Street trees and suburban biodiversity

Native and exotic trees along Canberra street. Photo: F. Howarth.

Native and exotic trees along Canberra street. Photo: F. Howarth.

Suburbs are home to an increasing proportion of the world’s human population. In Australia, some of the strongest population growth is occurring in the outer suburbs of major cities.[1] Suburbanisation is a divisive issue in ecological debates, with strong advocates for and against urban sprawl. In Triumph of the City, Edward Glaeser criticises suburbs for their negative environmental impacts, while Patrick Troy comes to the defence of suburbs in the essay: ‘Saving our cities with suburbs.’[2] Both the negative and the positive effects of suburbs are present in Canberra, Australia’s “Bush Capital.” As suburbanisation is a global trend, it is necessary to consider how we can conserve biodiversity within suburban environments.

Expanding suburbs encroach on the surrounding landscape, paving over native vegetation, fragmenting habitat with roads, and introducing new threats to local wildlife, such as cats and dogs. However, just as humans colonise this newly claimed habitat, a variety of animal species carry out a colonisation of the suburban environment. As suburbs expand, they become home to an increasing number of animal species, especially birds. Suburbs present a key advantage over denser urban development, as there is space for suburban trees, which provide an important habitat for many bird species.

Public enemy number one. Photo: F. Howarth.

Public enemy number one. Photo: F. Howarth.

Suburban trees include street trees and trees in public parks. Canberra’s street trees include a mix of native and introduced species. Native trees provide habitat for many bird species within suburbs. Indeed, a recent study conducted by researchers at the Australian National University (ANU) demonstrated that native suburban trees are important for bird species richness.[3] The age and structure of stands of trees is also important. Mature trees (100-150 years or more) develop hollows, which provide homes for birds, some mammals and insects.[4]

This means that managing suburban trees is important for conserving urban biodiversity. Indeed, these findings mean that we should look to maintain a high proportion of native trees within Canberra’s suburbs, and that we should retain older trees, and allow more young trees to grow to maturity.

However, implementing these management strategies is complex. In fact, suburban tree management must contend with competing values. Many Canberrans prefer exotic, deciduous trees near their homes, because they provide shade in summer, while letting in sunlight in winter. Exotic trees are often seen as safer, as eucalypts are prone to dropping branches. Additionally, residents value the aesthetics of introduced species. So how can we reconcile these values with urban biodiversity conservation?

Fortunately, there are some management options that satisfy most requirements. Indeed, according to the ANU study, assuring that at least 30 % of suburban trees are native would significantly increase bird species richness within Canberra.[5] This means that we can continue to plant deciduous trees near houses and infrastructure, and plant native species in areas where they are less likely to produce negative consequences. In addition to this, mature trees should be maintained where possible, though this may require safety measures to minimise the risk of injury and damage caused by falling branches. Clever management can ensure that we continue to enjoy the sight and sound of native birds in our suburbs.



[1] Australian Bureau of Statistics 2013, Regional Population Growth, Australia, 2011-12, Australian Bureau of Statistics, viewed 30 May 2013, .

[2] Glaeser, E 2011, Triumph of the City: How urban spaces make us human, Macmillan, London; Troy, P 2005, ‘Saving our cities with suburbs’, Griffith REVIEW, ed. 2.

[3] Ikin, K, Knight, E, Lindenmayer, DB, Fischer, J & Manning, AD 2013, ‘The influence of native versus exotic streetscape vegetation on the spatial distribution of birds in suburbs and reserves’, Diversity and Distributions, vol. 19, no. 3, pp. 294-306.

[4] Gibbons, P & Lindenmayer, D 2002, Tree hollows and wildlife conservation in Australia, CSIRO, Colligwood.

[5] Ikin et al. 2013, p. 299.


About Biodiversity Conservation Blog

I am an Associate Professor at The Australian National University and convene a (very awesome) course called Biodiversity Conservation. Myself and students in the course contribute to this blog.
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One Response to Street trees and suburban biodiversity

  1. Excellent Freya. An issue that deserves greater debate. Another PhD student at the Fenner School (Darren LeRoux) is looking specifically at the value of mature trees in urban Canberra.

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