Arboricultural strategies for managing the urban forest in a time of climate change

The impacts of climate change on urban forests will not be uniform on either a national or global scale, making decisions related to planning and managing urban forests difficult. Climate change is likely to hit some parts of Australia hard, primarily through reductions in rainfall and increases in atmospheric carbon dioxide and temperature. The urban forest is likely to be impacted in several ways, the most apparent of which will be the direct effects of higher day and night temperatures on the trees of the urban forest and their associated biota as well as reduced water availability. Water is a valuable resource, but its scarcity for the urban forest is often due to its preferred use by society for other, higher priorities. However, the value of the urban forest in providing environmental and ecological services that have significant benefits for human health, well-being and the liveability of cities can be used by urban tree managers to argue for a higher priority of water use by the urban forest, especially if urban tree managers use their knowledge of tree root systems and their interaction with soils to maximize the efficient and effective use of water. Understanding stomatal behaviour allows optimal timing of irrigation for photosynthetic efficiency while capturing the benefits of transpirational cooling which may reduce excess deaths during heat waves. Many commonly planted urban trees have wide temperature and water tolerance ranges and for some genera there are ecological displacement series where, as temperatures warm and rainfall decreases, one species within the genus is replaced by another. This provides urban foresters with a wide pallette of species with which to plan and plant cities. There is much that arborists and horticulturists can do to mitigate some of the consequences of climate change if they act on a city-wide or regional scale. A sound knowledge of trees biology, ecology and physiology can be used to develop arboricultural strategies for managing the urban forest and formulating decision making matrices at a time of climate change.