A case for Trees

As Australia breaks record heat for the first month of summer, our research into the value of trees in the urban and suburban context couldn’t be more pertinent. Trees are the greatest urban design tool to connect communities, green our cities and tackle climate change. What other city ingredient naturally cools our city, cleans our air and water, creates homes for native fauna and fosters sociable walkable communities?

TCL consistently advocates for better tree infrastructure in Australia’s emerging communities and to ensure the residents in these growth areas reap the benefits of a shady, cool and beautiful tree canopy. “The Case for Trees” research was originally founded in TCL’s masterplanning for Lovely Banks, Geelong – we created the booklet as a tangible tool to quantify the value of greening our cities and equip decision makers with hard evidence to enable the planning and implementation of greener suburbs.

The merits of trees in our city centres and established parklands have long been valued and recognised. Not only for their amenity value, but more recently, for their important role in cooling our cities. Many cities and councils are recognising the value of trees in our more established urban environments through the establishment of canopy coverage targets and urban forest strategies to improve the long-term health of our communities.

Yet in the growth suburbs of Australia’s peri-urban areas, where large scale suburban development is transforming farmlands into our newest communities, the value of trees and their many benefits is mostly ignored. New streets in typical conventional developments are not providing the conditions for trees to be large, healthy or thrive. Councils, state government agencies and service authorities are planning, mandating and approving streets with narrow verges, shallow soils, little access to water, poor drainage and uncoordinated services. Trees and their important horticultural needs are not part of a considered and coordinated street and subdivision design consideration.

Environmental benefits

Trees enrich the environment of developing and established communities.  In urban and suburban contexts well planned tree canopy coverage significantly reduces local temperatures and the urban heat island effect.  Trees are also able to improve the air quality of local communities through filtration of pollutants and sequestering carbon and producing oxygen. Tree roots absorb stormwater reducing the amount of Nitrogen, Phosphorus and heavy Metals entering our drainage systems.

Trees reduce temperatures and costs

Cities are increasingly vulnerable to rising temperatures through climate change and urban heat island effects. The ability of trees to provide localized cooling for urban communities is well documented. They do this in two simple ways, transpiration, the release of moisture to the air through leaves and the provision of shade via canopies. Temperature reductions under canopies are significant, ranging from 5-20°C cooler (Greater City of Geelong Urban Forest Strategy 2015 – 2025).

The shade provided by established trees, mitigates and moderates temperatures by cooling buildings during the warmer seasons and protects buildings from the cold and wind during the cooler seasons. Increasing tree canopy coverage by 10% over buildings reduces annual cooling and heating costs by 12-15%.  (City of Melbourne. Urban forest strategy, making a great city greener 2012-2032). 

Trees improve air quality

Trees are a significant urban infrastructure asset and are increasingly considered a key strategy in mitigating carbon emissions and pollutants within the atmosphere. They also improve air quality through their ability to filter chemicals and pollutants.

Mature trees are 60-70 times more effective in reducing air pollution in comparison to smaller trees (Moore, 2009 Urban Trees: More than what they cost). Automobile exhaust is a major contributor to these pollutants, with trees located near roads, able to absorb nine times the amount of pollutants in comparison to more distant trees.  (Burden, D. 22 Benefits of Urban Street Trees).

Trees reduce stormwater runoff

Urbanisation has led to a rise in impervious surfaces, increasing pollutants levels, stormwater runoff volumes and peak flow rates within environments, increasing the risk of localised flash flooding.  Substantial tree plantings provide a simple solution to reducing the associated problems of stormwater runoff, as canopy and root systems of trees prove to function as incredibly effective natural drainage systems.  The tree canopy is able to deflect up to 40% of precipitation from reaching the ground, with water absorbed through the leaves and evaporated back into the atmosphere.

Trees increase biodiversity

Over 30% of Australia’s threatened plant and animal species occur in urban areas. Trees, as part of an integrated ecological response to streets, parks and drainage corridors provide important biodiversity outcomes and support threatened species (DWELP. Trees for Cooler and Greener Streetscapes Guidelines for Streetscape Planning and Design).  Trees within urban communities enhance the biodiversity within environments through the provision of local habitat and of eco-corridors, providing food and habitat connectivity for native fauna.

Social benefits - Trees connect communities

Trees create sociable, comfortable, and enjoyable spaces. People are drawn to settings with beautiful trees, bringing together diverse groups of people within the public realm. Safe streets with an enveloping canopy invite public use for a range of social activities including walking, running and organised sports.

Trees are important in defining the character of communities, establishing a distinctive identity for local neighborhoods.  Whether it’s a memorable avenue, boulevard, signature tree or biodiversity expression, trees provide a sense of place that communities identify with. Assisting in the integration of minority groups and immigrants into the local community.  

Trees benefit our mental health

Walking through natural environments has shown to have improved the mental health of communities, as it provides an opportunity for quiet reflection and relaxation. Through doing so the individuals blood pressure and feelings of anxiety are reduced, while their mental acuity and memory recall is improved.

Interaction with the natural environment also has great benefit to children as it encourages creativity of the mind and experimental learning, the exploration and adventure of the natural world, and promotes physical activity, all of which correlates to the psychological wellbeing of children (Hansmann, R., S.M. Hug, and K. Seeland. 2007. Urban Forestry & Urban Greening).

Economic benefits

Trees are a valuable asset to the economy of local communities. They improve the aesthetic character of local neighbourhoods and increase the value of properties. Extensive research has also demonstrated that retail areas also benefit, with consumers spending up to 12% more in areas with the presence of large trees.

Trees are also an asset with a very high return, with each tree estimated to return $200AUD annually due to the extensive benefits they provide communities. In the City of Melbourne, the economic return of street trees was found to be significant, as the 70,000 street trees planted returned over $14million AUD per year (Beecham, S & Lucke, T. Street Tree Benefits and Challenges, 2015).  

Trees Increase Property Values

One study has found that a 10% increase in the street tree canopy within communities increases the value of properties by an average of $50,000 (AECOM, Economic Assessment of the Urban Heat Island Effect, prepared for The City of Melbourne, 2012).  And as trees grow larger, the value of properties grow proportionately (Beecham, S & Lucke, T. Street Tree Benefits and Challenges, 2015).