Planting trees halts koala decline

Koalas are declining across NSW as a result of deforestation, habitat fragmentation and disease. Image: Shutterstock.

A new study has identified high-risk areas for koalas.

Researchers from the University of Sydney have found that planting trees can help expand koala habitat and increase their numbers. They also found that the koalas were most at risk when they live in small patches of bush near roads and train tracks, as they observed high mortality rates in these areas.

Dr Matthew Crowther says that koalas are declining across the state, but a few areas were identified where the koala populations were increasing. “We did a state-wide survey of koalas with the NSW Government and found that Gunnedah was one of the few places that appeared, against the state trend, (to be) increasing in population.”

“We also knew of the massive tree planting campaign in the 1990s, and we wanted to test its success.”

70 koalas in Gunnedah were fitted with GPS collars for the study, allowing scientists to track them over an average period of three months. The results suggested that koalas aren’t limited to old growth areas, but were also using the newly planted eucalyptus trees, which may be the cause of the population increase.

Unfortunately, this means that the koalas are using trees planted next to roads and train tracks. They also appear to be limited to a range of two kilometres, mostly in small patches of trees.

Dr Crowther says this limited habitat may be an issue for their survival, as the limited patch size affects their access to food and water. “Travel between patches is risky, due to exposure to cars/dogs and other threatening processes. Hence access to mating partners can be difficult for some individuals, and lack of movement can limit genetic diversity.

“In theory lack of diversity makes populations susceptible to disease- the Tasmanian Devil is a perfect case of this- but I think the lack of access to year-round shelter, food and water resources would be more of an immediate killer.”

Instead, simply planting the right trees in the right areas could expand their habitat and give the koalas more options and less competition for food and water. “Connectivity between patches- both old growth and new plantings- is essential for long-term survival of the populations.”

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