Confrontation between Sheffield residents and Sheffield City Council over the fate of 11 Lime trees on Rustling Road brought street trees to the attention of the national press. At Landmark we place a high value on the contribution that street trees make to green infrastructure, and not simply because of their amenity value. Urban trees contribute many benefits to the built environment and it is worth considering how to best balance delivery of development, infrastructure, and public safety with the continued function of a key component of the cityscape.
As concerns grow about the quality of the urban environment in towns and cities throughout the world, the importance of protecting and expanding urban forests can only increase. Trees make people happier. This is something we intrinsically understand, from walking down a leafy urban street and exploring quiet woodland, but there is also a wide range of academic evidence to support this statement. Since studies completed by Ulrich in the 1940s, showing hospital patients recovered faster in rooms with views of trees, the medical evidence for the value of street trees has grown. As well as overall wellbeing, the evidence points to the health benefits of living in areas with abundant street trees range ranging from lower instances of skin cancer to improved mental health.
Street trees also help to make streets safer for pedestrians, by increasing caution in drivers and reducing traffic speed. Their contribution to the attractiveness of the urban environment plays a part in the creation of civic pride and a sense of community. On the whole you are likely to be better off, in terms of health and wellbeing, if you are living where trees are a part of your daily environment.
This health value is reflected in property values and, again, there is plenty of evidence of this. The removal of street trees adjacent to homes can result in a 5% decrease in property value, (Wolf, K.L. (2007). ‘City Trees and Property Values’. Arborist News 16, 4: 34-36). In the city of Portland, Oregon the extensive tree planting scheme has increased property value to the extent that the city authority is $13 million better off a year from property tax revenues alone. This sum covers the cost of tree maintenance with a healthy $8.4 million to spare. Further financial benefits of street trees include saving energy, with street trees acting as wind breaks, insulating against heat loss in winter and cooling buildings in the summer.
Where street trees really prove their worth, however, is in environmental benefits. They reduce pollution by removing nitrogen oxide and particulate matter from the air, prevent soil erosion, strengthen wildlife corridors and reduce the urban heat island effect. In cities such as Bristol, with urban waterways, they reduce flood risk and lower water temperature, making urban rivers better places for aquatic wildlife.
Despite the considerable social, economic and environmental benefits which street trees provide, they face a wide range of threats which are already eroding both the existing stock and planting of new stock.
Trees are widely understood to be a potential solution to mitigate the effects of climate change, but changes in temperature and weather conditions are already having an adverse effect on native British species. The Forestry Commission’s 2007 report on climate change found that Beech (Fagus sylvactica) could die out in its current range (within the south of England) by 2050. As the mean temperature increases, drought will increase tree species susceptibility to pests and diseases. Warmer winters will enable pests to survive over winter and exotic pests could potentially spread to the UK, to which native trees will have no tolerance. Drier summers will have a particularly negative effect on the lifespan of street trees.
These are the medium to long term implications of climate change. More urgently, financial pressures are already promoting loss of street trees, as local council budgets can no longer stretch to essential tree maintenance budgets. City trees have to be maintained, like any other infrastructure, over their entire lifetime. Street trees are also at particular risk from felling due to subsidence related insurance claims.
Design and management in the future
One of the many things that we can thank the Victorians for is planting much of the UK’s heritage of street trees. Trees age, however, and those which were planted in the late 19th and 20th centuries are now coming to the end of their life cycle. The limited diversity of species within our cities also poses challenges and, to counter the threat of climate change and climbing temperatures, we will need to consider shifting the range of species that we work with. British native species support more wildlife than foreign species, and as a result we favour them when selecting stock for new development. As conditions change, however, we may need to begin specifying ‘new native’ species from more southern areas of continental Europe which will survive better in our changing climate. Finding those with the right balance to support native wildlife will pose a challenge.
At a strategic level we also need to select species with capacity to resist new pests and diseases. Claims have been made that had the movement of plants within the EU received greater scrutiny, Ash Dieback might have not had the devastating effect it has had here in the UK. If we want to protect our native species and ensure they remain a part of our townscapes and wider landscapes, we must ensure that safeguarding measures are in place, and rigorously implemented, to prevent the spread of diseases and pest from abroad.
We are extremely fortunate in the environmental, social and economic resource that we have in Britain’s street trees. At Landmark we are further fortunate to work with clients who understand the benefits of green infrastructure and actively work with us to plant trees within urban areas. We are developing new skills to face both the environmental and economic challenges to urban development and green infrastructure and ensure that future generations will benefit from cities filled with trees.
For more information please contact:
Morag Macgregor Morag.MacGregor@thelandmarkpractice.com or
Andy Spargo Andy.Spargo@thelandmarkpractice.com