"The life cycles of many plants and animals that occur in these fire-prone ecosystems are intimately attuned to certain kinds of fire regimes," he said. "For example, the seeds of some plant species don't germinate substantially in the absence of fire."
Intense wildfires also kill fungal pathogens in the soil and parasitic plants, such as mistletoe, and stimulate the release of nutrients into the soil.
"In a way, high-intensity fire can cleanse the environment," Whelan added.
Within weeks of a wildfire, multitudes of green and pink shoots appear from charred eucalypt trunks and blackened earth. The Australian bush returns reinvigorated like a phoenix from the ashes.
Threat to Biodiversity
The rapid spread of urban development into areas of native forest has increased the risks to human life and property from wildfire. Houses built among the trees make the task of controlling fires more difficult. In these areas, more hazard-reduction burns are being carried out, and they are affecting more land.
But as scientists have discovered, frequent fires have adverse effects on an ecosystem.
"In terms of biodiversity, the popular image is that the damage is done when everything goes black [after a wildfire]," said Keith. "But to me, the real ecological impact is something more insidious. We don't see it happening obviously, but when you compare the vegetation with what was there before a series of fires, the change can be quite astonishing."
In many Australian plants, the mature individuals are killed by fire, and the species regenerates after fire entirely from seeds.
Plants that are both slow growing and depend entirely on seeds to regenerate after fire are particularly vulnerable. If such a plant burns before it has a chance to mature it can't produce seeds.
"The chink in their armor is the juvenile period," said Whelan. "This ranges from three to ten years in vegetation in the Sydney region, so if there are two to three fires close together, this can lead to local extinctions."
Frequent fire also changes the understory of the forest, eliminating shrubs and leading to more open patches of grasses and annual herbs.
"The nature of the understory of the forest is really different if it's burnt frequently," Whelan said.
Many animals, such as the endangered long-footed potoroo, a small relative of kangaroos, depend on thick understory to provide nesting sites, food, and protection from predators.
Sharing the Landscape
Government agencies in New South Wales, the most populous eastern state, are working to balance these competing needs.
Too-frequent fires have been listed on the NSW Threatened Species Conservation Act as a significant risk to 14 animal and 40 plant species.
In August this year, the NSW government introduced legislation requiring local councils to map bushfire-prone land. The legislation also calls for stricter regulation of building materials used in these areas, and increased consideration of biodiversity when carrying out prescribed burns.
Hazard-reduction burns look unimportant compared to an almighty firestorm, but their cumulative impact on the environment may be just as profound, say the researchers.
After all the phoenix of legend only rose from the ashes once every 500 years. Can we expect Australian forests to do it every year?
Join the National Geographic Society
Join the world's largest nonprofit scientific and educational organization, and help further our mission to increase and diffuse knowledge of the world and all that is in it. Membership dues are used to fund exploration and educational projects and members also receive 12 annual issues of the Society's official journal, National Geographic. Click here for details of our latest subscription offer: Go>>
|
SOURCES AND RELATED WEB SITES
|
