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Managing feral pigs, pond apple and gamba grass on Cape York

Words Sandra Lloyd | Photo Cape York NRM

Freshwater rivers and creeks in northern Australia have cultural, environmental and economic value. These values are under threat because of introduced species including Pond Apple, Gamba Grass and feral pigs.

Pond Apple (Annona glabra), originally imported to Australia in 1912 as rootstock for Custard Apple, is a major weed impacting mangroves, rainforests, and drainage systems including creeks, riverbanks, coastal dunes and wetlands along the eastern coast and the tip of the Cape York Peninsula. Seeds are spread by water and animals, including feral pigs. Pond Apple is a WoNS (Weed of National Significance) and a Class 2 Declared Weed. It is a serious offence to introduce, keep, or supply Pond Apple in Queensland. Penalties of up to $80,000 can apply.

Gamba Grass (Andropogon gayanus), was introduced from Africa as a pasture grass and is now one of the biggest threats to the natural health of Cape York.  Growing to four metres in height, Gamba Grass carries four to five times the fuel load of native grasses and burns very fiercely - over 1000 degrees compared to around 350 degrees for native grasses. Gamba Grass fires readily kill native vegetation, tall trees included, turning woodlands into grasslands and causing local extinctions of both plant and animal species. These hot, intense fires place people and property in danger. Fire benefits the plant, helping to disperse the abundant seeds it produces. Gamba Grass has also been declared a WoNS!

Feral pigs are descendants of the domestic pig, Sus scrofa. Pigs were introduced to Australia via the First Fleet. Stock could wander and by the 1880s pigs had run wild in NSW and spread north. They are now the most widespread and damaging feral pest on Cape York. Conservatively, there are four million feral pigs causing broadscale damage to wetlands, rivers and streams. This is due to their rooting behaviour which can severely disrupt the composition of the soil’s microorganisms, and subsequent nutrient cycling, disrupt the regeneration of plants, change the composition of the plant community and allow water erosion to occur. Feral pigs are also a key threat to turtle nests which impacts marine turtle populations.

Solutions

The need to strategically control these high priority regional pests and weeds is part of Cape York NRM’s ‘Maintaining the reduction of vertebrate pests and weeds on Cape York: Strategic targeted control of high priority regional pests and weeds’ project. Activities include the eradication of Gamba Grass in Injinoo and Napranum through control works and mapping treated areas containing Pond Apple on the east coast of Cape York, and targeted control of feral pigs.

As part of the program, Rangers from the western Cape are working to reduce depredation to 30 percent (or less) of marine turtle nests. The Rangers also work to reduce the impact of feral pigs on individual turtle nests. As part of the Western Cape Turtle Threat Abatement Alliance, these activities represent part of the ongoing effort to reduce the potential impacts of feral pigs on nesting marine turtles.

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Sandra Lloyd
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