IT鈥橲 10 am and 43 掳C. The road to Alice Springs is almost too hot to
touch, a shimmering blue vein in a moonscape flat and red. You can drive all
day in the outback passing nothing but roadside filling stations selling 鈥渞oo鈥�
pie and Aboriginal artworks, their dreamtime images as flat as the squashed
goannas on the road. The scenery is as persistent as the local flies: a
breathtakingly silent expanse of parched grasses clinging to cracked clays and
dunes, dotted with gum trees, acacias and gnarled shrubs. Hard to imagine the
vegetation blooming, as everyone says it does, after rainfall.
Most visitors come here to pay homage to Ayers Rock and the other sandstone
monoliths that leaven the landscape like experimental sculptures from another
world. But there are other curiosities to savour. Outback Australia is home to
more species of reptile per square kilometre than anywhere else on the globe.
Home, too, to one of the world鈥檚 most erratic and unpredictable climates. An
area may go weeks, months, even years without a sizable downpour and then be
hit by flash floods and creeks running ten feet high. Less obviously, this is
also the scene of one of Australia鈥檚 most enduring ecological mysteries 鈥� the
case of the vanishing outback mammals.
Over the past 200 years, more than half the mammal species that once graced
the arid grasslands and billabongs of central Australia have disappeared,
landing the region with an unwanted world record in extinctions. Gone for ever
are animals like the plains rat kangaroo which once lived on the fringes of
the Lake Eyre basin, and the stick-nest rat that once eked out an existence in
calcareous outcrops. Reduced to tiny, fragile populations are animals like the
Western quoll and numbat. And symbolising their struggle is the bilby, a
rabbit-sized mammal whose dwindling numbers have become a national cause
ce麓le麓bre. If bilbies could be cuddled on camera, Australian
politicians would probably rise to the challenge.
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Why the sudden wipe-out? Fingers instinctively point to the cats and foxes
that came with the Europeans. But this is a whodunnit in the classic mould:
the obvious suspects don鈥檛 fit all the puzzling facts of the case. Missing
from the extinction list are lizards, snakes or other reptiles. Cats eat
lizards, too, don鈥檛 they? Most of the extinct and endangered species are
medium-sized mammals (why would predators spare the tiniest seed-eating
rodents and bigger mammals?). And last but not least is the awkward absence of
humans. Outback Australia is a place white people drive through but don鈥檛 live
in; it makes the Kalahari look congested. Why would it lose more mammals than
the wetter, industrialised southeast? Cats and foxes live there, don鈥檛
they?
Answering such questions has arguably never been more important for the
people of inland Australia. Since the first white settlers arrived at the turn
of the century, its economy has depended mostly on cattle grazing. If current
trends are anything to go by, those days may now be numbered. Families that
have been on the land for decades are selling up or reducing their stocks.
Would-be newcomers enticed by the cheapness of the land 鈥� a hectare of pasture
will cost you the equivalent of a few pounds 鈥� are finding banks less willing
to lend. And as the grazing-based economy falters, people are beginning to
look to ecotourism as a way of filling the gap.
A poor record on mammal extinctions is hardly the ticket here. Despite the
fact that most of the mammals in central Australia are nocturnal, burrowing
creatures, their demise is certain to bother ecotourists searching for
pristine landscapes. Can a landscape lose half its mammal species and still be
called pristine? Doesn鈥檛 it all add up instead to an ecosystem in serious
decline?
No better place to find out than Alice Springs itself. Forget images of a
flyblown frontier town; A Town Like Alice was written nearly half a century
ago. Alice today is a modern melange of air-conditioned hotels, banks and
shopping malls, a want-for-nothing place which can even offer you that most
surreal of Australian luxuries: a surf shop in the middle of a desert. More to
the point, the town is home to the CSIRO鈥檚 Centre for Arid Zone Research,
where some twenty scientists face the forbidding task of keeping tabs on this
vast landscape.
It鈥檚 not all Akubra hats and sun-baked days in the bush. The researchers
certainly do field work, but their main tools are satellite images and
sophisticated computer programs that can turn those images into ecological
trends, such as changes in vegetation cover. And the message from space is
hardly reassuring. It suggests that the plight of the native mammals is bound
up with the declining fortunes of the graziers. Both trends reflect losses of
habitat, vegetation and soils, says Steve Morton, the station鈥檚 principal
ecologist. The big difference is that while the grazing animals are part of
the cause of the change, the native mammals are its innocent victims. The land
has been repeatedly overstocked, says Morton: it has been mined, not
farmed.
Folk consciousness
Serious charges indeed 鈥� and not just for biological reasons. The
pioneering image of the farmers who settled the outback runs deep in the folk
consciousness of white Australia. They were the evidence that the lands could
be tamed and exploited in the European tradition. For decades, explains
Morton, the social and cultural incentives for keeping such farmers in place
overwhelmed all other considerations.
Now the scene is set for change. Multiculturalism is in the ascendancy, as
is an Aboriginal land-rights movement that will return vast swathes of the
outback to its traditional owners. Gone are the regular drought subsidies that
kept the graziers going despite catastrophic losses of stock. Gone, too, are
hillbilly attitudes to conservation. 鈥淟andcare鈥� programmes designed to
resuscitate degraded landscapes and stem further damage are almost a national
obsession.
Much of this is reflected in Morton鈥檚 own career. When he arrived in Alice
Springs 10 years ago, the station鈥檚 remit was to find ways of maintaining
pastoral production, of sustaining the land鈥檚 sparse and unreliable output of
digestible grasses. Now conservation has become the dominant issue.
鈥淏iological diversity is no longer just something we need to feel good about,鈥�
he says. 鈥淚n the long term, it will bring in an enormous amount of money.鈥�
Even if the land continues to be degraded? Here one senses some
frustration. Cagily Morton speaks of 鈥渁n inherent conservatism built in by the
political linkages the pastoral industry has established over many many
测别补谤蝉鈥�.
In the past, that conservatism has thrived on inconclusive, sometimes
conflicting data about land degradation. Nobody doubts that Australia has a
problem. For years, the nation鈥檚 media has been full of the woes of vanishing
topsoils, of arable lands ruined by salinisation, of grasslands degrading into
unpalatable shrublands, of drought-beleaguered farmers forced to shoot their
stock, of conservationists explaining that Australia鈥檚 vegetation and soils
(the thinnest in the world) were 鈥渕ade鈥� for soft-footed kangaroos, not hooved
ruminants. And so on. The problem for conservationists is that proving the
equation, excessive pastoralism equals loss of vegetation equals loss of
biodiversity, is another matter. Pulling a string of ecology papers from his
office filing cabinet, Morton explains why.
One problem is the erratic climate. Unpredictable rainfall 鈥� it might be
100 millimetres one year, 600 the next 鈥� makes the environment inherently
changeable. Droughts shrink the small islands of fertility that are centred on
the flood plains, creeks and billabongs; big rains green broader swathes of
the landscape and replenish the water tables. What looks seamless from the
road is really a shimmering and shifting patchwork quilt of different
vegetation types 鈥� tussock grasslands, spinifex grasslands, mixed woodlands,
acacia trees, chenopod shrublands. It鈥檚 all too easy to mistake temporary
losses of vegetation during a minor drought as evidence of soil erosion. And
all too easy to lose sight of more permanent losses.
In fact, the problem is even more complex than that. Before the Europeans
arrived, central Australia was subjected to several very large 鈥渟uperfloods鈥�
which left patterns of scour and soil deposition that still influence
vegetation growth. In time, weathering of these patterns creates natural
losses of vegetation and soil.
All of which is potential armour for the pastoral industry. Except that
now, the CSIRO researchers believe they have a way of pinning down the
degradation problem. Over the past few years, Geoff Pickup and his colleagues
at Alice Springs have developed a satellite-based method which they claim can
distinguish between temporary losses of vegetation cover and more permanent
losses caused by overgrazing and the trampling of thin soils.
The approach is based on a simple observation. In arid and semiarid areas,
the intensity of grazing and trampling increases towards water: large
herbivores can鈥檛 live off the nutrient-poor vegetation that dominates further
away from the centres of each fertile island. The result is a gradient in
vegetation cover that can be seen and monitored year on year by satellite
imaging. The key thing, however, is what happens during wet periods. If the
gradient vanishes, the vegetation loss is temporary and it is safe to assume
that the land鈥檚 capacity to respond to rainfall has been unaffected by
grazing. But the opposite is true if the gradient persists during wet
periods.
Big Brother
Suddenly, what was previously a blunt criticism flung at an entire industry
becomes something much sharper 鈥� a satellite-based method of exposing bad land
management which can be targeted to individual watering holes in individual
paddocks owned by individual farmers. To press that point home, Pickup and his
colleagues have already identified sites of overgrazing scattered through
paddocks in central and western Australia. Now they are waiting for the
inevitable controversy to flare up.
The idea of scientists using satellite technology to 鈥渟py鈥� on farmers, many
of them struggling to make a living, will invite the obvious references to Big
Brother. In the long run, it may also have financial implications. It鈥檚 an
open secret that Australian banks are seeking the advice of satellite
specialists to set up systems for valuing remote and vast farmlands. And these
days dealers in agricultural commodities regularly consult satellite images of
different parts of the globe. Indeed, farmers themselves may soon get in on
the act, buying satellite data in the hope of saving time and money monitoring
their land at ground level. Such services are already being offered by a
handful of start-up companies in Australia.
But if there is any controversy about the latest satellite data, it won鈥檛
end there. Grazing animals are not the only pressure on outback vegetation.
Rabbits also exact a painfully heavy toll. Couldn鈥檛 they alone have produced
the destructive habitat changes that are endangering so many mammals? And what
about other environmental pressures?
Morton is the first to admit that the demise of the outback mammals cannot,
in the end, be pinned to any one cause. The abandonment of Aboriginal fire
practices 鈥� the controlled burning of patches of land in a mosaic-like pattern
鈥� must have played some part (in the past animals could shelter in dense
unburnt patches while feeding off new shoots of grass in a neighbouring burnt
patch). As must the appetites of cats and foxes. But Morton believes that
without the introduced herbivores, those forces wouldn鈥檛 have had such a
devastating impact. Rabbits, cattle and native herbivores must all compete for
food in small patches of fertile land dotted in a vast infertile landscape 鈥�
and it鈥檚 the native mammals that come off worse.
But why only medium-sized mammals? Here we enter the realms of speculation,
but Morton points once again to the impact of an erratic climate on
vegetation. In droughts, the fertile patches shrink or temporarily disappear,
as may many of the smaller, scattered populations of native mammals;
conversely, when the rain comes, mammals crowded into drought refuge areas
will try to recolonise other sites. And there are reasons to think this ebb
and flow may affect medium-sized mammals the most.
It certainly wouldn鈥檛 bother the reptiles: their energy needs are tiny
compared with those of warm-blooded animals and, besides, most live off ant
and termite colonies in the infertile areas. Nor would it bother mammals
weighing less than about 50 grams. Most of these eat seeds or insects because
it is the only way they can maintain their body temperature: they are unlikely
to be wiped out by a loss of digestible grasses. Large herbivores, meanwhile,
benefit from being mobile enough to find a fertile patch even when the numbers
of such patches are plummeting.
But medium-sized mammals are caught between a rock and a hard place: they
need nutritious vegetation but can鈥檛 travel far. As a result, each drought
sees fewer and fewer refuges containing such mammals. For many species, says
Morton, the collapse has been rapid. And while some have fared better in other
areas of Australia, there is little point trying to reintroduce such species,
he argues, while the forces that drove them out are still in place in central
Australia.
The situation may seem desperate. But central Australia鈥檚 ecologists and
conservationists are not about to give up. They have redoubled their efforts
to develop ways of protecting land against soil erosion and other degrading
changes. They are investigating the pros and cons of farming soft-footed
kangaroos. They have freed areas of the national park that surrounds Ayers
Rock of rabbits and are working with Aboriginal communities to reintroduce
traditional fire practices.
All well and good, but where does all that leave the farmers? Must they
leave to make way for ecotourists? Not necessarily, say ecologists. The irony
is that the outback has taken so much of a battering that its flora and fauna
may now need human help to pull through to the next century. Who better to do
the job than the farmers?
Where there鈥檚 ants
Question: the most important animals in Australia are (a) marsupials (b)
monotremes (c) lizards. Most biologists would duck the issue, arguing that
notions of hierarchy have no place in ecology. But not Alan Andersen, an
entomologist with the CSIRO鈥檚 Division of Wildlife and Ecology in Darwin.
According to him the answer is none of the above. It鈥檚 ants.
Sceptics take heed. A single hectare of semiarid Australia ight contain 150
species. The combined mass of Australia鈥檚 ants exceeds that of all its
vertebrates. Ants scavenge. They eat and spread seed. They influence soil
structure with their nests and make a nourishing meal for lizards and other
insectivores. And in a land whose native fauna boasts few large herbivorous
mammals, all that adds up to a power over vegetation and ecology that ants in
other parts of the globe can but dream about.
But there is another reason for treating Australia鈥檚 ants with respect,
says Andersen: you can use them as 鈥渂ioindicators鈥�, as a quick and reliable
means to evaluate the health (or otherwise) of habitats. One reason for this
is that ant colonies can respond very quickly to environmental disturbances 鈥�
by for example withdrawing foragers and living off stores. But what also makes
ants useful is that they live everywhere, from wet tropics to degraded outback
deserts, and can be sampled and monitored with comparative ease. Small plastic
vials filled with ethanol solution (to act as a preservative) are all you need
in the way of traps.
Having trapped your ants like so many tea leaves in a cup, how do you read
off the fortunes of the ecosystem? Enter the entomologists. Andersen and
others have spent years studying how the numbers and types of ant communities
change as land recovers from various kinds of disturbance 鈥� degradation from
uranium mining, controlled burning of savanna grasslands, and so on. The key
thing is not necessarily to name individual species, says Andersen (many have
never been characterised). It鈥檚 to classify the 鈥渆cological behaviours鈥� of the
ants.
Regular, controlled burning of tropical dry forests in northern Australia,
for example, favours 鈥淚ridomyrmex鈥� ants, aggressive, competitive species which
prefer open habitats and have highly specialised food gathering strategies.
But after hotter wildfires in southern Australia, opportunist ant species
dominate as the land recovers. These are the 鈥渆psilons鈥� of the ant world. They
have no specialised foraging and predatory behaviours and in healthy habitats
lose out to Iridomyrmex species. Opportunist ants are unusually the hallmark
of a disturbed ecosystem.
Take the case of uranium mining. When Andersen monitored ants at a series
of mining sites 鈥渞evegetating鈥� near Kakadu, he found that each one was
dominated by a succession of ant communities. First on the scene were
Iridomyrmex species. But as plant cover increased, these were replaced by
opportunist species. At some sites, moreover, the number of species climbed
initally but then stalled. The problem? Most of the mining sites were being
monopolised by acacia shrubs. Andersen discovered that controlled burning was
necessary to break that monopoly and let in eucalypts, other types of
vegetation 鈥� and more ant species.
It will be a while before such studies can be translated into a guide for
鈥渞eading鈥� ant communnities in Australia. But there are already signs that the
more ant species there are in a recovering habitat, the more species of
mammals, plant and reptiles you are likely to find.