Dying California forests offer a glimpse into climate change

This article about the damage to California forests from global warming has been blocked by Facebook because of someone complaining it contains "abusive language", which is nonsense. An example of how the power elite shapes our news. When Facebook people have time to look at it, I'm sure it will be unblocked. But that can take awhile.

http://www.cbc.ca/news/technology/dying-california-forests-offer-a-glimpse-into-climate-change-1.3187672

By Kim Brunhuber, CBC News Posted: Aug 13, 2015

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Every year over the last decade and a half, the U.S. Geological Survey has descended on Yosemite and Sequoia National Parks in California to give 17,000 trees a physical. But in a growing number of cases, what's starting off as a check-up is turning into an autopsy.

The cause of death is usually insects or fungus, but researchers suspect it's almost always because of one culprit: lack of water.

Normally, only about two per cent of the trees in their study areas die. But this year, that number has grown to 13 per cent.

"That's a really severe uptick," says U.S. Geological Survey ecologist Nate Stephenson. "We've never seen anything like it before."

Stevenson bends the branch of an incense cedar. Most branches are covered with dry, dead orange needles. The rest are bare.

"I used to call them 'the immortals,' because they just never seemed to die," he says. "In the fourth year of drought, they've started dying by the bucket-loads. So they're no longer the immortals."

Stevenson has surveyed some of the oldest, richest forests in the U.S. and British Columbia. Compared to just a few decades ago, he found that the trees' death rate has doubled from one to two percent. It may not sound like a lot, he says, but he says imagine if you were talking about your hometown.
[And surely the number of new trees has decreased in the drought. So the equilibrium between trees dying and new trees would be broken, with the total number decreasing.]

"If you looked back and saw that death rates had doubled, you'd really wonder what was going on," Stevenson says. "The one thing that really stood out is warming temperatures. We think that's what's driving the increase in tree death rates."

For the past four years, California has been going through a record-setting drought. In January, the state's governor, Jerry Brown, declared a state of emergency.

In June, Naomi Tague of UC Santa Barbara published a study in the journal New Phytologist on die-off in California forests that found that 12 million trees died due to drought this year alone. Tague, who is Canadian, says the hot, dry weather has been great for the insects and bad for the trees.
[Insects are more active in hot weather, up to a point. As long as the trees are still alive, the insects can get moisture from eating them. Also, plants have defenses against insects, and surely those defenses are weakened by the drought. For sure, in a drought plants would be less able to grow new leaves to replace those eaten by insects.]

While the situation in California is dire now, in the future, Canadian forests may be at greater risk, even if the drought is less severe.

"The trees [in California] are used to drought, and so you have to get this severe drought before you start to see this die-back," Tague says.

"But you can imagine that a spruce forest in the boreal part of Canada, it's not used to seeing drought. So it hasn't developed the same types of defensive mechanisms to insects."

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"The increase in temperature is greater at greater latitudes," Tague says. "A cold drought is not the same as a warm drought."

Their research has found that no tree seems to be immune, including the toughest, most drought-resistant trees in this forest: giant sequoias.

Some of the trees in Sequoia National Park were a thousand years old when Julius Caesar crossed the Rubicon. Last year, Stevenson spent a few days crawling around the forest floor examining sequoia seedlings, convinced they'd be affected by the heat and the drought.

"They all looked really happy," he says. "I sat back, scratched my head and looked up, and there was a huge adult giant sequoia that had a lot of foliage die-back in it. That really got us interested, and we figured the drought was probably the cause of that. And that created a cascade of studies."

They found that a significant number of older trees that had shrugged off the Dust Bowl in the 1930s were losing as much as half of their leaves.

"Ten per cent of the trees had 25 to 50 per cent die-back," says Koren Nydick of the U.S. National Park Service. "This is the first time that this kind of foliage die-back has been observed since this has been a national park."

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If there's a positive from this tree-killing drought, it's this: for Das and his team, it's literally a dry run. A chance to improve their models in order to better predict what will happen in North America when this hotter, drier climate is the norm.

"This tree here is maybe a thousand, maybe two thousand years old," Das says, looking at the next giant sequoia he's about to climb.

"It's dealt with severe conditions, extreme droughts, fires in the past. They're really resilient trees, but every species, every organism, has a limit, and in the future, there may be a point where drought impact becomes so severe that they shed all their foliage, they stop growing. Maybe at some point, they get susceptible to insects or disease, and start to die back."