An urban forest is defined as all of the trees and shrubs on all public and private land in and around urban areas (including bushland, parkland, gardens and street trees) and is measured as a canopy cover percentage of the total area.

It is a term now widely accepted in town planning and environmental management and has become more widely known in the general community. An urban forest is recognised as a primary component of the urban ecosystem.

Urban forests play an important role in the ecology of our human habitat in many ways: they filter air, water and sunlight, and provide shelter to animals and recreational areas for people. They moderate local climate, slowing wind and storm water, and shade homes and businesses to conserve energy. They are critical in cooling the urban heat island effect, thus potentially reducing the number of unhealthy ozone days that plague major cities in peak summer months.

In Australia there is already wide-ranging activity to protect and grow our urban forests -

• In Victoria, the City of Melbourne has developed its Urban Forest Strategy to manage and replace the loss of up to 44 per cent of its current tree population in the next 20 years

• Sydney City Council has launched a major tree planting program aimed at increasing tree canopy coverage by 50 per cent over the next 20 years

• SA Urban Forests Million Trees Program achieved its goal in 2006, and now has a target of three million native plants across the greater Adelaide metropolitan area by 2014

• The ACT Government has been committed to ensuring Canberra’s urban forest is maintained and further enhanced through the Urban Forest Renewal Program

• Brisbane City Council has a Two Million Trees project underway and wants to achieve 50% tree shade cover for footpaths and bikeways by 2026.

BUT, there is a need to do much more to maintain and grow our urban forests and importantly, get community recognition that everyone can play a part in the urban environment. Many local councils are yet to embrace this need and too many homeowners consider trees are only suited to public spaces.

Local government needs to improve the diversity of their plantings and take advantage of trees already proven to offer benefits such as:

• reduced expenditure on replacing inappropriate trees

• reduced tree maintenance costs

• increased efficiency in street tree management

• reduced hazard associated with inappropriate species and/or maintenance

• reduced impacts on catchments, and reduced costs associated with catchment pollution

• reduced impacts on infrastructure and utilities; reduced maintenance – pruning, road sweeping, road reconstruction, curb and water table reconstruction, footpath reconstruction.

 

How do we value the urban forest?

 

Despite the fact that trees are major urban infrastructure assets, in the past decade tree populations in many Australian cities have declined, particularly with the loss of private open space.

A study in the US found that every dollar invested in urban tree management returned annual benefits ranging from $1.37 to $3.09 (US). These benefits can include energy savings, capital appreciation, storm water management, air quality (reduced pollution) and carbon sequestration.

The gross annual benefits for a typical street tree in Adelaide were estimated at $424.40 and assuming a 60 year average life cycle the estimated gross benefit per tree is more than $25,000.

The benefits of urban trees and landscapes already mentioned have not included how gardens improve human heath, extend life spans, lower blood pressure and generally improve our health and wellbeing. When combined these attributes can save our society a vast amount in medical and social infrastructure costs.

iTree

Trees provide numerous aesthetic, social and economic benefits but also incur some costs. The biggest cost of trees occurs when they are purchased and planted. Possible watering during initial care, leaf, branch and whole tree removal at the end of their life are also expensive. To function well in an urban landscape, trees generally require some form of maintenance.

These costs are often brought to the forefront without considering the benefits, particularly and specifically the measurable ones such as economic and environmental. Current tools provide some measurement, but now a tool new to Australia will allow a community to put a value on the benefits associated with their urban forest.

iTree is the most comprehensive software developed to date to quantify the economic and physical benefits of an urban forest. The i-Tree tools were originally developed by the United States Department of Agriculture’s Forest Service to aid in urban and community forestry analysis and benefits assessment.

A partnership between Nursery & Garden Industry Australia, Aboriculture Australia, the Cities of Melbourne and Sydney and Enspec Pty Ltd consultancy as led to the development of an Australian version of the software.