From Water Deeply (Jane Braxton Little):

New research into how drought kills trees has helped reveal a potentially huge climate consequence of an increase in dead and dying forests that one scientist cautioned could result in a “carbon death spiral.”

[…]

“If we understand the mechanisms of how trees die, we can make predictions and prioritize areas for management,” he said.

First we need to understand how healthy trees function. They get water from the soil, pulling it up through their roots through xylem, one of two specialized transportation tissues in vascular plants. The water flows into tree trunks and branches to leaves or needles. Sunlight turns the nutrients in water to sugar and sap, which nourish new growth.

When there is less water in the soil, trees pull harder. When they pull too hard they break the column of water in the xylem, creating air bubbles known as embolisms. This causes “hydraulic failure.” And this is what killed all of the trees studied by the research team of 62 scientists, said Adams.

But another process also causes trees to die when their response to drought deprives them of carbon.

“Trees aren’t stupid,” Adams said. To prevent losing precious water to the atmosphere through their needles and leaves, trees close the pores scientists call stomata. That keeps the water in the tree, but stomata do more than prevent water loss. They also let carbon dioxide in, allowing trees to carry out photosynthesis.

When trees close their stomata to wait out a drought, they are no longer making any food through photosynthesis. Instead, they are relying on stored sugars and starches. If the drought lasts long enough, they use up everything they have stored, and they die.

Carbon starvation contributed to tree mortality in at least 60 percent of the cases the researchers studied. They still don’t understand the critical threshold for carbon starvation but know it plays a significant role in trees dying.

Scientists also know bark beetles contribute to tree mortality. That sticky resinous sap used to pitch out beetles is made from carbon. When trees become carbon-starved they are not only unable to metabolize the nutrients for survival; they are also unable to muster the carbon they need to defend themselves against beetles.

The connection between physiological stress caused by drought and defending against bark beetle attack is still an active area of research, Adams said. Entomologists have tended to approach tree mortality in the West through beetles, while physiologists have come at it from the drought perspective…

He and his colleagues analyzed drought-induced mortality in 26 tree species. They examined data from 19 recent experimental and observational studies from around the globe. The research will help scientists and land managers more accurately predict how trees will respond to environmental stresses that include insect damage and disease as well as drought, said Lina Patino, a section head at the National Science Foundation’s Division of Earth Sciences, which cofunded the study.

From The Mountain Town News (Allen Best):

Like millions of other Americans, I drove hours to dawdle in the brief darkness of the solar eclipse. Spreading our blanket along a highway in the rolling prairie of Nebraska, my companion and I were surrounded by people from Texas, Iowa and Colorado.

Across the barbed-wired fence was a ranch family, three generations of Nebraska red under the blue sky, marveling to see so many people along their lonely country road. One car an hour was the norm, said the patriarch. We talked like old neighbors, us city folks drawn from across the continent’s midsection and our country cousins we had never met. We were uniformly of good cheer. Did we vote the same last November? I doubt it, but it did not come up at this convergence of harmony.

Then darkness came, cold and quiet. Crickets chirped and Angus cows and calves bawled into the twilight. We shivered in this spectacle on the dark side of the moon, halfway expecting angels to begin dancing about. Then the light returned.

Science had predicted all this with precision. None of us gathered along the barbed wire fences in Nebraska had doubted it. President Donald Trump did not dismiss it as a Chinese hoax.

But why so little faith in climate science? If the precise increase in temperatures and extent of weather extremes remains uncertain, it’s clear that our path is fraught with risk.

Three days later, Colorado’s two senators, Cory Gardner and Michael Bennet, spoke at a Colorado Oil and Gas Association conference. They sit on opposite sides of the political fence, but in Denver they sat together in stuffed chairs to brag, as best they could, about their bipartisan efforts before a crowd clearly tired of the twitter storm in Washington D.C. But one looked over his shoulder when talking about climate change, and one looked straight ahead.

Bennet, a Democrat, has a deep background in fossil fuels. Early in his career, he was up to his elbows in oil and gas as a lieutenant for the billionaire Phil Anschutz. As a senator, Bennet bucked the environmental community in voting to authorize the Keystone XL pipeline. But this year he has been bearing down on climate change.

“As I travel Colorado, people are increasingly worried about climate,” he said. “The effect it is having on their farms and ranches, on their ski areas, and on the national forests.” He told the drillers that they will need to engage in a “constructive conversation” about climate change, because the reality “is just not going to go away.” Better for the United States to figure out the answers than another nation, he added in his own version of make America great.

Gardner, though, is the more important individual in this conversation. He’s a Republican from a town of 3,600 on the Great Plains, He doesn’t deny climate science. Occasionally he’s capable of backbone. After Charlottesville, he immediately issued a statement condemning the racism and white nationalism. At a town hall several days later, he even managed smiles while confronting one infuriated question after another about his effort to dismantle Obamacare. The Resistance can be as nasty as the Tea Party.

But in Denver, Gardner recited tired arguments recycled more times than Seinfeld reruns. He pointed out—accurately—that as a Colorado state legislator he had supported renewable energy that benefited his rural constituents. Then, like an ancient fearing the darkness of an eclipse, he warned of the unbearable costs of renewable energy to people of fixed incomes or on farmers irrigating corn and alfalfa fields. “You don’t have to go so far as to cause economic collapse,” he said.

The argument is absurd. Utilities have been scrambling to get their electrical wires around wind and solar. The Public Service Co. of Colorado on Tuesday announced ambitions to shut down two older coal-fired plants. It’s cheaper for consumers, explained PSCo president David Eves. Our technology has advanced.

Residential customers of Aspen Electric—yes, the ski resort favored by Trumps and other billionaires—got their electricity for 26 percent less in January than the farmers around Gardner’s home-town. Towns and cities can be serviced more cheaply than scattered farms. But Aspen now has 100 percent renewables; farmers remain heavily reliant on coal generation.

Scientists had the eclipse down pat. Unfortunately, they’re probably right about climate change. It will take somebody like Gardner, with the same backbone he did after Charlottesville, to clip that barbed wire fence that has made climate change a partisan issue.