Even though there are many seemingly obvious benefits to Green Bridges very little of the literature that provides hard evidence or reasoning as to why they are or should be constructed. While roads have long been identified as a major public health concern, the most common focus of Green Bridge research is the wildlife functionality and benefits, suggesting this is their main purpose. Sadly, findings in this area of study aren’t often associated with the level of financial investment that is required to build a Green Bridge, and could be a factor in the reluctance to fund more of them. However, cheap alternatives don’t always mean cheerful and sometimes ends up costing more! Wildlife crossings are no exception. The wildlife crossings currently installed on Britain's roads are often species specific with low success rates, visually industrial and in exposed locations. For example, the most common bat crossings/ gantry design in the UK are made from steel wires with plastic spheres dotted along them intended to be acoustic guides for bats. A study in Cumbria found that "bat gantries were ineffective and used by a very small proportion of bats, even up to nine years after construction. Most bats near gantries crossed roads along severed, pre-construction commuting routes at heights that put them in the path of vehicles. Crossing height was strongly correlated with verge height, suggesting that elevated verges may have some value in mitigation, but increased flight height may be at the cost of reduced permeability.” This caused much uproar and bad press, not ideal when in theory it was for an extremely good cause. However, they concluded “Green bridges should be explored as an alternative form of mitigation. Robust monitoring is essential to assess objectively the case for mitigation and to ensure effective mitigation."
The first aspect Green Bridges are most likely to have a direct impact on is animal mortality. By inserting a safe route across major roads for neighbouring wildlife, roadkill will reduce and subsequently improve safety for road users. Due to the upward trend in vehicle usage relative to population growth and the subsequent expansion of road infrastructure, roadkill is a serious conservation concern. Thus, identifying locations for Green Bridges that would most benefit fauna and flora alike, is essential in the conservation and restoration of our environment and its residents. Part of the issue is it is not deemed important to report a pheasant or a pigeon, like a deer or a badger. Project Splatter, a citizen science project based in Cardiff have provided the means to tackle this. People are able to download the Project Splatter app on their phones and report roadkill as they see it, ultimately building a database. This provides a better understanding of which roads are significantly impacting on which wildlife. However, scavenger activity and other factors resulting in the disappearance of individuals hit still accounts for a low estimate on the overall impact roads have.
Bridges not branded solely as ‘green’ but acknowledged for being multipurpose are often praised, although the detail regarding said purposes ranges and is often limited. Such as the Mile End Bridge in London that was built to connect fragments of urban park, it also proves a water recycling function via tanks either side of the bridge. However, like many other bridges with water collection functionality, it is only locally considered to benefit that bridge. Whilst arguably the irrigation systems are only utilised by the vegetation living on those bridges, it does in fact provide a much wider secondary purpose. The resident foliage flourishes, connecting local habitats and colonies to create an attractive crossing point. This crossing point is not only utilised by larger animals and humans, but also pollinators.
Mile End Bridge, London
Ecosystem services rely on a combination of natural processes to remain sustainably viable for human use. Although there is not much published evidence relating to green bridges and their ecosystem services output, the 2015 Natural England: Green Bridge Report does identify the services they would inadvertently provide. Including: Trees, standing vegetation, peat stores, species diversity, water cycling, cultural heritage, recreation and tourism, aesthetic experience and as mentioned above, pollination. So even though we can undoubtedly forecast the multitude of benefits that Green Bridges would provide, it is still important to conduct investigations that can deliver this evidence.
Road to NoKill is a campaign pushing for the reconnection of the UK’s landscape through the incorporation of Green Bridges. Not only in conjunction with the building of new roads, but also retrofitting on the 31,400+ miles of main road already fragmenting habitats.
Follow us on Facebook to find out more www.facebook.com/RoadtoNoKill
Cumbria Bat Gantry Study: http://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC3374807&blobtype=pdf&fbclid=IwAR2Tf8_fKk3Hr9UtS-G6GuHCSNzhGot6zpGdXvE728HTxc2j3Tu4bcn0T9I
Written by: Louise McGowan