Canberra is pretty green. Its architects were influenced by garden cities, and they included lots of greenery and parks in their designs – so much so that it’s affectionately known as the ‘bush capital’. (Admittedly, part of that name might be because it is inland.) Today, the city has more than 750,000 urban trees; with a population of around 400,000, that’s almost two trees per person. Not so much a loose collection of trees, but an urban forest.
Canberra’s trees, and where they came from
Technically, many of them come from the charmingly named Yarralumla Nursery, after the indigenous Australian name for the area. But Canberra’s lands were originally eucalyptus woodlands and forests. It’s still near mountains (well, small mountains) and nature reserves, and tree planting has been a feature of its development from the beginning. Its urban forest is a great example of the full range of benefits that we get from trees – not just city trees, but all trees.
Canberra: not just a loose collection of trees, but an urban forest.
(Incidentally, it seems that some Canberrans love their trees so much that they commemorated them with crosses when they were cut down because of disease.)
The urban forest, and what it can do
Lots of things. Trees can:
- moderate climate extremes, including the infamous urban heat island effect
- cool shaded areas
- trap and remove air pollution, improving air quality
- capture, intercept, and filter rain, decreasing runoff and water pollution
- create green space for relaxation and recreation
- and not least, make the city beautiful!
Many of these have financial benefits. Cooler, shaded areas need less air conditioning – sometimes as much as 30% less – which saves electricity. Less polluted water means less need for expensive water treatment plants. And better flood control means, well, less flooding, and less need for flood control systems. Larger trees are often more effective at all of these too. Since leaves attract and absorb pollutant particles, water droplets, and so on, larger leaves and branches can intercept more water and pollution, and they also cast more shade.
Cooler, shaded areas need less air conditioning – up to 30% less.
And that’s not even counting the relaxation and public health benefits of having green space. Mental health improves, and we are less stressed when we have green space. And people even report feeling healthier when they have more trees around. (Hello, cultural ecosystem services!)
Exactly how much is this worth in cash? It’s hard to calculate cultural services, so just remember that all the numbers would be much higher if they were included. But energy, pollution, and water flow control savings can be calculated per unit of tree crown area. Then they can be matched with maps of the urban forest that show tree cover, and because cover changes a little every year, a five year average is a little more accurate. And for 400,000 trees, it’s US $4 million, or $10 per tree.