CLIMATE CHANGE THREATENS URBAN TREE POPULATIONS

The City of Melbourne and The University of Melbourne have released The Future Urban Forest report which finds that 35 percent of all trees planted within the city’s parks and urban forests, and 48 percent of all species of trees planted were either moderately or extremely vulnerable to climate change. The study shows the trees are vulnerable within a moderate scenario under which temperatures are presumed to increase by 0.8 percent between now and 2040.

Species that were particularly vulnerable are those that derive from colder or narrow climates in northern Europe or the north-eastern United States such as the Dutch Elm, the report said. Other species listed as vulnerable were those from narrow climates, such as many locally indigenous and other natives including many of the Eucalypt and Acacia species.

By contrast, the trees which have been identified as suitable for Melbourne’s climate include the sub-tropical South American Jacaranda (Jacaranda mimosifolia), the Australian native evergreen Brush Box (Lophostemon confertus) and the indigenous Coast Banksia (Banksia integrifolia).

The report also states that the vulnerability of the two aforementioned groups presents a particular challenge as both groups were critical to the city from the viewpoint of biodiversity, livability and cultural identity. Whilst these species are forecast to become less reliable in the future, the report finds that they may remain viable in places with suitable management irrigation strategies and improved soil conditions. The implementation of Climate Change management strategies to combat the vulnerabilities in tree populations comes highly recommended. In addition, the report finds that more activity will likely be required in areas such as tree removal, pruning and planting in response to damage, decline and mortality.

While hundreds of species were earmarked as potentially suitable for planting instead of the vulnerable species marker, the report suggests that this area presents further challenges as extra processes will need to be developed to test and select species to determine their suitability. To limit the risk of unsuccessful plantings within larger streetscapes, formal street tree trials will initially need to be limited to smaller areas, it adds.

Liaison with the nursery industry in purchasing plants of the future will also be essential, as will testing any new species for weediness. Finally, the report highlights how it is critical to maintain or enhance diversity when undergoing tree selections in order to provide a healthy urban forest.

Melbourne Lord Mayor Robert Doyle has said the research will be utilised to make evidence-based decisions about which trees should be planted in order to safeguard the city’s urban forest future. “Trees are a defining part of Melbourne but they are also vulnerable to the effects of climate change,” Doyle said. “Past experience of drought, including the Black Saturday period in 2009, has shown us that we need to plant new Australian and international species that are suited to warmer temperatures.”

The Future Urban Forest report comes as the City of Melbourne continues its urban forestation strategy which is designed to increase tree cover from almost 25 percent now to 40 percent by 2040. There are currently around 77,000 trees on Melbourne’s streets, parks and urban forests, and the city is planting over 3,000 trees per year at a cost of $1.5 million.