife through forested areas along the motorway. Vegetated overpasses enable safe passage for mammals such as red deer, roe deer, foxes, and wild boar.

North Marmara Motorway Image (Ministry of Transport and Infrastructure)

• Samsun Ecological Bridge: Constructed specifically to ensure the safe passage of mammal species such as roe deer and wild boar. The design incorporates soil cover and native vegetation to preserve the animals’ sense of natural habitat.

• Ankara-Niğde Motorway Wildlife Crossings: Multiple ecological overpasses and underpasses have been constructed along the motorway. These structures facilitate the safe movement of local fauna and contribute to the preservation of habitat connectivity.

• İzmir–Çeşme and Bolu Mountain Motorway Crossings: Designed to ensure the safe passage of wildlife populations. Their ecological functionality has been enhanced through elements such as vegetation cover, noise barriers, and light shielding.

İzmir–Çeşme Motorway Image (Ministry of Transport and Infrastructure)

Function and Use

Ecological bridges in Türkiye provide safe passage corridors for both large mammals and smaller mammals, reptiles, and amphibians. Their use directly reduces wildlife-vehicle collisions and helps preserve genetic diversity. At the same time, ecological bridges have become mandatory components of environmental impact assessments for motorway projects and have emerged as a critical element in sustainable transportation planning.

Design and Technical Features

The structural design of bridges is tailored to the behavioral characteristics of target animal species. Overpasses are typically constructed with soil cover and native vegetation to create a landscaped environment that mimics natural habitats, enabling animals to cross safely. Underpasses are generally designed as tunnels or culverts, providing secure corridors for small mammals, reptiles, and amphibians.

Physical dimensions such as width and height vary according to the intended purpose. In Türkiye, for example, some overpasses extend up to 50 meters in width, providing sufficient space for large mammals such as red deer, roe deer, and wild boar. The edges of the structures are surrounded by barriers to reduce noise and light pollution, facilitating animal acceptance and continued use of the crossings.

Vegetation planning is a key technical component of ecological bridges. Projects in Türkiye use native plant species to landscape the bridges in harmony with the surrounding natural ecosystem. This ensures that animals not only find a safe passage but also benefit from the continuity of their habitat during transit.

Ecological and Environmental Benefits

The primary ecological benefit of ecological bridges is the maintenance of connectivity between wildlife populations, thereby preventing habitat fragmentation. Highways and other human-made infrastructure sever natural movement corridors, leading to reduced genetic diversity, increased isolation effects, and disruption of ecosystem balance. Ecological bridges mitigate these negative impacts by supporting inter-species gene flow.

Observations of ecological bridge usage in Türkiye demonstrate that mammals such as roe deer, wild boar, foxes, red deer, and badgers regularly use these structures, significantly reducing wildlife-vehicle collisions. Additionally, these structures provide safe passage corridors for small mammals, reptiles, and amphibians, contributing to the preservation of ecosystem integrity.

The environmental benefits of ecological bridges extend beyond fauna. Through vegetated overpasses and natural landscape design, local flora is also preserved, ensuring the continuity of regional ecosystem services. The presence of these structures directly supports the protection of natural wildlife migration routes, the continuation of inter-species interactions, and the enhancement of biodiversity.