Large trees line Kingsway, a busy road in central London. Copyright Arup.

+ You only have to walk along the tree-lined canals of Amsterdam, the boulevards of Paris or London squares to know that it is the large species trees that help create memorable city environments.

Planting large species trees in urban environments brings a host of social, environmental and economic benefits. So it’s high time we halted their serious decline.

Many of our finest urban trees are a living legacy from the Victorian era and a substantial number are now nearing the end of their lives. The more recent proliferation of smaller ornamental varieties has been a response to a misunderstanding of the problems with trees, and fear of issues like structural damage and subsidence.

With careful planning and advances in planting technology, our towns and cities can easily accommodate more large trees. In the context of climate change, the importance of protecting and planting new stock in urban areas has never been more critical, and this is a notion that is emphasised by numerous recent UK Government reports and initiatives.

Whilst all trees are beneficial to an urban environment it is the larger species (i.e. trees that can attain heights of over 15m) that are the particularly significant elements that can match and compliment the architecture of the city in scale and create great city places. You only have to walk along the tree-lined canals of Amsterdam, the boulevards of Paris, lime allées of Berlin or London squares to know that it is the large species trees that help create memorable city environments.

A report written by Arup’s landscape architects for the Construction Industry Research and Information Association (CIRIA) showed that the annual net benefit of planting large species trees is 92% greater than for small species trees. In fact, the net benefits are so great that large trees pay for themselves within five years. The growing body of research referenced in the guide provide a convincing argument that it makes sound financial sense to plant larger species trees.

The financial benefits of trees range from increasing property prices to reducing energy consumption by regulating local microclimates. They’ve also been shown to improve physical and mental health, reduce hospital recovery times and increase workplace productivity. Their canopies intercept rainwater, reducing run-off and flood risk. And their roots filter water, improving its quality.

Cities are beginning to recognise and measure the value of their existing large species trees. The New York City Parks Department determined that the 600,000 street trees in its five boroughs provide an annual benefit of $122m — more than five times the cost of maintaining them. A similar exercise is planned in London for the end of 2012.

The evidence shows that large species trees are key to creating climate-proof, happy and healthy cities for the future. So why aren’t we planting more large trees instead of the small ‘lollipop’ species you see being planted along city streets?

Part of the problem is the myth that big trees cause issues like subsidence and structural damage. This might have been true in the past, but modern horticultural techniques mean that with careful planning it is easily possible to plant large species trees in a well-prepared urban environment without problems.

It is vital that large species trees are seen as part of an integrated urban ecosystem, rather than being considered merely as ornamentation. Trees are a vital component of the Green Infrastructure in our urban areas.  If we don’t make the most of these techniques and plant more large trees, we’ll be short-changing future generations and miss a huge opportunity to climate proof our towns and cities.