I’ve always been a big fan of urban hedges. I reckoned that – like trees – they must help manage water runoff and moderate temperatures.
Planting relatively large numbers of mixed native plants together in cities had to be good for wildlife too – maybe even more so than trees because of their diversity, volume and value as a wildlife corridor and resource. I had supposed – partly because of that – hedges in cities would also be good for human mental health.
It turns out that they have much more significant and direct benefits.
We have thought for a while that trees can reduce particulates from, for example, car exhaust. The plants either absorb them through their stomates or catch them on their leaves, to be washed off or fall to earth in the autumn. Earlier studies suggested that well positioned trees could reduce particulates by up to a quarter.
It makes sense that hedges should be pretty good at this too. They’re not only denser but also at a better level to intercept exhaust fumes. A recent study supports earlier findings supporting this. Although its efficacy varies according to conditions, a roadside hedge can reduce near road air pollution by up to over 60% in some cases (including the cancer causing pollutant black carbon). Remarkably, hedging is not only much more effective than trees, but also seems to be more effective on its own than in combination with trees.
We have a massive problem with air pollution in our cities. The UK has regularly breached legal standards in London. Many thousands are dying from the consequences, and heart breaking individual stories are emerging. A recent WHO report found that over 4 in 10 primary school pupils in the UK are breathing dangerous traffic generated particulates.
The government seems short on practicable ideas to tackle the issue, at least in the short term. Why not plant hedges?
We recently planted this specially selected triple width mixed native hedge at a school in Yorkshire. It will be a dense filter (and impenetrable barrier!) soon enough, running over 100m along the school’s boundary.
Planting hedges in cities is simple and cheap, and they are demonstrably effective at reducing harmful pollution. Mixed native hedges like you would find in the country are attractive too, with lots of wildlife value. What’s not to like?