Inspire : Public Works Mar Apr 2013
45 ‘urban heat island’ effect. Furthermore, the shade can provide improved public health benefts by reducing exposure to UV light and associated incidences of skin cancers – as well as increased walking and cycling along tree-shaded paths. Trees can also reduce the cost of constructing and maintaining stormwater infrastructure. By having a tree canopy to intercept rain, there is less incidence of stormwater r unoff and an increased infltration to groundwater. There are also increased biodiversity and wildlife habitat values. Finally, urban trees improve the emotional health and sense of well being in the community, as a result of the aesthetic values, together with increased value of properties in areas with signifcant tree cover. TREATING TREES AS ASSETS Taking an asset management approach to urban trees can result in a number of benefts for councils and infrastructure organisations. Asset managers can optimise the costs and benefts in a strategic way and then demonstrate the return on investment. They can therefore build a wider understanding of and support for the value of trees within the organisation. Furthermore, by using best practice to articulate the need for resources, councillors and other decision makers can understand that they are voting for a resource allocation with a known quantity and value. There is a range of methods for estimating the value of urban trees, each with a different perspective on defning value. The valuation methods include considering the replacement costs only to a holistic approach that captures both the str uctural (intrinsic) values and functional (use) values associated with the social and environmental benefts of trees. The availability of new tools to evaluate the full range of benefts now allows them to be valued and incorporated as a discrete category of urban infrastructure within asset management systems. The most widely used tree valuation methods include: • Depreciated replacement cost (DRC), which determines the value of trees on the basis of their removal and replacement cost; • Helliwell, which is based on a number of factors, such as location, size, conditions, form, etc. which are given numerical values and multiplied by an CONTINUE THE CONVERSATION Have your say on this story. Go to http://goo.gl/jmnxf to comment on this article. indexed baseline monetary fgure; • The capital asset value amenity trees (CAVAT) method, which is based on replacement costs as well as the community value of the tree that is determined by use of a community tree index that considers the number of people that interact with the trees as well as the crown size of the tree; and • i-Tree Eco, is a software program developed by the USDA Forest Ser vice, which accounts for both the structural value of the trees (based on replacement costs) and the value of the environmental benefts that trees deliver, such as carbon sequestration and storage, air pollution interception and removal and stor mwater quality improvements. IN PRACTICE The City of Sydney currently applies the DRC method, basing it on average costs of $2000 to remove a mature tree and $1000 to plant a replacement tree that typically has a root ball of 200 litres. By applying an average value of $3000 per tree to the 30,000 urban trees throughout the City of Sydney, the cur rent asset value would be in the order of $90 million. However, this fgure does not capture any of the environmental, energy or public health benefts associated with the urban trees. Newcastle City Council has recorded 90,000 street trees with another 19,000 trees growing in parks. A study conducted by Adelaide University in 2006 estimated the value of annual net benefts from these trees to be $11 million per year. The City of Melbour ne has valued its 60,000 trees at $650 million, using the Burnley Method of determining the amenity value of trees. In London, the Victorian Business Improvement District has applied the CAVAT method to estimate the value of their 1225 trees as £27 million, which equates to an average of £22,000 per tree. Nevertheless, having these tools and methods is one thing, applying them effectively is another entirely. This will require a multi-disciplinary approach, involving asset managers, engineers, parks managers, landscape architects, arborists and others. Professional organisations, such as IPWEA, AILA and Arboriculture Australia, can play a key role in encouraging and facilitating collaboration between the various disciplines to effectively manage urban trees as a growing asset. ••• Decision- making in relation to urban trees can now be based on costs and bene ts that allow them to be aligned with overall asset management objectives.
Public Works Jan Feb 2013
Public Works May Jun 2013