A recent study indicates an unsustainable koala population in South Australia's Mount Lofty Ranges, highlighting risks of starvation and habitat degradation. Simultaneously, conservation efforts on Queensland's Redlands Coast report a stabilization of koala numbers following significant historical decline.
These regional disparities reflect a national trend where koala populations in some southern Australian states face issues of overabundance, while those in northern states are listed as endangered due to habitat loss and other environmental pressures.
Regional Population Dynamics
Australia's national koala population is estimated by the CSIRO’s National Koala Monitoring Program to be between 729,000 and 918,000 individuals, a figure attributed to improvements in survey technology. Koala populations exhibit varied dynamics across the continent.
In southern regions, including the Mount Lofty Ranges in South Australia, French Island in Victoria, and Kangaroo Island, koala populations have experienced periods of overabundance. In contrast, koala numbers in north-eastern states, specifically Queensland, New South Wales, and the Australian Capital Territory, are in decline, leading to their classification as endangered by the Australian government in 2022.
Overpopulation in Southern Australia
In the Mount Lofty Ranges, research by the University of Technology Sydney (UTS), the Australian Museum, the University of Wollongong, and Flinders University indicates that the koala population has reached levels that pose risks of starvation and localized deaths. This region hosts approximately 10 percent of Australia's total koala population, with projections estimating a further increase of 17 to 25 percent over the next 25 years.
This growth is expected to impact food supply, vegetation, and natural habitats, potentially leading to die-offs of eucalyptus trees and other dependent species, and an increase in dead organic material that could fuel bushfires. Ecologists attribute this growth to favorable environmental conditions, including rainfall, temperature, and soil acidity, which support a suitable habitat.
Many of these overabundant koala populations, particularly in areas like the Mount Lofty Ranges and Kangaroo Island, are in regions where the animals were introduced in the 1920s, after the species faced threats from the fur trade. Koalas are not indigenous to these specific areas. In the absence of natural predators and diseases, their populations have thrived.
Professor Corey Bradshaw of Flinders University has characterized koalas in these regions as almost an 'invasive species,' a term used in the context of their introduction to non-native habitats and subsequent ecological impact, despite the species being native to Australia.
These areas often have abundant manna gum, a preferred food tree known for its high nitrogen, low toxin, and high moisture content, which can grow in monocultures supporting higher koala densities. Commercial blue gum plantations also contribute to increased koala populations.
Proposed Management Strategies for Overpopulation
Researchers suggest an annual sterilization of approximately 22 percent of female koalas in high-density areas of the Mount Lofty Ranges. This approach, identified through spatial modeling and a citizen science project, involves capturing individual koalas and administering a slow-release hormonal implant designed to prevent conception for the animal's lifespan.
The estimated cost for this population management strategy is $34 million over 25 years.
Professor Bradshaw indicates that hormonal fertility control is considered the most ethical population management method, noting that alternatives like translocation or culling can result in animal stress or public disapproval. Historically, a similar management approach was implemented on Kangaroo Island in 1997, where 12,500 koalas were sterilized and 3,800 were relocated.
South Australian Environment Minister Lucy Hood stated that while the Department of Environment and Water continues to monitor koala populations, there are no current plans for the implementation of such management tools.
Declining Populations in Northern Australia
In contrast to the overabundance in some southern regions, koala populations in Queensland, New South Wales, and the Australian Capital Territory face significant threats to their survival. The Australian government listed these populations as endangered in 2022.
The primary causes for their decline include:
- Habitat Loss and Fragmentation: Land-clearing and urban development have led to substantial habitat loss.
Analysis indicates that nearly 2 million hectares of suitable koala forest have been cleared since the species was declared threatened in 2011, with 81 percent of this clearing occurring in Queensland.
- Disease Outbreaks: Specific diseases contribute to population reductions.
- Direct Impacts: Fatalities result from vehicle strikes and dog attacks.
- Climate Change: Increased drought and bushfires pose threats to habitats and koala survival.
Redlands Coast Case Study
On the Redlands Coast, located east of Brisbane, the koala population experienced an approximate 80 percent reduction since the early 2000s, decreasing to an estimated 350 to 500 individuals. This decline was attributed to habitat loss from urbanization, road accidents, and dog attacks.
Since the late 2010s, the Redlands City Council has collaborated with university researchers on conservation initiatives. These include a mobile app, launched in 2020, which allows residents to report koala sightings or injuries, with some koalas fitted with Bluetooth ear tags to provide data. Efforts to reduce road deaths involve improved signage and experiments with artificial intelligence to provide real-time alerts to drivers about nearby koalas.
Research commissioned by Redlands City Council, conducted by Griffith University and the University of the Sunshine Coast, found no evidence of significant declines in koala abundance in the Redlands City local government area since 2019, suggesting a stabilization of the population.
However, researchers emphasize that the population remains critically low and vulnerable to threats such as floods and fires.
Development Concerns and Policy Advocacy
Despite the reported stabilization, Deborah Tabart, Chair of the Australian Koala Foundation, has expressed concern that this news might divert attention from ongoing threats posed by urban development. The Foundation has tracked a decline of 46,000 koalas in the Redlands, Brisbane, and Logan City areas since the early 1990s from an estimated 50,000.
A specific point of contention is Ormiston College's proposed campus expansion, which would involve the removal of approximately 600 koala-habitat trees. The Redlands City Council opposes this development, while the private school seeks permission from the state government, arguing that it would result in a "net-ecological gain" through the planting of additional eucalypt food trees. Disagreement exists regarding the classification of the trees proposed for removal, with some characterizing them as 'transitory' koala habitat, while others note that newly planted trees would require approximately a decade to mature. The Australian Koala Foundation advocates for a national koala protection act to prevent further clearing of koala habitat. The Queensland Deputy Premier is expected to make the final decision on the Ormiston College development.
Broader Significance and Future Outlook
Koala populations in South Australia are often regarded as an "insurance population" due to their stability compared to the endangered status of those in Queensland and New South Wales.
Experts underscore the importance of safeguarding native fauna, particularly given Australia's high mammal extinction rate. Actions taken to manage koala populations are seen as contributing to forest health and preventing species extinction.
Addressing these regional imbalances necessitates a holistic approach, including landscape-scale habitat restoration and the creation of mixed forests that do not foster excessively high koala densities. The southern states of Australia are predicted to become significant strongholds for koalas in a changing climate, making a sustainable balance in these populations crucial for the species' long-term survival.