Governments at all levels have invested heavily in greening the Australian suburbs. However, in a recent report, we showed that the greening work of most metropolitan local governments is actually going backwards.
This is a problem because greening has obvious environmental and economic benefits. Environmental benefits are obvious and relatively easy to calculate. For private owners, many studies have linked greening to a range of economic benefits such as energy efficiency and high housing prices.
So how do we explain the loss of the green cover?
How do we track changes?
Our research aims to assess the reasons for urban greening and the benefits and losses.
Based on i-Tree, a well-known sampling method for urban vegetation distribution and related land cover, we compare 2016-17 data with early assessments from 2008 to 2013 to examine changes in vegetation cover in local government areas. .
The report shows that there is a large difference in the growth and loss of canopy across the country. However, as communities change over time, the nature of urban vegetation is constantly changing, often explaining losses and benefits.
For example, in a chart highlighting the extent of changes in canopy coverage in metropolitan local governments, Glenorchy, Tasmania, showed the largest loss of tree canopy (more than 15 percentage points) between 2008 and 2015. However, an increase of more than 12% in shrub area largely offsets the loss of the canopy.
Similarly, Armadale in Western Australia received more than 12% of canopy cover between 2011 and 2015, but lost more than 15% of shrub coverage.
Australia’s metropolitan local governments are very diverse in terms of size and land use. The largest of our research is the Queensland Cairns Regional Council, which is 1,500 times the size of the smallest Peppermint Grove area in downtown Perth.
Some local government areas are dominated by non-urban land uses. This means that natural processes such as forest fires, droughts and forest regeneration will have a major impact on greening. Others will be affected by urban intensification and housing growth.
For some local governments, simply using tree loss as a function to understand greening is a problem. Conversely, a more appropriate measure might be the total change in urban greening (canopy, shrubs and turf) during the two studies. These results show that 54 out of 139 local governments (39%) suffered statistically significant losses in total green space.
Increased in Australia’s major metropolitan areas, which is equivalent to 2.6% of vegetation loss in our urban environment. This doesn’t sound like much, but it’s equivalent to 1,586 square kilometers – bigger than Brisbane.
What explains this decline?
The loss of green space in many local government areas exceeds 5%, which provides clues to the type of process that drives this loss. For example, Newcastle, New South Wales, lost 8.5% of its green space during our study, mainly due to grassland cover losses caused by greenfield development.
However, in downtown Ashfield, the padded land for once vegetation continued to grow rapidly, with the conversion from grass to hard surface accounting for the majority of its 7.3% loss of green space.
In some cases, local government areas suffer losses at similar locations. For example, the area with the greatest loss in Perth Greenland is the band that extends from the inland Melville to the coastal East Fremantle. In these places, the traditional Australian backyard is dedicated to densification and filling.
How do our cities compare?
In recent years, interest in these benchmarks has increased internationally. In the United States in 2012, David Nowak and others used the i-Tree method to examine the growth and decline in vegetation coverage in 20 cities. The coverage of trees and shrubs in American cities has changed significantly (54% in Atlanta and 10% in Denver).
The good news is that Greater Melbourne and Adelaide have a tree and shrub coverage of 24%, which is better than the lowest in the US. Hobart’s shrub and tree coverage is as high as 57%, higher than Atlanta.
In Australian cities, variability is evident. Canopy coverage ranges from 77% (Yarra Ranges, Vic) to 3% (Wyndham, Vic).
Urban forests in the United States are also affected by natural forces like Australia. New Orleans lost the largest amount of canopy coverage (10%) because of the damage caused by Hurricane Katrina during the study.
However, historical comparisons are most striking when considering the downward trend in greening. The backyard was once a symbol of the lifestyle enjoyed by generations of Australians who grew up after the Second World War.
If the downward trend in green coverage continues, should the Australian backyard be classified as a threatened species? Https://theconversation.com/were-investing-heavily-in-urban-greening-so-how-are-our-cities-doing-83354