Are foreigners flooding from our national parks?

Like many environmental issues, the impact of exotic species has reached a stage where everyone acknowledges that there is a problem, but there is disagreement over how to solve it.

The report, Australia: State of the Environment 1996 identified introduced species as one of the top five threats to Australia's biodiversity. It also said that feral animals such as rabbits and goats are a major cause of land degradation.

But many in the community choose to target national parks as the root of the problem. The parks, they say, are sources of the weeds and feral animals that flood out onto the surrounding lands.

Their argument has two prongs: that introduced species flourish in national parks because natural vegetation is a safe harbour, and that these lands receive little management attention.

While large tracts of Australia carry native vegetation, only a small proportion of that area is in national parks. The largest area of vegetated land is on crown leasehold, which covers about 53 per cent of the country. Next on the list are public lands such as state forests and vacant crown land (30 per cent), and Aboriginal lands (13 per cent). National parks cover just eight per cent of the continent. So the responsibility for controlling Australia's feral animals is a broad one, not simply a problem for the national park managers.

As an illustration of the relatively minor contribution that national parks make to the rabbit problem, the Bureau of Resource Science has estimated that ripping rabbit burrows in the Western Division of New South Wales would cost $1.75 million for the national parks, and about $40 million for the grazing leases.

The question should really be: what is the importance of naturally vegetated lands versus cleared lands in contributing to the feral plant and animal problem? In many cases it is the disturbed country where the feral animals and weeds prosper, not the wild country.

In broad terms, there are more weeds in regions where land clearing has been most extensive. As the State of the Environment report says, this is partly because most environmental weeds are horticultural species that have escaped from cultivation. Many weed species have colonised national parks from the farming lands, not the other way round. As a result, our largest wilderness areas are the most weed-free places in Australia.

With feral animals, the story is more varied. Feral pigs prefer moist, secluded areas that are sheltered from temperature extremes. Clearly some of our national parks would be feral pig heaven. Likewise, goats survive in areas where patches of scrub or forest protect them -- not from climate extremes, because they can thrive in semi-arid places, but from human control methods.

Goat populations, however, are vulnerable to a natural control mechanism: predation by dingoes. These native dogs are also known to control fox populations in many regions. Foxes are most abundant in disturbed agricultural landscapes with a variety of cover, food and den sites. They avoid open country and closed forests, although they are regularly sighted around roads and fire trails in state forests in south-eastern Australia. It seems that the most fox-proof areas are those where dingoes are plentiful-- the large wilderness areas that have few roads and trails.

Feral cats are another case again, inhabiting the entire continent in varying densities. No single land tenure or land use is their natural home. Without a landscape-wide control scheme, they will be difficult to control.

The question of under-funded national park agencies failing to manage their lands is becoming less relevant. Governments are beginning to realise the conservation and `good neighbour' benefits of dealing with ferals and weeds. In New South Wales, for example, the National Parks and Wildlife Service now has pest management officers in each of its 27 districts, well ahead of the New South Wales agency responsible for vacant crown land. It is essential that all the managers in the landscape are able to work in a cooperative fashion, otherwise the efforts of national park managers will be fruitless.

Viewing one small part of the landscape as the root of all the problems is either naive or mischievous. Next time you hear such claims being made, take note of who is making the claim. Perhaps their motivation for pressuring the national parks authority is something other than a concern for the environment.