In The New Nature, Australian ecologist Tim Low takes us on a tour of his continent/country to make the point that every nook and cranny has been impacted by the activities of humans. (1) It is a dizzying adventure because it challenges many of our assumptions about nature:
- Human civilization has benefited many plant and animal species in Australia. For example, places such as garbage dumps and sewage treatment plants are sources of food for many species, from the bottom of the food web to the top. Many animals hang out in the company of humans where they find housing, food, and protection from their predators.
- However, there are “winners” and “losers” in the changed environment. Not all species benefit equally from the resources provided by humans and not all species are equally adaptable to change.
- When “winners” dominate at the expense of rare species, the “winners” are nearly always native species, according to Low. Non-native “invaders” are hardly mentioned in Low’s tour of Australia.
- Low defines “conservation” as active management of ecosystems, including aggressive culling (AKA killing) of native species as needed to prevent extinction of rare species. He acknowledges that these massive killings are controversial in Australia, which was some comfort to us.
- Eucalyptus forests in Australia are in serious trouble. There is no evidence in Australia that they are the aggressive “invaders” they are labeled in California.
As ecologists tend to do in the United States, Low uses pre-European Australia as the baseline from which changes in ecosystems are judged. The Aborigines of Australia were hunter/gatherers, like many Native American tribes in North America. Like our Native Americans, they used fire to support their hunting. Periodic burning of grassland promotes the growth of new grass which attracts the grazing animals they hunted. In Australia, the grazing animals were marsupials, such as kangaroos, rather than the ungulates in North America. Periodic burning also prevented natural succession from grassland to forests.
When Europeans arrived, the population of Aborigines plummeted as it did in North America and the remaining population was displaced from most of their homelands. Their way of life was radically altered and hunting was no longer their primary means of living. That was the end of the annual grassland fires that had maintained the grassland.
The Europeans brought sheep and cattle that partially replaced the function of the Aboriginal fires to maintain grassland. However, there is a fine line between over-grazing and grassland maintenance. Many native grasses were replaced by annual grasses introduced with the livestock of the Europeans, just as it was in North America. Europeans in Australia actively suppressed fire for safety reasons.
Here is a brief summary of the consequences of these changes in human use of the land:
There were few koala bears in Australia when Europeans arrived at the end of the 18th century. They were easy marks for Aboriginal hunters because they sleep in the canopy of trees during the day. When Aboriginal hunting stopped, the population of koalas skyrocketed. Because they are so cute, humans love them and they want them everywhere, so they have been introduced into parks where they had not lived in the past. Now they are killing eucalyptus forests in those parks. Park managers want to cull them and sometimes they do, but Australians strenuously object to these efforts to balance the population of koalas with available resources. When managers are prevented from culling, the forests die and the koalas eventually starve. This makes for disturbing reading.
Kangaroo populations have benefited from both the disappearance of Aboriginal hunters and the eradication of dingoes by cattle and sheep ranchers. The large species of kangaroos now have no natural predators so their populations have destroyed much of the grassland that they graze. Kangaroos are also aggressively culled and Australians aren’t happy about that either.
- Insect predators of eucalyptus forests have increased because they are “fed” by the fertilizer in stock paddocks.
- The absence of fire has also radically altered many ecosystems. Where kangaroos and stock have overgrazed, the fires that start aren’t sustained because there isn’t sufficient fuel. When there are no fires to reduce the understory, the forest retains more moisture. The forest gradually converts from dry forests to tropical forests and the trees cannot regenerate in the wet, dense understory: “If you take eucalypt forest, add fertilizer and water, you have the recipe for rainforest.” This is another factor in the decline of the eucalyptus forest in Australia.
- The changes in these ecosystems reverberate throughout the food web. The insects, birds, and animals that lived in one type of ecosystem aren’t necessarily adapted to the changes. Some species disappear and others arrive that often compete with their predecessors in the ecosystem, further diminishing rare species.
Although there are North American counterparts to most of these changes in the environment, the concluding chapters of Low’s remarkable book are entirely foreign to us. He is unequivocal in his assessment that human attempts to compensate for the damage that has been done to Australian ecosystems in their residential gardens inflicts even greater damage by helping “winners” displace “losers.” Bird boxes and feeders benefit only the most aggressive birds which give them an even greater advantage over the forest birds that are in decline. Likewise, garden ponds are occupied by only a few species of the toughest frogs. His assessment of native plant gardening is so surprising that we will quote it directly:
“One tenet of wildlife-friendly gardening is that native plants be used, but often that’s not what animals want. Growing native plumbago for native butterflies doesn’t help as much as growing the exotic equivalent, which sprouts hundreds more flowers. And switching native animals over to native plants is often harder than it sounds.”
We visited Australia as tourists for a month, but that is nearly the limit of our understanding of its ecology. It felt much like home inasmuch as it’s another of the five Mediterranean climates in the world. We can’t claim that this experience is sufficient to question Tim Low’s description of Australian ecology. So, until we learn otherwise, we must say that the drivers of environmental change in Australia are primarily anthropogenic and the existence of non-native species plays little role. However, we can’t help but wonder if a difference of perception accounts for the radically different assessment of American ecologists. In other words, are American ecologists blaming non-native species for environmental changes that are just the consequence of human activities? That seems another equally logical explanation for the radical difference in American and Australian assessments of non-native species.
(1) Tim Low, The New Nature: Winners and Losers in Wild Australia, Penguin Books Australia, 2002