The combination of warming, drought and wildfire could turn Yellowstone's forests into grassland by the middle of the century, scientists warn.

Wildfires are a normal occurrence in most forests in the American West. Large fires are less common. In Yellowstone, big blazes rip through the park once every 100 to 300 years. Flora and fauna in Yellowstone are adapted to periodic large fires, but they need time to recover and regenerate.

But according to a new study, large fires are becoming more common, and hotter, drier conditions are making it more difficult for plant and animal species to repopulate ecosystems scorched by wildfire.

As prolonged droughts, extreme heatwaves and bigger fires become the new norm, scientists worry Yellowstone's forests will be grassland in just a few decades.

"It's terrifying in some ways. We are not talking many years away," Monica Turner, professor of integrative biology at the University of Wisconsin, said in a news release. "Today's college students will be mid-career. It feels like the future is coming at us fast."

As a number of studies have shown, hot, dry conditions are driving an increase in the frequency and severity of wildfires in California. The trend is expected to continue as the planet warms.

To better understand how trees will fare under hotter, drier, fire-prone conditions, scientists planted and observed the development of tree seedlings at several test sites in Yellowstone. Turner and research partner Winslow Hansen located grow sites with hotter, drier conditions, including areas of forests recently burned. The duo monitored the seedlings for three years.

At lower elevations where temperatures were higher, the majority of Douglas fir and lodgepole pine seedlings failed to establish, and those that did died within three years. More seedlings survived and matured at higher elevations where temperatures were cooler.

Researchers published the results of their study this week in the journal Ecological Monographs.

"It wasn't just a small reduction," said Turner, "it was a failure to establish at the lower elevations."

Follow up studies in the lab using soil collected from a range of Yellowstone sites showed soil temperature by mid-century are likely to be too high to support tree regeneration in the wake of larger fires.

"Forests are critical from both social and ecological perspectives," Hansen said. "The Greater Yellowstone region may be a very different place to live and visit over the next few decades."

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Water, not temperature, limits global forest growth as climate warms
Tucson AZ (SPX) Jan 18, 2019
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