It's not rocket science!

Nearly 70 people, including a splash of mayoral candidates of various hues, participated in the second of Bristol’s biannual TreeForum talks. Silole Menezes of world renowned ARUP gave us a glimpse of best practice in urban greening.

I appreciate it now, best practice requires a sustainable urban water supply; you see a few hundred years ago the natural process of rainfall and infiltration into the soil was enough for a 100% canopy cover of vegetation. But humans have filled cities with concrete, tarmacand roofing. Now most rain runs off into drains picking up pollution on the way. Our water companies and agencies have to manage the resultant flooding and pollution, plus they need to provide clean water to us, the inhabitants, and sometimes for the trees and parks too. This “water system” will cost more in the future and in some places is unsustainable, therefore cities including Bristol need to be retrofitted with “interventions” to capture or delay some of this rain water, at least enough for the 30% or so canopy cover we need for our health and wellbeing. 

Silole also facilitated a lively discussion. How is this done? It takes vision and planning on a large scale, starting with the hills surrounding a city to fit water holdups like reed beds, streams, ponds, parks, woods, trees, planting, gardens, tree canopy over car parks, green roofs and allotments . Each of these interventions delays and filters the water after it falls from the skies (something we have witnessed quite a lot recently). This prevents localised flooding and low level pollution getting into the water system. The green infrastructure itself can then provide the benefits to city dwellers without the need for expensive piped in water. This is being done across the world and as close to home as Grangetown in Cardiff and Sedgemoor in Somerset.

Pocket scale green intervention

We know the costs, but how can we value the benefits? It’s not easy, but DEFRA have a project team working on applying social return on investment economics to this sort of thing and the Bristol TreeForum are working with them.

Isn’t this all too big a scale to manage? Well we will have a mayor soon who may wish to commence a sustainable vision for the city, he or she won’t have any shortage of help,indeed one TreeForum member is doing research into this now as his PhD at Bristol University. But what can we do at the local level? The big picture is just too vast for any one architect or enthusiast to handle but planting street trees, greening parks and car parks, planting on roofs and pocket habitats are all small interventions possible by anyone of us.

So don’t concrete over your front garden or chop down your trees, that is the wrong direction, this is not rocket science but if you plant some not only will it be tasty but you will be doing the right thing!

The second part of the evening was an introduction about the Bristol Core Strategy; the top level document governing all new development and building work. Adopted in June 2011, it has a number of new clauses relating to trees. These are in BCS9 and the TreeForum looks at every full application in Bristol if trees are or could be involved to check compliance. 

BCS9 has three relevant sections: If the development is next to a green corridor then landscaping must enhance it. Secondly, if there are existing trees, plans must retain them wherever possible especially if the trees offer landscape, amenity or nature benefits. If they must be felled then there are some quite onerous planting obligations to ensure canopy cover is rebuilt quickly. Finally, paragraph three deals with the opportunities to increase planting e.g. in a car park and we are will objectif that isn’t complied with. The Council Planning Officer confirmed (thankfully) that the TreeForum is interpreting this all correctly, so it is down to architects to read the clauses and ensure they are fulfilled.

The Bristol TreeForum was set up four years ago by the Council to engage with the local community and help increase the city’s tree coverage. Its current chair is Clive Stevens, local resident, business man and volunteer (like all other members). Its purpose is to persuade and influence landowners in Bristol to increase the city’s tree canopy cover. For this we need to involve more people.  Clive says;”We live in a democracy, so we will only achieve these health benefits by cajoling our councillors, mayor and MPs into making sure trees are better protected and more get planted. We need a significant part of Bristol’s populace to support this goal. We are a catalyst and conduit to help people make Bristol a better place to live in. Just get in touch, it’s free, you don’t even have to come to our meetings, you just have to care about our and our children’s future.”

Article by Clive Stevens; [email protected] for further information. And thanks to Silole Menezes and Carl McClure.

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