Continual Wildfires, Greater Heat/Drought Extremes Mean Forests May Be Unable To Regenerate
Pungent and damp, the so-called tall, wet forests of southeastern Australia are home to the tallest flowering plants on Earth. Eucalyptus regnans, the Latin name of the mountain ash, means “ruler of the gum trees”—which is fitting, given these giants can reach more than 300 feet high. Many of Australia’s gum trees, particularly those in drier forest types, are famously able to tolerate fire, throwing out new buds and shoots within weeks of being engulfed in flames. But even these tenacious species have their limits.
Old-growth forests of the mountain ash and a related species, the alpine ash, are among the gum trees that are less tolerant of intense blazes. In the state of Victoria, these trees had already been severely depleted by logging and land clearing. Now, the bushfires that have burned more than 26 million acres of eastern Australia in recent months are putting the forests at even greater risk.
Some of the forests razed this year have experienced four bushfires in the past 25 years, meaning they’ve had no chance to recover, says David Lindenmayer, an ecologist at the Australian National University in Canberra. “They should be burning no more than every 75 to 125 years, so that’s just an extraordinary change to fire regimes,” he says. “Mountain ash need to be about 15 to 30 years old before they can produce viable amounts of seed to replace themselves following fire.” The loss of these dominant trees is a significant problem, since they provide vital habitat for threatened animal species such as the sooty owl, the giant burrowing frog, and a fluffy arboreal marsupial called the greater glider. (Also find out how Australia’s fires can create big problems for freshwater supplies.)
“The ecosystem has effectively collapsed, it’s transitioned into something else … more likely to be colonized by generalist, weedy plants,” says John Woinarski, a conservation biologist at Charles Darwin University in Australia’s Northern Territory. “They’ll converge into less interesting, less distinctive vegetation that supports fewer threatened plants and animals.” As the world warms with climate change, the situation in Australia reflects what’s happening in forests globally—from California and Canada to Brazil and Borneo. Even forests made up of species that thrive on cycles of fire and regrowth are losing resilience in the face of wildfires that are escalating in frequency, severity, and extent. According to research published earlier this month, climate change is significantly increasing the risk of wildfires by stimulating hot and dry conditions and high-risk weather. Over the past 40 years, the length of fire seasons has increased by 20 percent across more than a quarter of the world’s vegetated land surface.
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https://www.nationalgeographic.com/science/2020/01/extreme-wildfires-reshaping-forests-worldwide-recovery-australia-climate/
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