Arboriculture & Urban Forestry 39(3): May 2013 tic approach to urban water management the integrity of urban greenspaces can not only be maintained, but can be enhanced in a manner that improves social amenity and economic efficiency. OVERVIEW OF ADELAIDE Adelaide, the capital city of South Australia, and its metropol- itan environs, is the 80 km long, 30 km wide urban capital of the driest state on Earth’s driest inhabited continent. Despite low rainfall levels and high summer temperatures, Adelaide maintains a higher density of urban trees than many of its Australian capital city counterparts (Kirkpatrick et al. 2011). During most of the last decade, the entire southeastern region of Australia was subjected to a PDP, the result of which included severe water restrictions for Adelaide’s private and public gar- dens. Emerging from this experience are first-hand lessons about the costs associated with stressed landscapes, dead tree removal and the loss of environmental services from the urban forest. The drought also highlights how policy reductionism and cost-center accounting create greater potential for institutional conflicts. Empirical evidence has long demonstrated that urban forests provide multiple benefits that go far beyond adding aesthetic beauty to neighborhoods. Trees in parks, streets, and yards conserve energy in buildings, improve air quality, re- duce storm run-off, and enhance the beauty of communities by adding color, texture, and form to community landscapes (e.g., Dwyer et al. 1992; McPherson et al. 1998; McPherson et al. 1999; Brack 2002; Killicoat et. al. 2002; McPherson and Simpson 2002; Nowak and Dwyer 2007). Additionally, Tar- ran (2009a) summarizes numerous studies that document the beneficial human health outcomes attributed to urban forests. Policy failures and the complexities of managing urban forests are also well recognized, if not yet well understood, addressed, and resolved. Developing effective urban forestry strategies and policies involves an array of difficult choices. Some choices result in inefficient resource use because many essential benefits and services of urban trees, such as aesthetic values, watershed protection, and climate regulation, are not priced. These benefits and services are valued differently by different households within the same neighborhoods and across different communities. These values and interests in the urban forest and the resources they provide may differ greatly and have a tendency to shift over time, for example, during a PDP. As policy interests shift and community expectations conflict, difficult management challenges are created that require innova- tive, science-informed strategies to better integrate urban trees into community development efforts and balance economic, social, and environmental needs with local interests. The emerg- ing views of what urban trees are and what they contribute requires local governments to search for pragmatic management strategies that deal coherently with the contributions of trees to urban development. Additionally, governments must search for organizational structures that better use of these contributions. These issues are especially relevant for Adelaide because the city’s history and identity are associated with its public space, parks, and gardens. The ‘parkland town’ is a distinctive feature of the urban scene throughout Australia. Its main elements are a central core of town-lands for business and commerce with a sur- rounding belt of parklands reserved for public use and a periph- eral zone of suburban lands. Williams (1966) described the park- land concept with these three elements, explaining “the whole 103 served by a pattern of roads radiating from the center. This three- fold division had its first and greatest expression in Adelaide.” Over time, Adelaide’s provision of public open space, streets, generous-sized and housing allotments resulted in house- hold blocks with a mix of fruit trees, native plants, and exotic ornamentals, providing canopies that filled in the linear ma- trix provided by street trees. Today, viewed from an elevated vantage point, the suburban sprawl is lost beneath a canopy, high-rise buildings appearing to be dotted throughout a forest. Climate and Trees in Adelaide Adelaide is situated on the St. Vincent Gulf in central, south- ern Australia and has a hot Mediterranean climate (Koppen climate classification Csa; Peel et al. 2007), meaning mild, wet winters and hot, dry summers. Of all the Australian capital cities, Adelaide is the driest. Rainfall is unreliable, light, and infrequent throughout summer. The average monthly rainfall in January and February, according to data collected for more than 150 years, is around 20 mm, but completely rainless months are not uncommon. In contrast, the winter has fairly reliable rainfall with June being the wettest month of the year, aver- aging around 80 mm. The annual estimated average rainfall for Adelaide is 585 mm. Annual rainfall totals have ranged from a high of 882.4 mm to 257 mm. In the summer, the average maximum temperature is 29°C, with around three days a year when the daytime temperature is 40°C or warmer (Na- tional Climate Centre 2009; Australian Government 2011). Awareness of the climatological conditions experienced on the Adelaide plains during the PDP is essential to the scientific understanding of the response of the urban forest. The Government declaration that the city was experiencing drought is of interest since evidence suggests it was declared because of a water supply shortfall (Gómez-Muñoz et al. 2010) rather than a lack of precipitation (Australian Government 2011). While a consistent lack of precipitation throughout the water catchments over the time under discussion led to the drought declaration, precipitation on the city and its metro- politan environs was either average or above average for three of the ten years, and during the summer period (i.e., the time of greatest stress for the urban forest) of two others, there was higher than average summer rainfall. From March 3, 2008, Adelaide recorded 15 consecutive days of tempera- tures more than 35°C, again a record for an Australian capital. In November 2009, another heat wave occurred. Daily maximum temperatures during the heat wave were rough- ly 10°C above average in many locations. From late Octo- ber until mid-November, the city experienced 10 consecu- tive days with maximum temperatures greater than 30°C, six consecutive days over 38°C, and the highest November temperature ever recorded, 43°C, on November 19, 2009. Both heat waves were unusual since the highest tempera- tures are usually recorded in January and February. Since, locally, these heat waves generally correspond to periods of no precipitation, substantial stress was placed upon the city’s urban flora. The combination of high temperatures with the lack of available moisture in the soil profile highlights the stresses to which the urban forest was subjected during pro- longed dry periods (Correy 1992; McPherson et. al. 1999; McPherson and Simpson 2003; Gómez-Muñoz et al. 2010). ©2013 International Society of Arboriculture
May 2013
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
