After the fire, the long return to life of nature in Australia

Mis à jour : mars 1

In this country ravaged in recent months, fire prevention is crucial if nature is to have time to recover.

The huge conflagration that has gripped Australia in recent months has already revealed a disastrous record, which will no doubt continue to worsen. Ten million hectares went up in smoke, killing at least 29 people. According to simulations by Christopher Dickman of the University of Sydney and Andrew Beattie of Macquarie University (Sydney), about a billion animals also died in the fires.

L’homme pourra-t-il « réparer la nature » ? Autrement dit, reconstruire le biotope et les différents écosystèmes, permettre au « vivant » de se relever ? Vaste question à laquelle probablement aucun écologue ne peut répondre de façon certaine. Mais une chose est sûre : dans ce pays grand comme 14 fois la France, le climat est naturellement aride et la végétation y est adaptée, même sur la côte est.

"The bush lives with fire"

"The Australian bush and natural forests are ecosystems that live with fire, are adapted to fire, and even need it, albeit at a certain rate, to regenerate," explains Eric Rigolot, a forest ecologist at INRAE, the National Institute for Agricultural Research and the Environment. "This is a peculiarity that can be found in the Mediterranean, but it is difficult to imagine for an inhabitant of a temperate climate. "As a result, these regions must be particularly well maintained in terms of brush clearing by means of "controlled burning" in winter. The houses, moreover, should not be too scattered.

"The best way to reconstitute the plant cover in South-East Australia is to let nature take its course: natural or spontaneous regeneration is still, barring exceptions, the best way," says Jean-Luc Dupuy, a fire physicist at Inrae. This is what we do in France, in the Mediterranean area. The principle: leave things in place and don't touch anything. Leave the charred trunks, cut them only if there is a risk of erosion, on sloping ground for example, and turn them into fascines, branch assemblies, to retain the earth. With a nuance, according to the physicist: "In the eucalyptus forests selected for pulp production, Australians could resort, on a small scale, to replanting.

Given the high risk of such mega-fires, one can also imagine favouring less or less combustible tree species - deciduous rather than coniferous, trees with thicker bark, no low branches, and a high perched crown. Although Australia is the native continent of the 800 species of eucalyptus (95% of natural forests), rich in highly flammable volatile substances, "we can also reduce their numbers, like the Portuguese who, after the catastrophic fires that killed more than 100 people in 2017, eliminated them," Jean-Luc Dupuy points out.

Encouraging endemic species, limiting invasive species

The wildlife is a different matter. Australia's repopulation is likely to vary greatly between regions and sites - whether we are talking about small invertebrates, birds or mammals. In some places it takes time for grass, waterholes, herbivores and then carnivorous predators to reappear; in others, such as northeast Queensland, grass grows back within a few days, as soon as it rains.

In Australia, wildlife is different from other continents for two reasons," says François Moutou of the French Society for the Study and Protection of Mammals. Firstly, it is home to many endemic species (93% of amphibians, 83% of mammals, etc.)," such as koala, kangaroos, platypus, echidna, possums, etc. "In Australia, wildlife is different from other continents for two reasons," says François Moutou of the French Society for the Study and Protection of Mammals. "Then, the naturalist continues, it has been colonized by man by many exotic and invasive species. "The most common are rabbits, cats, foxes and dingoes (domestic dogs returned to the wild).

These specificities complicate the situation: naturalists will have to encourage the expansion of endemic species by limiting - or even eradicating - certain invasive species. This was the case with the slaughter of 10,000 wild dromedaries in a South Australian desert, which, thirsty, threatened the Aborigines.

Experience from Mozambique

"In this post-fire context, when in some places the ground is still smoking, it is a little early to know exactly what to do about the recolonisation of ecosystems," observes Johan Pansu, a post-doctoral student in ecology, currently at CSIRO (the equivalent of the CNRS) in Sydney. Ecologists need to take stock of the situation using satellite, aerial and UAV images. Surveys are then validated by field staff, including federal and national park managers, who inventory and locate "islands of green", surviving animals, and dead animals. It's a long-term job. "The most important criterion is the quality of the habitat, the biotope," says Johan Pansu.

Thus, restoring animal populations only makes sense once the habitat has been rehabilitated. But other questions remain: what is the balance between herbivores and predators? Should we restore an environment that is perfectly similar to the one that disappeared? In this respect, the experience of Mozambique provides valuable lessons. The re-establishment of animal populations - elephants, buffalo, hippopotamuses, antelopes - in the bush after the civil war (1977-1992, Editor's note), with its attendant misdeeds such as trafficking, led to a different balance," explains Johan Pansu. We saw the installation of a majority of medium-sized antelopes, and among them, a dominant species. This is probably due to the order of reintroduction and the speed of reproduction of the species. »

However, man is still far from controlling the floral and wildlife repopulation of the large burned areas. In arid zones, but also in California, Amazonia or Europe, we will have to live with the flames. Already in 2001, Stephen J. Pyne, an environmental historian at the University of Arizona, believed that we were entering the "Pyrocene", the age of fire.

Ideas on the table

Australian (Conservative) Prime Minister Scott Morrison has decided to set up a national agency to finance reconstruction, but no further details are available at present. It should be endowed with 1.2 billion euros, according to The Guardian Australia.

Beyond that, Australia has to anticipate a probable increase in the pace and intensity of fires and therefore plan its vast territory according to the new climatic conditions. Some regions could thus become uninhabitable.

Traduction from the article of Lacroix, written by Denis Sergent (February 2020) :


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