Arboriculture & Urban Forestry 39(3): May 2013 Arboriculture & Urban Forestry 2013. 39(3): 109-115 109 Adaptations of Australian Tree Species Relevant to Water Scarcity in the Urban Forest G.M. Moore Abstract. Water is a valuable resource, but its preferred use by society for other, higher priorities has resulted in a scarcity for the urban for- est. 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 demands the reconsideration of the priority of water use by the urban forest. Health authorities are advocat- ing the value of urban greenspace that may require the use of water, especially storm water, as climate change threatens more severe heatwaves. Trees have an important and long-term role in water-sensitive urban design that efficiently uses and reduces pollution from storm water. Knowledge of tree root systems and their interaction with soils means that irrigation can be targeted in a way that maximizes the efficient and effective use of water. Un- derstanding stomatal behavior also allows optimal timing of irrigation for photosynthetic efficiency while capturing the benefits of transpirational cool- ing, which may reduce extra deaths during heat waves. The economic, social, and health benefits justify the efficient and effective use of valuable water. Key Words. Australia; Drought; Foliage; Root Adaptation; Urban Water Use. Recently, much of the east coast of Australia was gripped with a prolonged period of lower than average rainfall. The State of Vic- toria had entered its fourteenth consecutive year of below-average rainfall (Bureau of Meteorology 2011). Since then, there has been record rainfall and flooding in much of the region, and the media have reported the general relief that the drought had finally broken. The dry period may have been a drought and part of natu- ral cycles of perhaps five hundred years or more, but cur- rent meteorological data are too recent to reveal such patterns. However, the dry period, recent major storm events, changes in rainfall patterns, and summer flooding are con- sistent with predictions made over the past two decades in relation to climate change. It is too early to trumpet the end of the dry period—one season of above-average rainfall should not obliterate the trend of the previous fourteen years. So the focus on water scarcity, availability, and the ef- ficiency of water use in the urban forest is timely and of great urgency in the context of the Australian environment and climate change more generally. However, is there really a scarcity of water for the urban forest? In cities as diverse as Melbourne, Victoria, and Perth, Western Australia, Austra- lia, only about 8%–9% of the available potable water is used for general open space purposes. This includes both public and private (back and front gardens) open space, and even less water is allocated to trees in the urban forest (Victorian Department of Sustainability and Environment 2006; Victo- rian Department of Sustainability and Environment 2007). Furthermore, 10 years ago, gardens, parks, and sporting ovals consumed about 12% of the State of Victoria’s water. Now it is less than 9%. This is a 25% reduction, and the Law of Diminishing Returns suggests that having made significant sav- ings in water, no matter how much one tries, they are unlikely to get more significant savings from parks, gardens, and the urban forest (Water Resources Strategy Committee 2002; Vic- torian Department of Sustainability and Environment 2004; Victorian Department of Sustainability and Environment 2007). Water is a precious commodity, but it is only scarce because other priorities for its use are seen as being more important than open space and the urban forest. No one would deny that the first priority for potable water is to meet the drinking and health needs of citizens. However, in every State, the greatest users of water by far rest in industry and agriculture (Victorian Department of Sustainability and Environment 2004; Victorian Department of Sustainability and Environment 2007). No one would suggest that the urban forest should be irrigated at the expense of drinking water or at a cost to human health or life. The issue is about using a valuable resource sustainably and ef- fectively to capture maximum benefits, including environmental benefits (Nowak et al. 2010). Research must inform the manage- ment practices that are required to maintain the urban forest, using water effectively, efficiently, economically, and sustainably. THE PRIORITY FOR WATER AND THE URBAN FOREST While urban forests are beautiful and decorative, these attri- butes often conceal the many functions and services that they provide to cities to the point where their social, health, eco- nomic, and environmental benefits are overlooked (McPher- son 2007; Moore 2009; Nowak et al. 2010). What else de- livers so many benefits immediately, and benefits that last centuries into the future, prolonging healthy lives and making cities both sustainable and liveable? Urban forests have been ©2013 International Society of Arboriculture
May 2013
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