How heat waves distort ecosystems (the lasting legacy of a temperature peak) – High Country News – Know the West


After the Northwest “thermal dome” this summer, scientists are looking for signs of ecological ruin – or resilience.

  • A bed of kelp on San Juan Island photographed a month before the Heated Dome.

    Courtesy of Robin Fales

  • A bed of kelp on San Juan Island pictured on the second day of the Heated Dome.

    Courtesy of Robin Fales

  • A bed of kelp on San Juan Island photographed on Day 4 of the Heated Dome.

    Courtesy of Robin Fales

  • A bed of kelp on San Juan Island photographed on Day 10 of the Heated Dome.

    Courtesy of Robin Fales

During this summer A sweltering heat wave, Robin Fales patrolled the same shore on San Juan Island in Washington every day at low tide. The stench of decaying marine life increased as temperatures hit triple digits – about 30 degrees above average – and Fales watched the kelp beds she studies wither and wither. “They were bleaching more than I had ever seen,” recalls Fales, a PhD. candidate and marine ecologist at the University of Washington. She didn’t know if they would make it.

Never in recorded history has the Pacific Northwest experienced anything like the “heat dome” that quelled the region at the end of June 2021. Temperatures reached 116 degrees Fahrenheit in Portland, Oregon, and 121 degrees at Lytton, British Columbia – the highest on record north of the 45th parallel.

Scientists said the event would have been “virtually impossible” without climate change. It has killed hundreds of people, damaged roads and power lines, and devastated crops. It has also caused widespread ecological fallout, the full extent of which scientists have yet to grasp.

Early reports were sobering: a billion shellfish and other intertidal animals cooked to death on the British Columbia coast. The Portland Audubon Society declared a “hawkpocalypse” because it cared for dozens of sick and injured birds. And in eastern Oregon, state officials estimated tens of thousands of sculpins, a seabed fish, perished in already drought-strangled waterways.

Bleached kelp on San Juan Island, Wash. During this summer’s dome heat.

Courtesy of Robin Fales

“They were whitening more than I had ever seen.”

By the fall, headlines and memories had faded, but the effects of the heatwave linger. In fact, researchers have learned that short periods of high temperatures can pose a greater threat to plants and animals than long-term warming, and may even increase the risk of extinction.

In a recent study, researchers looked at 538 species from around the world, nearly half of which had already gone extinct in at least one place. They found that condemned populations experienced larger (and faster) increases in annual maximum temperature than others. Surprisingly, however, they often experienced smaller average temperature changes, said John Wiens, an evolutionary ecologist at the University of Arizona and co-author of the study. “The most important variable is these hottest summer temperatures.”

Extreme heat can kill organisms, especially if they are also exposed to intense sunlight. Dehydration sets in and organs fail as enzymes stop working and proteins are damaged. Trauma can make survivors more vulnerable to disease and predation, and reduce or delay reproduction. Hot weather can also cost animals dearly by discouraging them from foraging or hunting. And these events are happening more often: By 2040, heat waves are expected to become 12 times more frequent than in a world that is not warming.

After the last episode in the Pacific Northwest, researchers began tracking damage to a variety of species and ecosystems, such as coastal forests, which were doing particularly poorly. The burnt leaves were turning sickly orange tones on the hillsides, and the trees already stressed by the drought let their needles drop prematurely. But the deadliest impacts may be invisible, said Christine Buhl, entomologist in the Oregon Department of Forestry: Thirsty trees, for example, may have suffered damage to their roots and vascular systems if they could not. not extract enough moisture from the soil. “We will know in the years to come how bad it was,” said Buhl.

“You can still shop around and find the legacy of this event.”

Australia provides a grim overview. After a series of heat waves that hit the west of the country in 2010 and 2011, scientists documented widespread tree death, among other impacts, which then contributed to beetle outbreaks and forest fires, a said Joe Fontaine, fire ecologist at Murdoch University in Perth. Even now, he said, “you can still go around and find the legacy of this event.”

Yet heat waves can also help species adapt to long-term warming by causing rapid evolutionary changes, said Lauren Buckley, climate change ecologist at the University of Washington. They can eliminate unfit individuals, giving an advantage to those who tolerate warmer temperatures. Scientists have seen evidence of such changes in Douglas-fir and fruit fly populations. But “there is a kind of trade-off,” Buckley said, between a stress test and a slaughter.

It is too early to know if the recent peak in temperature has reached the sweet spot for some species, if any, from the Northwest. On San Juan Island, however, Fales has regained some hope. After the heat wave, Fales examined the damage to the kelp she is studying and determined that even though it had lost about half of its biomass, most of the plants were still alive. Many mussels have also survived.

Perhaps that’s because the warm spring temperatures prompted them to build up defenses before the heat wave, Fales said, by producing heat shock proteins that repair other damaged proteins, for example. But there is another possible factor: By celestial coincidence, summer low tides on the island always occur at midday, exposing intertidal organisms to maximum temperatures and making it “a hot spot,” Fales said. . Maybe the kelp and its neighbors had already started to adapt.

Kelp beds are exposed at low tide along the Oregon coast. Kelp and other organisms were put through a stress test during this summer’s “heat dome”.

Bazzano Photography / Alamy

Julia Rosen is a freelance science and environment journalist in Portland, Oregon.

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