While Australia's native kangaroos are not considered threats to local vegetation and land conservation, the species' species' increased overgrazing could start changing this condition, according to a new study.
Kangaroos are rarely seen as vegetation pests, mostly on farmlands where they share and compete for grazing lands against livestock. However, the same problem does not exist for the marsupials in conservation areas.
Researchers from the University of New South Wales Sydney report kangaroo overgrazing in some Australian conservation areas, adding that the condition has adverse effects on these locations' health and biodiversity. However, a surprising note from the researchers is that kangaroo overgrazing has more negative effects than rabbits, which are introduced species - not native to the area. Details of their study appear in the journal Global Ecology and Conservation.
Observing Kangaroos and Rabbits in Australian Conservation Areas
"The kangaroos had severe impacts on soils and vegetation that were symptomatic of overgrazing," notes Michael Letnic, senior author of the study and a professor of conservation biology and ecosystem restoration at UNSW Science, in a statement. He adds that the areas where too many kangaroos grazed had fewer species of plants. Furthermore, these areas suffered from nutrient depletion, and the soil was compacted, meaning that it can only absorb less water once rainfall arrives.
Researchers conducted fieldwork and examined conservation areas during the 2018 Australian drought - centered near New South Wales to arrive at their findings. The study covered four reserves located in semi-arid parts of the South Pacific continent. In these locations, both kangaroos and rabbits freely roam across the land. Furthermore, the conservation areas included small areas called "exclosures," which are fenced parts to keep unwanted animals from entering - including kangaroos and rabbits. These areas are designated as such to support the propagation of native and often threatened vegetation species.
Researchers then compared the quality of soil and vegetation between the outside and inside those exclosures - specifically noting the presence of land degradation signs associated with each species in relation to animal populations in the area.
The Kangaroo Overgrazing Problem
Kangaroos were found to be the most abundant herbivores in all four conservation areas.
"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," Letnic noted, adding how the kangaroo overgrazing has negative effects on biodiversity conservation. He also stressed the need to develop strategies that "restore the balance and reduce the adverse impacts of overgrazing," especially during drought.
Ecosystems are systems sensitive to a combination of different factors. In the case of Australian conservation areas, Kangaroo overgrazing has led to lower vegetation diversity. This, in turn, negatively affects soil quality and threatens the resources for other animals in the location.
"There isn't a lot of research about how kangaroos differentially affect different parts of the ecosystem," says Dr. Charlotte Mills, lead author and a visiting fellow at UNSW Science. She notes that most of the past studies tend to focus on rabbits. While rabbits also had negative effects on the land conservation efforts, these are not on the same level as with the kangaroos.
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