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MIDWEEK MAGAZINE

THE VIEW from Mount Ross isn't

spectacular but like much of outback Australia it has a beauty of its own, and is somehow also quite restful.

To the south we could see several hun dred square kilometres of soft grey mulga covered ridges descending gently to the red and white ribbon of Lake Raeside twenty kilometres away. Close at hand the silver greys of wind-tossed mulgas contrasted with the golden orbs of flowering cassias.

We — Peter Williams from the Bureau of Mineral Resources and myself — were there to collect rock samples for age deter minations, and as we ate our lunch we could

pick out the dark green of the occasional kurrajong, and the eucalypt ribbons along the major watercourses.

Out here, in the dry heat of Western Australia, thirty kilometres west of Leonora and 250km north of Kalgoorlie, few drain ages warrant the lofty title of "creek".

One that does passes near Sturt Meadows homestead, where we ate dinner one night as guests of Lance and Norma Hurst.

Conversation covered the Leonora Pic nic Races and Dinner Dance the next day, the possibilities of some of Lance's gold prospects (not great), the level of support for the local Art Society (good), and conser

vation.

-Lance has been running regeneration ex periments on Stun Meadows for many

years now, and, like many better farmers,

has a good working knowledge of what the land can and can't take.

He is now turning his knowledge to good use by working as a consultant on regenera

A Canberra research centre is finding new ways to deal with an old rabbit problem as Robert Hill finds.

tion programs, particularly the regeneration of mine dumps. Given the economic state of rural Australia, he may need the extra

income to survive.

We took the opportunity to try to get answers to some questions of our own. Up on Mount Ross we'd noticed that about half the mulga was dead, and that although there were relatively few young plants, the older ones that had survived looked very healthy. The same was true of most of the area we had seen over the previous few days — about half the mulga was alive, old and very healthy, and half was dead and bleached white.

Over lunch we'd had a look around, and made a few guesses. Away from the surving trees the soil was hard and compacted (or non-existent), while beneath the protecting canopy of stiff branches there was usually a thick mat of twigs and dead leaves. A seed germinating on the hard ground between the existing trees would have a hard time of it. Precious rain would run off, rather than soak in, and away from the insulating mat of leaves summer temperatures would be

more extreme.

Perhaps the trees that had died were those that had lost their protective blankets. Why had the blankets gone? Were sheep or goats responsible?

We asked Lance if he had any ideas. What killed the mulga?

He had seen mulga killed by hailstorms, but that would give a patchy distribution, not a uniform pattern over tens of thou sands of square kilometres of country, which was what we had seen.

He couldn't help with timing either, other than add that there was little change in the appearance of areas covered by seventy year-old photographs.

So the mulga had died before about 1920, and we could guess that it might have gone during the Big Drought of the 1890s, the victim of sheep and their soil-compacting

hooves.

Even today, when stocking rates are usu ally carefully controlled in order not to fur ther degrade the carrying capacity of the land, the contrast between the often dense vegetation along fenced-ofl" roadsides and the much sparser vegetation inside the pad docks is a pretty sure indicator that some thing is different between stocked and unstocked areas.

Is it just sheep? After all, at the local stocking rates of about twenty hectares per sheep it can be a long way between animals.

Lance, along with some of the other local station owners such as the Finlaysons at Jeedamaya 100km to the south, have been cooperating with Western Australian gov ernment scientists in attempts to estimate kangaroo numbers.

Their results indicate that 'roos may ac

tually outnumber sheep; Lance's own sum mary is that sheep, goats and 'roos are equally bad if present in large numbers.

"What's the problem with the 'roos?" the city-based conservationists ask. "They're part of the natural environment, and should be left in peace."

True, except that the current population is way above the natural one. 'Roo numbers are up because of the provision of perma nent water. Intended for the sheep, water from station bores has proved a bonus for the 'roos, enabling them to get through droughts in much greater numbers than before the coming of the white man.

Now, because of the bores and the addi tion of sheep and goats, the area covered by a typical station might be feeding ten thou sand sheep, ten thousand 'roos, and several thousand goats, rather than the few thou sand 'roos that it would have carried, on average, two hundred years ago.

IN OTHER words, the land today is pro

viding feed for five to ten times as many

mouths as it did naturally. Something has to give, and slowly the land is being degrad ed. One small action — the provision of permanent water for sheep — has had an enormous and probably completely unpre

dictcd effect.

One thing that did surprise both of us was the relative scarcity of rabbits. Oh, they were certainly around, as the roadside meat market showed every morning, but were not (yet) in plague proportions.

A few more relatively good years, howev er, and it is a fair bet that they would be. Then they too would make their contribu tion to the continued slow ruination of Aus

frnlia's natural hrn'tnop

Although it seems that nothing much can be done about sheep, goat and 'roo numbers short of shutting down the stations, it ap pears that something can be done to limit the effect of rabbits. But that something has quite a kick in the tail.

Many Australians are aware that an earli er plague of rabbits was combattcd by the successful introduction into Australia of the Myxoma virus, a naturally-occurring or ganism which infects rabbits elsewhere, producing the disease myxomatosis.

Initially myxomatosis had a very high mortality rate, and almost all infected rabbits died. However, less-virulent muta tions of the virus soon appeared which killed fewer infected rabbits and which took longer to kill those which did die. These strains were favoured because the infection lingered, making it much more likely to be passed on to other rabbits.

Rabbits which recovered from a Myxo ma infection were immune to further at tack, and could go on breeding, which they promptly did. Thus the efficacy of the Myx oma virus as a control agent slowly de

clined.

Although various attempts have been made to reverse this trend, such as by rein troducing new lethal strains to selected areas, these new strains have not become established widely, largely because they kill infected rabbits too rapidly for continued spread of the virus to occur.

Until now. The .four decades since the introduction of the Myxoma virus have seen a tremendous growth in our under standing of how natural processes work, increasingly at a molecular level.

Advances in a range of fields now give scientists the possibility of changing select ed aspects of the Myxoma virus m order to increase substantially its effectiveness as a rabbit control agent.

Briefly, scientists working for a proposed Cooperative Research Centre for Biological Control of Vertebrate Populations spon sored by the CSIRO's Division of Wildlife and Ecology, the Australian National Uni versity, the University of Wollongong, the Agricultural Protection Board and the De partment of Conservation and Land Man

agement of the Western Australian Government want to explore the possibility that they can modify slightly the Myxoma virus so that rather than attack the mucous tissue of rabbits it will affect only the eggs and sperm, rendering infected animals ster ile but otherwise healthy. This approach of using the animal's own immune system to render it sterile is known as immunocontra ception. Such a modified Myxoma would have tremendous advantages, the chief one being that a$ it doesn't kill its host, there will be no strong pressure to select for a more benign form.

It also has one enormous disadvantage — the "sting in the tail" mentioned above — of which the Centre proponents are well

aware: foxes.

The large existing rabbit population sup ports a large population of foxes. Kill the rabbits, and the foxes look elsewhere for their dinners, most probably to native mammal populations. So, unless fox popu lations arc not substantially reduced first, a concerted effort to bring down the rabbit population would probably have the un wanted effect of devastating native fauna.

PERHAPS counter-intuitively, it thus

seems that any major program aimed

at reducing rabbit numbers must be accom panied or preceded by a substantial reduc tion in the number of foxes, an animal which many would think of as being one of the rabbit's few "natural" enemies.

The Centre proposes to address this prob lem by producing an immunocontraceptive agent for foxes as well as for rabbits.

Although the Centre has now been fund ed, much time will be needed before it is possible to assess whether it has achieved its stated goals.

Regardless of whether it is or not, the work done by Centre proponents to date provides another example of how careful we must be in tampering with a functioning ecosystem, even if it is a largely man-made one that we would prefer to do without.

Robert Hill is with the Research School of Earth Sciences, Australian National University.

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