Ross Oke – Urban Forest Biodiversity Program / One Million Trees Program


This paper has been prepared in part as a case study to provide an overview of the aims and objectives of the Urban Forest Biodiversity Program.  It also seeks to identify potential areas where biodiversity conservation and education outcomes can be achieved through a focus on trees in urban environments, including streetscapes.

The Urban Forest Biodiversity Program does not have a major focus on street trees, particularly the practical issues involved in street tree selection and management.  However, there are some key areas where the program takes an interest in significant trees, remnant trees and vegetation, including opportunities to consider where improvements can be made in policy, legislative measures and management practices to achieve better outcomes.  It also actively promotes the use of local indigenous species beyond large-scale revegetation.


The South Australian Urban Forest Biodiversity Program (UFBP) has the unique vision of conserving the natural biodiversity of greater Adelaide – from Gawler to Willunga – from the coast to the eastern (watershed) boundary of the Hills Face Zone.

Grazing, agriculture, horticulture, residential development and industry have progressively all but replaced the unique flora and fauna of the Adelaide Plains to the point where we now have less than 2% of the original habitat left intact.  Where once 177 native species of bird lived, we now have only 112 remaining, and these must compete with 11 introduced species for the very limited and highly altered habitat available.

The UFBP aims to redress the loss of natural biodiversity in the metropolitan area, thereby enhancing the environmental sustainability, amenity and quality of life in metropolitan Adelaide.

Urban Forests are not a new concept.  Adelaide has had a number of greening programs which have contributed to the amenity of our city.  What is new is the concept of applying biodiversity planning to urban areas, and moving toward the goal of a sustainable ‘urban forest’ which conserves the region’s unique biodiversity – our natural heritage.

Although a series of wildlife reserves are already established in the Adelaide region, there remains a major challenge to extend these natural areas by including private land, creeklines, council reserves and other open space.  Street trees and garden plantings can also play a significant role.

The UFBP helps coordinate cooperation between local, state, national and international initiatives and strategies. Our goal is to involve all levels of government and the community in cooperating for biodiversity conservation, and to incorporate these considerations into planning and land management in the metropolitan area.

Focus on Priority Sites

The first priority for the UFBP is to protect what remains of the native flora and fauna of Adelaide.  The goal is to work by identifying habitats of highest priority for conservation, then identifying threats to conservation of these areas, and addressing those threats in the most effective way.  This may involve weed removal, fencing, changing management practices, buffering, linking and broad-scale revegetation using local native species.

Whilst the majority of these priority sites are located on the urban fringe and larger areas of open space that provide significant scope for revegetation, the program also supports projects that focus on using local species in various amenity and educational settings.

The UFBP is committed to promoting and advocating for the protection of biodiversity to ensure that future generations will have the opportunity to enjoy contact with the native flora and fauna which are unique to this part of Australia.

Why conserve biodiversity in an urban environment?

Knowledge of the complex and fragile interactions within plant and animal communities raises serious concerns about how we manage natural areas and natural resources.  We know that many aspects of cultural and technological development are not sustainable and often harmful to the environment.  Urban development, agriculture, industry, recreation, waste disposal, lack of understanding and poor practices are the main causes of vegetation loss.  With this comes loss of habitats, species decline and disappearance and the natural systems, of which they are a part, cease to function properly.  In addition to providing habitat for all forms of animal life, plant communities are the lungs of the planet – converting carbon dioxide (CO2) into oxygen.

More than eighty percent of Australia’s population live in urban centres located primarily on or near the coastline.  Land use and population pressures have impacted significantly on biological diversity in these areas and some historic plant associations have been completely replaced by urban development.  About ninety percent of the vegetation in the eastern temperate zone has been removed.  Often, it is only small fragments of the original vegetation that are left and these are under threat of further decline due to misuse, altered fire regimens, alien species and other factors such as aging, neighbouring land use and some forms of recreation.

The Adelaide region

The greater metropolitan area of Adelaide, South Australia, historically supported unique plant associations that have been progressively lost as the city and suburbs developed.  Heavy clearing was undertaken very soon after European settlement, and has continued into recent times.  In fact, agriculture replaced most of the indigenous vegetation even before suburban development made its impact.  The natural biodiversity of the Mount Lofty Ranges and Adelaide Plains was very high for an area with a temperate climate, partly due to the significant rainfall gradient and variation, from the hills to the coast, in topography, geology and microclimate.

Although Adelaide may be considered a very ‘green’ city, certain areas could be described as green deserts due to the lack of biodiversity, let alone natural biodiversity.  In any one location, there may have originally been hundreds of different shrub and ground cover species, while insect biodiversity in a particular place can amount to thousands of species.  The UFBP, drawing on the work of Darrell Kraehenbuehl, has produced maps in conjunction with Planning SA that outline the distribution of historic plant associations using a colour coded system laid over current suburb boundaries.  The species historically found in each association are listed on the back of the poster and can be cross-referenced as a planting guide for groups and individuals wanting to establish the original plants in their area.

This activity has been strongly supported by the UFBP and through the State Government’s new Urban Forests – One Million Trees Program will be significantly expanded upon.  Local councils and residents may, for example undertake cooperative backyard plantings to create wildlife corridors through their neighbourhoods.

Practical Conservation Strategies

There are significant constraints to protecting and enhancing biodiversity in a modern urban environment.  Excluding alien plant and animal species is difficult.  Cultural landscapes exist in response to our need for self-expression and reflect a tendency to reproduce examples of European landscapes.  Urban consolidation puts pressure on remaining open space and differing land use preferences often conflict.  Despite the constraints, there are still opportunities to protect what remains and to reconstruct habitats.  There is an immediate need to ensure that what is done now results in the best possible environment for future generations.

A representative sample of biodiversity can be preserved if about 10 percent of each habitat type is retained.  However, depending on the shape, size and links between areas, it is still likely that many plant and animal species will be lost.  The smaller an area of vegetation becomes, the less likely it is to be self-sustaining.  Historically, animal and plant populations were interconnected in a complex but continuous habitat mosaic that is now restricted to tiny remnants, many of which are too small or isolated to support viable populations.  Intervention is often needed to sustain the vegetation cover, and it becomes increasingly difficult to exclude alien plant and animal species.

Urban planning and development is undertaken with conscious purpose.  However, through the many attempts at beautifying and ‘improving’ our landscape we now have very little of the original expression of Nature’s palette.  This, combined with utilitarian needs such as food production, has led to the landscape in our urban area being almost completely replaced by a conglomerate of differing styles and tastes in landscape design, with patches of cleared land that can become infested with weeds.

The UFBP recognises the need to maintain cultural landscapes and provide for amenity, recreation and other land uses.  It does, however, promote the use of indigenous vegetation beyond the revegetation of larger parcels of land.  There are many opportunities, such as gateways to the city, for example, which could provide visitors with a sense of the unique character of Adelaide if local species were used rather than exotics that are planted in many other cities.  Simultaneously, maintenance costs, including the financial and environmental costs of irrigating exotic plantings can be significantly reduced.

The benefits of using local plants are being recognised within the parks and gardens and landscape design fraternity amongst other industry groups.  Of course, there is a recognised need to ensure public safety, especially regarding bushfire prevention, and that in some circumstances it may be inappropriate to establish dense vegetation for this and other reasons.  However, in all cases, the UFBP promotes the use of local provenance species, an aspect generally overlooked in many landscape developments.

Through the creation and preservation of urban forests, the UFBP and the Urban Forests – One Million Trees Program will enhance the environmental sustainability, amenity and quality of life of metropolitan Adelaide.  The over-riding emphasis is on the protection of remaining flora and fauna species and in revegetation using local native (indigenous) species.

Two themes emerging from a comparison of the “Urban Forest” with native Forest Management:

A natural forest or woodland complex implies a diversity of indigenous plant and animal species in an ecosystem with some degree of balance and equilibrium.  Sustainable management of native forests is not a new concept and generally involves long-term planning and management to ensure that whilst harvesting of forest resources occurs, the overall ecological functioning of the forest is maintained. Expanding on these two themes:

Urban Forest Ecology

The total biomass of vegetation in the Adelaide region is vastly different in composition to that which occurred prior to European colonisation.  In addition, we have significant structural elements, the most obvious being roads and housing but also including horticultural and agricultural production.  The altered landscape has resulted in a major loss of natural biodiversity (indigenous species, vegetation associations and ecosystems) and the establishment of a complex that favours certain introduced and more adaptable (increaser) native species.  Some of the key elements include a change in habitat structure, flowering times and available pollen and insect food sources.

The return of an historically natural balance in the built up area is prevented by these constraints, however as noted above, there are many opportunities to create natural areas using local species and practical steps that can be taken to encourage indigenous fauna to thrive.  The larger the available area, the greater the prospect of achieving a natural ecological balance, but even on a small scale populations of many species, including butterflies, small birds and reptiles can be established and conserved.  Local native plants are valuable in their own right and can be used in many settings to provide opportunities for a greater sense of contact with nature within the city and suburban environments.

“Forest” Management

Having trees as a major structural element, forestry involves ongoing assessment, planning and management to achieve sustainable harvesting of resources.  Applying a similar principle to components of an urban forest would suggest that planning, planting, managing and harvesting urban street trees would be a more sustainable approach to most current practices.  Many of the large remnant trees across Adelaide are a similar age and are collectively reaching the point where they are at risk of disappearing altogether.  In many areas, there are very few progeny to replace them.

Therefore we need to ensure that remnant vegetation areas and significant trees are properly protected and that future plantings are far more sustainable, through a combination of planting up areas which can develop into semi-natural forests and woodlands and through an ongoing management approach to large trees in more urbanized settings, such as streets.

Management could apply at a range of scales, from single streets, to local government areas and regions.  At the streetscape level, using North Terrace as an example, a longer-term management approach, drawing from sustainable native forest management principles might involve the selective, scheduled removal and replacement of trees.  In the urban context, replacements would be planted using advanced nursery stock.  Currently there is very little available advanced nursery stock of local indigenous species.

In discussing this idea with Tim Johnson (Treenet Chairperson) of West Torrens Council, it became apparent that, for example, a notional total of one hundred individual trees – such as SA bluegums – planted along North Terrace, at age fifty years, a removal and replacement (with say five-year old stock) regimen of one tree every year or two could be implemented to maintain a maximum terminal age of around one hundred and fifty years.   Some changes to legislation may be needed but the regimen could be flexible according to assessments of risk and tree health.  This approach would mean that the overall streetscape would maintain its character indefinitely.  Moreover, the resulting timber could be milled and used in public art projects, or perhaps to build furniture for significant public institutions.  This approach is in contrast to the “plantation” model that would remove all species probably in one go and start again from bare earth.  Trees established as longer-term elements within larger, semi-natural parks or open space areas would be allowed to mature within a more natural ecosystem – possibly even being allowed to regenerate naturally.

My Favourite Tree

Although it will always be a factor, we should move away from the subjectivity of plant selection that currently tends to pivot around the notion of personal preferences – “my favourite tree”.  A greater consideration of scientifically based criteria is essential in order to provide some sense of an overall framework for the total biomass within and surrounding urban areas.  Local, indigenous species should become part of this body of knowledge and the decision making process.  Our collective level of horticultural knowledge, albeit still with limitations, is significantly more attuned to the attributes of exotic species than our natural heritage.

We make decisions about plant selection based on a range of subjective criteria or based on desirable characteristics that we either justify as contributing to biodiversity by “increasing” it or we justify it simply because of the plant’s own merit as an element in the landscape. We make judgements based on some fixed criteria and other highly subjective criteria.

Plane trees, for example, are chosen often as street trees in Adelaide (and many other cites) for some very good reasons.  However, this has led to the species becoming almost ubiquitous.  In my view, this virtually puts the plane tree in the unenviable position of being the lowest common denominator in the decision making process.  As a child I recall a sense of appreciating the beauty of the Frome Road tree canopy between North Terrace and the Adelaide Zoo.  Yet through sheer overuse of the plane tree, this avenue and other features in our city are at risk of becoming mundane.  From a regional biodiversity point of view, the plants selected for North Terrace and other highly urbanised roads are relatively insignificant.  But from a biodiversity education point of view, and in terms of enhancing the natural character of the streetscape, the choice can be very significant.  Do we want to end up with homogenous landscapes to match our current homogenous built architecture?  Or can we create streetscapes and other landscapes that promote a greater sense our natural heritage?

Local species are adapted to local conditions.  Notwithstanding the constraints surrounding street tree selection and the fact that many sites may have modified topsoil and hydrological conditions, in many situations, there is no need to trial any so-called “better” species and in some situations (priority conservation sites), in line with the principles of the Australian Natural Heritage Charter, there should not be any use of exotic species.  As a principle, importing so-called “superior” species does not enhance biodiversity, even though some fauna will adapt well to the altered landscape.

There is an urgent need for further research into horticultural and arboricultural practices including risk assessment relating to the cultivation and management of large indigenous trees.  The work of Treenet is making a vital contribution in this area.  Our indigenous trees, including, for example the local Callitris pines are worthy of much closer attention as a highly appropriate species for many urban planting situations.  They are also in my favourite trees list but that is beside the point!

Many areas in and around our city provide ideal opportunities to highlight our local flora.

Opportunities and Constraints

Well-intentioned and appropriately articulated policies are rendered ineffective when they don’t translate into mechanisms (such as processes, plans and management strategies) that ensure their intent is realised “on-the-ground”.  Development controls such as the creation of building envelopes to protect significant vegetation including trees can achieve long-lasting outcomes.  An assessment of the ecological significance of an area earmarked for development should be the primary layer of information that is included in the spatial planning framework.  Simply laying a grid-like plan over an area without considering the immediate, let alone long-term implications is simply not consistent with Ecologically Sustainable Development principles, policies or practices.  Building envelopes need to give consideration to significant trees on adjoining properties.  Developments that occur without regard to the immediate and future needs of significant trees and remnant vegetation should be a thing of the past.

It is commonly recognized that a representative sample of biodiversity can be conserved if at least ten percent of each vegetation type is retained.  The size and linkages between areas is also critical.  If these criteria had applied to planning frameworks one hundred, fifty or even thirty years ago, our landscape would look very different, although the Adelaide Plains were largely cleared within a few decades after settlement.  We have tended to lay out a spatial development framework in a grid-like fashion across the landscape.

Not with standing the important concerns regarding shade (or lack of it) and the subsequent costs of cooling modern houses that straddle the bulk of the modern sized allotment, higher density housing can potentially provide opportunities for strategic use of public open space through the creation of natural areas using local species to maximize the benefits to natural biodiversity.  The challenge in this respect is to ensure that appropriate planning is applied for open space to accommodate a range of uses.  From a biodiversity point of view, having larger, linked areas of naturally vegetated land will provide a much better outcome for a greater number of native species in a more balanced ecosystem than the current mix of trees, shrubs, lawns and veggies grown on the now old fashioned quarter acre block.  The current mix of built and highly altered green space tends to favour native increaser species such as noisy miners and introduced species such as starlings.

Whilst significant tree provisions may go some way toward protecting large remnant trees, if we don’t intend to replant large indigenous species along streetscapes and in other built-up areas, their eventual total disappearance from the urban landscape, other than in reserves, seems likely.  From a natural heritage point of view this is a highly undesirable outcome and it is worth noting again that many of our large remnant trees are at a similar age and they are all well within the radar of potential litigation!  Better risk assessment and management practices were noted previously and dealt with in much more detail by previous speakers at last year’s Treenet Symposium.

Two other possible strategies might include the planting and management (using the “forestry” principles outlined above) of local species including large gums in streetscapes and the establishment (starting now) of more sustainable plantings using their progeny.  The challenge for the more urbanised parts of our city is to find suitable locations.  The SA Urban Forests – One Million Trees Program is keen to work with land managers, planners and communities to identify local parks, creeklines and other areas of open space where such plantings can occur.  In addition, we would welcome the opportunity to incorporate some local understorey species to provide for more “natural habitat” for the local residents and hopefully for some of the local wildlife.


There is a definite link between biodiversity conservation objectives and urban street trees.  Whilst the main contribution of street trees is probably with respect to amenity, shading and air quality, there are also potential water conservation and water quality benefits to be achieved.  Ecological information, particularly empirical data relating to urban trees is primarily focused on carbon lock-up, shade and cooling, air and water quality and to a lesser extent, amenity.  Biodiversity considerations are often either misunderstood or not considered at all.  Biodiversity conservation extends to the species level and as such, along with educational opportunities, there is a role for local indigenous species in streetscapes, smaller local parks and gardens.

A focus on threatened species and remnant vegetation along with significant trees is a priority for biodiversity conservation.  However, there are opportunities to highlight our local flora even in streetscapes.  This approach can assist in providing a greater sense of connectivity between people and our natural environment and stronger support for broader sustainability goals.

Research, through groups such as Treenet, the Centre for Urban Habitats, the Urban Forest Biodiversity Program and others is vital to provide a basis for informed decision making.

Risk management and management in general, are critical areas applying not only, but particularly to indigenous species.  The wonderful mature (in particular remnant) large trees, particularly gums, which exist within our cities and towns are at risk of being removed and never replaced in streetscapes and realistic strategies are needed to redress this.

The nursery and landscape industry will develop greater capacity in response to a greater demand for local species for use in a range of urban landscape settings.


Australian Heritage Commission, (1996). The Australian Natural Heritage Charter: Standards and Principles for the Conservation of Places of Natural Heritage Significance. Canberra.


Further Information on the Urban Forest Biodiversity / One Million Trees Programs


  • Identify priority areas and land linkages
  • Galvanise planning and action strategies of relevant Authorities
  • Support the collective effort to conserve biodiversity
  • Work with Community Groups to maximise outcomes for effort
  • Influence organisational change. Raise practitioner and public knowledge through education, training and communication

Activities and Programs

  • Assistance with planning, funding and coordination of site works
  • Provision of information, resources and training to local organizations and community groups
  • Raisingawareness of biodiversity issues and
  • Ensuring that biodiversity is considered when regional development and local management plans are produced

Local Action:

On-ground projects including habitat restoration and revegetation are implemented locally by;

  • Facilitating best practice in the care and management of natural heritage sites
  • Providing specialist advice and support to assist in implementing identified regional priorities
  • Working with Councils to promote communication and consultation on local native vegetation conservation
  • Assisting community groups in achieving their goals for biodiversity conservation in the local area
  • Seeking and securing additional funding and support for local projects including assistance with NHT funding applications and monitoring projects funded through the NHT

Project Officers based at local councils coordinate action at the local level. Each project identifies the interest groups as a starting point and proceeds from there.

Targeted Projects:

On-ground action is directed to priority sites identified in the biodiversity plan. To date; protection, management, revegetation, restoration projects totalling around 1,000ha have been implemented.

Examples include;

Priority Plant Associations

  • Eucalyptus microcarpa (Grey Box), Eucalyptus porosa (Mallee Box) and Banksia marginata (Silver Banksia) Woodlands poorly conserved Statewide. Protection of remnants through “bushcare” approach and “Buffers to Bushland”
  • Minimal disturbance techniques to sensitive areas to remove weeds.
  • Management of threats and threatened species.
  • Fencing and targeted revegetation using local species aimed at buffering existing native vegetation which is currently being adversely affected at edges.

Larger scale projects designed to show best-practice on an issue or site of particular importance to the region’s biodiversity.

Regional Partnership Projects

  • Joint projects to address priority issues on a bio-regional, catchment or sub-catchment scale.
  • Creek-lines, road corridors, the Hills Face Zone.
  • Joint projects with Planning SA and Councils such as Field River Revegetation in association with new housing development.
  • Large-scale corridor revegetation projects in the Willunga and Northern Adelaide Plains through the One Million Trees Program.  One hundred hectares of revegetation planned and commenced for the City Parklands.  Large-scale revegetation planned or commenced with the City of West Torrens.  Smaller projects in local reserves that provide an opportunity to demonstrate how local species can be used in a landscape treatment.

The One Million Trees Program will establish over 1,000 hectares of trees and associated understorey species throughout the Adelaide metropolitan area over the next four years.  It is estimated that this will achieve significant gains for biodiversity conservation, air and water quality, and will sequester over 300,000 tonnes of CO2 equivalents at maturity.

Grants Program:

Funds are available for smaller on-ground projects that meet the program’s objectives and priorities. Projects include;

  • Remnant vegetation protection and habitat restoration
  • Targeted revegetation with local species
  • Trials and projects with an educational focus leading to improvements in on-ground management
  • Projects that achieve multiple outcomes such as improvements in soil and water quality
  • Projects that combine natural heritage protection with elements of cultural (in particular Kaurna) heritage So far over 300 projects have been funded.
  • Applications are assessed every 6 weeks
  • Applications can be made at any time throughout the year.

Community Involvement:

The UFBP has around 300 groups recorded on a database and spatially located on GIS. We actively assist in engaging local government or other authorities with local groups.

  • Local expert knowledge is sought and used by UFBP and we also undertake projects designed to foster increased participation in local projects by the wider community.
  • The UFBP supports programs such as Friends of Parks, Trees For Life Bushcare, Coastcare, Landcare and Greening Groups. We have teamed up with Our Patch on a large number of project sites

Targeted education and training programs;

Aim to increase understanding of biodiversity and improve decision-making and management practices:

  • “Bio-What?” education kit for schools with regular updates and projects
  • Seminars for local government staff and elected members
  • Internet site including fact sheets, newsletters, “Bio-What?”, order forms for resources
  • A regular newsletter and other issue specific newsletters
  • Workshops for community groups to assist in developing effective habitat restoration projects
  • A communication strategy to assist in targeting and coordinating communication including media releases
  • Displays at events such as Womad, the Royal Show, field days etc.
  • Support for employment training schemes operating within the region on specific projects
  • Provision of information and presentations to TAFE and universities


Information resources have been developed, are distributed free or at cost and so far include;

  • Data base/contact list of community groups in the region
  • Historic plant associations maps
  • Regional fauna / habitat map
  • Education kit for schools
  • Fact sheets and resource lists including information on specialist contractors
  • Information on regional priorities
  • Native freshwater fish poster
  • Bibliography of biodiversity related plans and strategies