UK Lags Setting Soil Volume Minimums for Urban Trees

Ipswich trees

This article, by our own Steve Chatwin-Grindey originally appeared on the UK Green Building Council’s “Opinion” blog. -LM

In an article in the Green Property section of the Telegraph a few weeks ago, Sarah Lonsdale drew attention to the efforts of conservations, charities, and planners who are advocating for trees to be given the same status as other forms of urban infrastructure.

Some people might scoff at this. How could trees possibly be considered equivalent to street lighting or utilities? But trees do a tremendous amount for our communities in a number of essential ways. Unlike a street lamp or a water main, their influence is diffuse – they affect everything from air and water quality, to flooding, to temperatures, to property values and crime – but nonetheless powerful. I won’t go in to their benefits in great detail here; they are well known and documented more thoroughly elsewhere. The important takeaway from Sarah Lonsdale’s article is that urban trees are under more pressure, and facing greater challenges to survival, than ever. And we in the UK are not doing enough to protect them.

According to her research, “Not only have local authority tree maintenance budgets been slashed, but the pressure on councils to remove Tree Preservation Orders (TPOs) has never been higher. Figures from the Planning Inspectorate reveal that the number of appeals against TPOs nearly doubled, from 420 in 2007-08 to 689 in 2011-12. Normally associated with subsidence claims, this dramatic rise in appeals against TPOs has occurred during a phase of cool, damp summers, suggesting that other factors such as planning pressures and back garden grabs are also threatening trees.” Apparently many TPOs are occurring next to high value properties, where the fines associated with removing protected trees are an acceptable sacrifice when compared to the value of the land.

Protection of existing trees is one very important element of preserving our current urban tree canopy. The other is improving development schemes so that they provide yet-to-be-planted trees with the soil they need to thrive and grow in a much more urbanised and dense environment than their predecessors faced.

In the UK, we are very behind on this second point. Trees need large volumes of soil to grow big and healthy. This is established science. And the small plots they receive on a typical city street generally don’t provide enough for them to reach maturity. Urban trees and soils expert James Urban, FASLA, recommends that trees receive at least 28 cubic meters of soil (slightly less if the soil is being shared between two or more trees). In order to grow the kinds of trees we want – ecological workhorses, the kinds of trees we need in an ever-warming world – we must first provide them adequate amounts of soil.

In Canada and North America, cities are starting to address this need by mandating minimum quantities of soil that urban trees receive. Not all of these policies are perfect, but they are a quantum leap forward from planting a tree in a tiny plot and simply praying that it will thrive. The most ambitious policies that I know of are in Ontario, Canada, where several cities – including Toronto – require that all city trees be provided with 30 cubic meters of soil each. A list of all of the soil volume mandates that I know of can be found here.

According to Lonsdale’s piece, a recent Defra-commissioned report (I couldn’t find it on the Defra website, but the Sunday Telegraph did get a look) on urban trees recommends upgrading the status of trees to be considered a form of infrastructure, which I heartily agree with. It also recommends minimum tree planting quantities during the construction of car parks and shopping centres, as well as better maintenance after planning. These are all excellent points. To them, I would add that we must focus not just on the quantity of trees we are planting, but on the quality. And in order to grow quality trees, we must provide them with soil. Our cities and towns have to consider implementing minimum soil volumes for street trees if we are ever to make a better urban canopy – and the healthier, happier, economically vital communities their encourage – a reality.

Steve Chatwin-Grindey is the commercial director of DeepRoot UK. You can find him on Twitter.

One comment

Leave a Reply

Your email address will not be published. Required fields are marked *