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Sustainable cities need trees, not freeways

Trees provide services to cities that far outstrip their cost. Tim Parkinson/flickr

As we worry about where we will put Australia’s ever-increasing population, urban trees are becoming collateral damage.

So how much are our trees worth to us? According to Melbourne City Council, they can cost up to $62,000 each.

But putting a price in dollars on a city’s trees does not represent their real value.

Without urban woodlands, our future cities will be places where no human would want to live.

People need trees; trees need people

Australia’s cities are well-treed; they are woodlands rather than forests. These urban woodlands have formed as a result of the reciprocal interactions between people and trees.

Trees beguile people into planting them and caring for them, or sneak into places when no-one is looking. Some of them even manage to survive a transition from natural forest to suburbia.

But our relationship with trees is not simple.

People ruthlessly expunge some culturally malodorous trees, while sacrificing themselves for others. This interagency between trees and people means that, if we want more or fewer trees in any parts of our urban areas we need to know how people affect trees and how trees affect people.

We can conclude that trees must affect the urbanites of Australia in a highly positive way, because their density in cities and suburbs has massively increased in the last half century.

In 1961 there were 26 trees per hectare of eastern Australian suburban garden. By 2006, that was up to 85. Street trees have increased from one outside every two gardens to four outside every five gardens. Clearly, we want trees.

When asked, most city people will say that they plant trees because they are beautiful, support wildlife and are good for “the environment”. Hardly anyone mentions the well-established fact that trees provide services that save cities much more than the trees cost.

Urban trees moderate our cities’ environment, and we choose the ones that help us most. Deciduous trees are most favoured in the cities with cold winters and hot summers, providing shade in summer and sun in winter. Evergreen spreading trees with dense crowns are most favoured in the tropics and subtropics, where shade is a good idea in all seasons.

Different tastes are killing our trees

The beauty of trees is almost unanimously celebrated by Australian city dwellers. However, opinion varies considerably on the beauty of any particular tree and on whether we should have trees in gardens.

And of course, our personal attitude to trees is affected by our willingness to garden, capability to garden, fondness for native plants, fondness for home production of food and love of flowers. The trees also have a say, individual species having preferences for particular environments, not always satisfied where they are planted.

Different types of gardens attract different birds, so it may be a good thing for bird diversity that taste in gardens differs so widely within streets. There are many native species that partly depend on the urban woodland for their survival

In Australia, neighbours rarely have similar gardens or the same trees. A change of owner often leads to the felling of one type of tree, to be replaced by another. Most trees that are felled in cities are killed by tree lovers in their gardens for reasons of taste.

It’s wasteful to be constantly felling and replanting trees. Big old trees have been very lucky to survive changes of ownership or to have one owner in place for a very long time. These trees are the ones that give us our sense of place and are some of the most important habitats for other urban sentient beings, like birds and possums.

Perhaps we should be protecting our old trees, diverting water from wasteful industrial uses, encouraging domestic production of vegetables, fruit and nuts and concentrating on developing public transport systems suitable for low density urban areas.

It would make more sense than building freeways that will be useless when, in the near future, oil runs out. Let’s not destroy the beauty, amenity and productivity of our inner and middle suburbs in the process of urban consolidation.

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