They provide islands of natural ecology for birds, insects and other animals, as well as filtering the air, moderating water flows, providing street level shade, screening road noise and also reducing the urban heat island effect caused by the thermal properties of buildings and hard surfaces.
In addition, of course, they look nice, which is not a trivial issue, both due to the significant effect mature trees can have on property prices in an area of a city, but also in the promotion of general health and wellbeing. American sociobiologist Edward Wilson argues that the people are attracted to natural environments and feel happier in the presence of nature.
The presence of urban trees also have a number of more unexpected beneficial effects – average traffic speeds are lower along tree lined roads and less ‘road rage’ is also known to occur, tree dense areas typically have a greater sense of community and are often safer as a result.
There are many charities and groups promoting the beneficial effects of urban trees, and running various planting schemes; including Trees for Cities and the Government backed Big Tree Plant scheme in the UK.
Photo from The Seafarer via Flickr