Greening the Desert - Feral: Rewilding the Land, the Sea, and Human Life - page 88

monsters. Among them was a spiny anteater the size of a pig; a giant
herbivore a bit like a wombat, which weighed two tonnes; a marsupial
tapir as big as a horse; a ten-foot kangaroo; a marsupial lion with
opposable thumbs and a stronger bite than any other known mammal,
which could prop itself up on its tail in order to stand on its hindlegs
and slash with its tremendous claws; a horned tortoise eight feet long;
a monitor lizard much bigger than the Nile crocodile. Most of these
species, alongside many other marvellous beasts, disappeared between
40,000 and 50,000 years ago. At roughly the same time, the dense rain-
forests which covered much of that continent began to be replaced with
the grass and scrubby trees which populate much of the outback today.
Two debates have raged among ecologists. Were these shifts caused
by natural climate change or by humans? If, as now seems probable,
they were caused by humans, were the extinctions of the giant animals
the result of hunting or of the destruction of their habitats? Research
published in the journal Science strongly suggests that humans hunted
the large animals to extinction, and that the disappearance of the large
animals then caused the destruction of the rainforests. 52
Analysing the pollen and charcoal in cores taken from an ancient
lake bed, and using the fungus that grows on the dung of large herb-
ivores to measure their abundance, the researchers showed that the shift
from rainforest to dry forest took place some 10,000 years before the
climate dried out. Both the mass extinction and the change in habitat
happened while the climate was stable. They also showed that fire
began raging through the rainforests around a century after the large
mammal populations collapsed; and that grass and scrub replaced the
forests two or three centuries later. When the giant herbivores disap-
peared, they suggest, the twigs and leaves that would otherwise have
been browsed began to build up on the forest floor, creating a fuel
supply that allowed wildfires to destroy the rainforests and catalyse
the shift to grass and scrub. The herbivorous monsters of Australia,
like the mammoths and musk oxen of Beringia, appear to have sus-
tained the ecosystem they browsed.
One of the interesting implications of the discovery of widespread
trophic cascades is that removing an animal from a system - espe-
cially a top predator - may have counterintuitive and destructive
results. For example, in many parts of Africa, people have killed lions