Page 4360 - Week 12 - Wednesday, 25 October 2017
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In summer localised temperature differences can be over 12°C between pavements in sun or shade.
For someone walking around, 12 degrees makes a huge difference. And, of course, a 12-degree difference between a shaded roof and an unshaded roof makes a huge difference to comfort within a house.
Of course trees are not just loved for their cooling impact; in many suburbs trees are an important part about what people love about their local neighbourhoods. In older suburbs at this time of the year the exotic trees put out their new leaves and all of a sudden the local landscape is filled with the light green of fresh spring leaves. For many years I lived in Downer, and one of the joys of living there was the big old claret ashes in my street. One of the sad things has been the death in the past few years of many of these trees, partly through old age but, importantly, partly through drought.
In suburbs built more recently more native trees have been planted, which provide better benefits for our local wildlife. Native trees in streets and parks can provide a corridor for bird species to move from one nature reserve to another, which is important for our biodiversity. I know that quite a few people have planted native trees and shrubs in their gardens to attract birds and bees and other parts of our biodiversity. All of these benefits add up to measurable economic value. International research has shown that urban trees have a financial benefit in the order of tens of thousands of dollars through lower cooling bills and higher property values. Ideally, we would get precise local values for this, and I am sure they would be similarly large.
While many suburbs of Canberra have great tree canopies, some do not. For example, there are places where the street trees chosen have proved not to be successful and the street trees do not provide a good canopy cover. There are also many gaps in suburbs built from the 1990s onwards. During this time there has been a change in the approach of design for suburbs. Streets were narrowed with less room for trees. Block sizes were reduced, but at the same time the size of new houses got bigger.
The results of these changes has been that in some suburbs there is no room for large canopy trees in peoples’ yards. There is also no room for large canopy trees in the street. People who live in these suburbs do not get the same benefits of trees as those in older leafy suburbs, and the biodiversity benefits I talked about do not occur either. However, tree canopies in older suburbs are also under threat.
Many older suburbs, like Curtin and Garran, are seeing rapid redevelopment. These suburbs traditionally had blocks from 700 square metres up to 1,400 square metres and smaller houses of between 100 and 200 square metres. This left room for many large canopy trees. Now both multi-unit developments and McMansions are replacing the small existing dwellings, with the garden space that remains being a strip around the outside of the building. This sees the loss of almost all existing vegetation and leaves very little new room for canopy tree plantings.
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