Monday, 12 November 2012

High wallaby densities impacting environment and production

High wallaby numbers in the Adelaide River Catchment dig for resources (G. Sawyer)

A new pasture in this paddock failed due to wallaby grazing impeding establishment (Douglas Daly Res. Farm)

Increasing numbers of wallabies are becoming one of the biggest pest issues for farmers and pastoralists in the tropical savannas. Populations appear to expand in response to increased water availability, supplement and other factors. I spoke to a number of pastoralists who explained that the problem is not just about lost production.

Dense wallaby populations can impact the environment. I have heard numerous accounts of overgrazed river corridors in areas where cattle have been excluded with fencing, and the increase in bare ground promoting weed establishment and possibly erosion.

Wallabies also impede sustainable agriculture by grazing spelled or burnt pasture, or newly planted crops or pastures. In cell grazing, cattle are removed after grazing to give the area a spell. However, wallabies are attracted to the shorter grass and graze uncontrolled, nullifying the removal of cattle. They also hit green pick on burnt or establishing pastures and contribute to reduced ground cover during erosive early wet season rainfall. Loss of ground cover and fuel load reduces the utility to use fire to control woody thickening.

Forage budgeting in cell grazed paddocks is also affected. Phil Howie from Maneroo Station recorded a paddock that had 150 grazing days for the dry season, but when cattle were moved to it six weeks later wallabies had reduced this to 40 days.

Some now consider wallabies as a major impediment to property development.

Fencing to 1150mm high with different combinations of barbed wire and electric fencing has been tried with varying degrees of success, but may only be justified for high value crops.

Fencing with pig mesh tends to move the problem into nearby river corridors or to neighbours. Fenced out wallabies have camped at a new fence for some time and overgrazed the site and eventually starved.

So what about shooting? I have heard of permits to shoot up to 3,000 wallabies, but more commonly pernits for 500 animals are permitted. The problem is that shooting at this scale appears to be ineffective with little impact on numbers. It is generally considered to be a costly waste of time, and permits are often not actioned.

What about dingo / wild dogs controlling wallabies? There are very few pastoralists that want to expose their herd to dog attack for both production and animal welfare reasons, so most control dog numbers, not promote them.

The problem remains unsolved, but with increased water availability planned for most pastoral leases,  its likely to get worse. Ultimately, some populations will reach carrying capacity and may crash with disease, as appears to be happening in one agricultural region.

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