Green bridges, also known as wildlife crossings or landscape bridges, have a number of benefits such as creating a safe crossing point for wildlife movement, joining habitats and connecting colonies, creating a crossing point for people and integrating roads and railways into the surrounding landscape.
Roads and railways can have negative impacts on the environment and a number of species. They can fragment habitats resulting in species isolation and population declines. They also fragment valued landscapes, affecting both our visual enjoyment and our ability to access green space.
A report published by Natural England – Green Bridges: A literature review - has found that green bridges can be built to carry wildlife over roads and railways to reduce the negative impacts caused by fragmentation. These bridges are usually planted with a variety of local trees, shrubs and other vegetation so animals can remain mobile despite the barriers imposed by transport infrastructures. Green bridges are common in Europe and North America, however there are only fifty six in the UK.
The design of the bridge will depend on the overall goals and landscape. The following features should be considered:
- Width and length (current literature recommends a width ranging from 25-80m)
- Suitable vegetation to be in keeping with local landscape and habitats
- Possibility of water features which can create stepping stones for species using the bridge and can also provide a habitat in their own right
- Soil depth
- Screening and fencing that can be used to reduce disturbances on the bridge from noise and light
- Ecosystem services i.e. diversity, pollination, cultural heritage and recreation
- Engineering considerations
Green Bridges could become an important part of the sustainability of future transport projects in the UK and there are a number of alternarives including underpasses and tunnels.
One example of a green bridge in the UK is the A21 Scotney Bridge. This was constructed as part of a Highways England improvement scheme for a new dual carriageway. The bridge is located within the High Weald Area of Natural Beauty. The bridge was constructed for historic landscape purposes and to provide wider ecological benefits. Dormice, a target species of the project, have been recorded using the bridge which had nest boxes incorporated into its design so that they can access habitats on both sides of the bridge.
A21 Scotney Bridge © Land Use Consultants/Natural England
In London a Garden Bridge across the river Thames has been proposed by the charity Garden Bridge Trust. The project aims to create a new 366m-long footbridge that will stretch across the River Thames from the top of Temple underground station on the North Bank to the South Bank. The bridge will link the tree lined South Bank to Victoria Embankment Gardens and Temple Gardens on the North Bank providing an ecological corridor bringing wildlife and horticulture to the heart of London. A recent study by ComRes has shown that 78% of Londoners support a garden bridge being built across the River Thames and the vast majority think that the public sector should play a role in funding a new green space in London. Find out more about the project and its current development here.
Increasing connectivity is not a new concept. Lawton’s Report – Making Space for nature- highlights the importance of ecological networks. An ecological network comprises a number of high quality sites which collectively contain the diversity and area of habitat that are needed to support species. They have ecological connections between them that enables species and their genes to move. The report summarises what needs to be done to improve ecological networks in four words: more, bigger, better and joined.
The RSPB, along with other charities, are also promoting connected landscapes. For example, the public is being encouraged to plant a number plant species to increase pollinators such as bees and butterflies. These plants act as stepping stones between gardens and other habitats, increasing the connectivity. The public is also being encouraged to create hedgehog highways this Autumn by creating holes between fences or digging channels beneath garden boundaries to allow hedgehogs to move between habitats.
Increasing ecological networks across the UK is important for the environment. Green bridges will become an important part of this goal as they provide biodiversity benefits while helping to mitigate against ecological fragmentation.