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Kangaroos prove more damaging than rabbits

Kangaroo numbers have reached levels that are contributing to drier soil and less vegetation – and our national emblem may even be more damaging to conservation areas than rabbits.

A new collaborative study led by UNSW Sydney found that conservation reserves are showing signs of kangaroo overgrazing – the level of intensive grazing that negatively impacts the health and biodiversity of the land.

The kangaroos’ grazing impacts appeared to be more damaging to the land than introduced rabbits.

Included in the study was Boolcoomatta Reserve near Cockburn SA, 100km west of Broken Hill.

Professor Michael Letnic, the senior author of the paper, says the kangaroos had severe impacts on soils and vegetation that were symptomatic of overgrazing.

riveren kangaroo 2

Kangaroos grazing impacts appear to be more damaging to the land than introduced rabbits in times of drought. Pic: Professor Michael Letnic

He says not only did the areas grazed by overabundant kangaroos have fewer species of plants, but the soils were depleted in nutrients and were compacted – which means that less water can be absorbed by the soil when it rained.

The findings, published late last year in Global Ecology and Conservation, are based on fieldwork conducted in conservation areas during the drought in 2018. 

"We need to start thinking about developing strategies to restore the balance and reduce the adverse impacts of overgrazing – particularly during times of drought.” - Professor Michael Letnic. 

Kangaroos were the most populous herbivore across all reserves.

“We tend to think of kangaroo grazing as a natural process because they’re a native species, but there are now too many kangaroos in conservation reserves,” says Professor Letnic.

“Their grazing can be detrimental for biodiversity conservation.

"We need to start thinking about developing strategies to restore the balance and reduce the adverse impacts of overgrazing – particularly during times of drought.”

Dr Graeme Finlayson, SA Arid Rangeland ecologist for Bush Heritage, says overgrazing had dire implications for other native species who rely on vegetation cover and associated food resources to survive.

Dr Finlayson says one of the key species that is likely to be impacted by overgrazing at Boolcoomatta is the critically endangered Plains Wanderer (Pedionomus torquatus), of which there are less than 1000 left in the wild.

Despite sighting three birds at Boolcoomatta in May 2019, monitoring on the reserve has failed to detect any birds since then.