Environmental Engineering Reference
In-Depth Information
CHAPTER 6
ECOLOGICAL CLEANSING
Many conservationists see themselves as engaged in a war against alien species. To protect natural
ecosystems, the outsiders must be shot, poisoned, burned, hunted by dogs, uprooted, chainsawed, or
gobbled up by specially introduced insects. Many make their cases on grounds of protecting some vital
national resource, whether crops or forests or water supplies. There can be no compromises. No talk
of animal rights. Not even any regard for the local biodiversity that might be lost as the foreigners are
removed. All methods are acceptable in the battle to purify encroached ecosystems and re-create the
pristine. Because aliens are bad, and natives are good.
Few countries have gone on the offensive against alien species with the zeal of post-apartheid South
Africa. It has deployed more than twenty-five thousand people every year for almost two decades to rip
up whole landscapes and root out sixty-eight species of alien trees, most of them planted during colonial
and apartheid times.
1
The foreign trees are, says the head of the program, Guy Preston, “analogous to a
cancer” in the country.
2
The rhetoric suggests a desire to purge the legacy of foreign species along with
that of foreign occupation and apartheid politics. But has the rhetoric got in the way of practical policy
and good science? Why are there more invasive species than ever across the veldt?
European settlers brought in a range of exotic trees in the late-nineteenth century to, as they saw it,
“improve” the land and make the bare grasslands look more like home. Back then, the trees were re-
garded as superior to native species, because they were faster-growing and said to be beneficial to the
wider environment. An Australian acacia called black wattle (
Acacia mearnsii
), for instance, stabilized
sand dunes while producing charcoal, firewood, tannin for the leather industry, and timber to shore up
shafts in gold mines. But the foreign trees often spread to places they were not wanted, in particular
invading farmland. Government officials today claim that fifty million acres of the country have been
covered by foreign acacia, pines, eucalyptus, mesquite, prickly pear, water hyacinth, giant reeds, and
others. The official policy is that they have to be removed.
The purge has been masterminded in part by ecologists fearful of foreign trees invading the fynbos
district in the Cape region. This is one of the most biodiverse spots on the planet, with more than eight
thousand species of plants, two-thirds of them found nowhere else. The ecologists' pitch to the South
African government has been that the alien species could pose a threat to water supplies. Researchers
claim that around 7 percent of the nation's rainfall is taken by foreign trees. In the future, they could
increase their take by a third around water-scarce cities such as Cape Town.
3
In a country where only 10
percent of rainfall makes it into its parched and seasonal rivers, there is understandable alarm. Willem
de Lange and Brian van Wilgen of the Centre for Invasion Biology in Stellenbosch estimate that the
water loss translates to an economic loss to the nation of around half a billion US dollars each year. Con-
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