G M Moore – University of Melbourne, Burnley College, 500 Yarra Boulevard, RICHMOND, 3121
A recent request to write briefly about the trends affecting Australian arboriculture proved to be a difficult task. In considering a country that is continental, there is great variability – north south, east, west, urban, regional and rural, tropical and temperate (Moore, 2015). Political, economic and environmental values can be different in different States and regions, but from time to time, it is worthwhile taking stock of the things impacting upon arboriculture and where the future might take urban tree management.
The clearing of native vegetation as peri-urban areas of cities and regional centres expand is of major concern in most States, but is more severe in some than others. The character of existing and future suburbs has been changed or threatened by the rapid clearing of trees and there are more subtle changes wrought by the loss of tree canopy cover through intense urban renewal. Such changes put at risk the realisation of the potential for services and functions that urban trees provide and threaten both the economic viability and environmental sustainability of those suburbs. In some new urban development projects, there is no place for trees in private open space and the narrowness of streets often leads to the failure of nature strip tree plantings as vehicles are parked on the only space available. In these places there is very little potential for trees to provide shade or other services for future generations.
As of the middle of 2015, there are many parts of Australia experiencing drought, and there is the prospect of an el Niño event over the coming summer of 2015-6. With a recent history of record high summer temperatures in many parts of Australia, rainfall patterns altering, and cyclonic and major storm events increasing both in frequency and ferocity in all regions of the country, the topic of climate change cannot be far from public attention and the impacts of climate change on arboriculture are already being felt. Trees have been windthrown or experienced major limb failures which have resulted in significant property damage and, sadly, deaths, including those of young children. Arborists are being asked to determine why such failures have occurred and whether tree inspection prior to the failures could have prevented them. This then turns a spotlight upon the training of arborists and on the protocols that are used during tree inspections. The demands for higher levels of arboricultural professionalism and for impartial and independent consultancy advice are greater than ever.
Images of fallen trees on homes and vehicles are dramatic and can lead to a knee-jerk reaction and the removal of large numbers of trees. The countervailing sentiment that the moderating influence of trees on wind speeds during storms has prevented even greater damage or injury rarely gets media exposure. Many major tree failures can be traced back to an aging urban tree population where trees planted a century or more ago are still providing amenity, but have been subjected to a great deal of canopy and root disturbance, both of which can contribute to their failure. While there have been inadequate staggered tree plantings and replacement strategies over the past century to provide a canopy of mixed age classes and greater species diversity, there has been some progress in this regard in some parts of Australia in the last few years with the adoption of urban forest strategies by some local government authorities.
While the value of functions and services that are provided by urban trees are still to be accurately calculated and accepted by both the economic and legal systems, progress is being made (Moore 2015a). Health authorities have recognised the value of shade from the urban forest canopy in reducing the urban heat island (UHI) effect and preventing heat-related illnesses, particularly during heat waves. Heat waves are the greatest killers of people of any natural phenomenon and in a country as warm and dry as Australia, predictions made under climate change scenarios are suggesting that the number of heat-related deaths, hospitalizations and ambulance call-outs will increase substantially, as will the costs to society. Consequently under an economic imperative, health authorities are investigating ways of reducing costs and are promoting an increase in urban tree cover as a possible remedy. At the same time, however, intensive urban and inner city re-development is resulting in a decline in the tree cover in many major Australian Cities and regional centres.
A good tree in a front garden can add $5,000 to domestic property values, and others put the value as high as 5% of the property value, which has been verified by Plant’s (2015) recent work which put the value at 5.4%. (Boyd 2010). Earlier work estimated that a tree-lined nature strip added 30% to properties compared to similar houses on treeless streets just two blocks away (Gonzalez 2007), but people would prefer that the trees were in their street but not in front of their homes (Plant 2015). Survey results showed that 73% of Australians want a backyard and that for 57% of respondents, having a park within a 5-10 minute walk of their home was important to them (Planet Ark, 2014), which is consistent with health authorities finding that the presence of vegetation, and trees in particular, increased both active and passive recreation (Moore 2015). In many cities, the green and leafy suburbs have been subject to multi-unit developments on large blocks full of mature trees, the removal of which ignore the community's valued, local characteristics and diminish property values (Moore 2014).
At a time of rapid, and in some political quarters, controversial change, it is perhaps not surprising that a paradox emerges. On the one hand, there is a drive for tree clearing in many places precipitated by the need for development, better roadways and more dwellings as the Australian population, particularly in urban centres, grows rapidly. On the other, planners and health authorities are recognising the need for greater canopy cover to reduce heat wave related deaths and to encourage healthier lifestyles. These are two major economic drivers affecting arboriculture at present and during a time of rapid change; it is not really possible to predict how things will eventuate. This can only be done with the value of hindsight.
If the full measure of the benefits of the services and functions provided by canopy cover, urban vegetation and vegetated open space are to be captured, cover needs to be established in excess of 30%. Many, and indeed the majority of, Australian local government districts have a cover of 20% or less. It is noteworthy that several local government authorities have established challenging and increased tree cover targets, which would see canopy density double, from lows of around 13% to 20% and from a more common 20% to 40%, over a 20-30 year planning period. The major drivers of these targets are economic and health related, rather than environmental or conservation values. Here lies another conundrum: at the same time as the value of urban trees is increasingly being recognized by some sectors of Australian society, other sectors are removing larger, older trees in increasing numbers.
Its island status has spared Australia of many of the pests and diseases that have affected native and exotic tree species in other parts of the world, but as conditions warm and dry periods extend there has been an increase in tree deaths from biological causes and our small number of pathologists and entomologists are hard-pressed to cope. Rising temperatures are likely to facilitate an increase in both fungal and insect pests and there is a lag phase in the responses of vegetation, and in tree species that lag may be decades or centuries, which makes managing tree populations very difficult. Australia cannot escape the effects of global warming and so much is happening at a time when there have been severe cuts in government spending on science, the environment and climate change.
Myrtle rust has cut a swathe down the east coast of Australia over the past five years, while cypress canker has steadily taken a toll on older, stressed conifers. More older pines have succumbed to the fungus, Diplodia pinea, and more recently there have been outbreaks of the exotic insect, giant pine scale (Smith and Smith 2014). These tree deaths have been particularly noticeable in south eastern Australia, which experienced a 10- 13 year period of below-average rainfall from 1999 until 2010-2, followed by floods and water-logged soils. Such fungal and insect attacks on native and exotic trees have caused significant tree losses, raising concerns about the future role of some species in our urban and regional landscapes.
Australian arborists tend to be earlier adopters of technology and there is little doubt that technology will play an increasing role in urban tree management. Root systems can be mapped non-destructively with ground penetrating radar (GPR) and in some States Avenues of Honour and other significant trees can be located and identified using i-phone Apps. These technologies are still relatively new and it can be expected that their ease of use and accuracy will improve at the same time as their cost. Other technologies using fluorescence allow the ready determination of photosynthetic activity and can be used to estimate tree vitality (Johnstone et al 2013). Soon these approaches will allow the ready assessment of tree condition, soil properties and the identification of pest and disease causing organisms. The proper use of such technology will demand a well- educated and professional arboriculture.
Our urban street trees have proved to be great societal assets. While many specimens have been lost over the past fifty years, many have been saved and preserved through the actions of local citizens who have seen the value of vegetation to future generations. Being on the cusp of significant change, provides opportunities for both the urban forest and the arborists who manage them to in make significant contributions to the sustainability and liveability of cities and regional centres for decades and centuries to come. Carpe diem!
Dr E Moore, linguist, is thanked for reading the manuscript and her helpful suggestions.
- Gonzalez C (2007) Why a tree-lined nature strip can add 30% to you property value, The Sydney Morning Herald, Domain, 9th March 2007.
- Johnstone D M, G M Moore, M Tausz and M Nicolas (2013) The Measurement of Vitality in Landscape Trees, Arboricultural Journal, 35 (1) 18-27.
- Moore G M (2014) Defending and expanding the Urban Forest: Opposing Unnecessary Tree removal requests. Williams G Editor, Proceedings of the Fifteenth National Street Tree Symposium, 70-76. University of Adelaide/Waite Arboretum, Adelaide, ISBN 978-0-646-92686-5.
- Moore G M (2015) The Winds of Change – Climate Change – are Blowing. AREA Newsletter, Arboricultural Research and Education Academy, International Society of Arboriculture, 10 (2), 3-4.
- Moore G M (2015a) The Economic Value of Urban Trees in the Urban Forest as Climate Changes,
- Proceedings of the XXIX International Horticultural Congress on Sustaining Lives, Livelihoods and Landscapes, Sustainable Management in the Urban Forest Symposium (in press).
- Smith D and Smith I (2014) Endemic pests, current threats and future risks to Australian Urban forests. Williams G Editor, Proceedings of the Fifteenth National Street Tree Symposium, 36-48. University of Adelaide/Waite Arboretum, Adelaide, ISBN 978-0-646-92686-5.
- Planet Ark (2014) Valuing Trees: What is Nature Worth, Planet Ark, 47 pages.
- L.J Plant, T Morrison and A. Rambaldi (2015) Street Trees: Paying their Way in Property Value Benefits. Proceedings of the XXIX International Horticultural Congress on Sustaining Lives, Livelihoods and Landscapes, Sustainable Management in the Urban Forest Symposium (in press).