Climate Change
Forestry

Suzette Sommer .. posting to Facebook about the health of trees in the forest

Burgess COMMENTARY

Peter Burgess

Suzette Sommer 11 hrs · FB says I can't post this because it is 'abusive.' I am going to cut & paste it.

'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.

USGS ecologist Nick Ampersee chops into a tree in order to find out what killed it.

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.'

Warming temperatures to blame

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.

'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.

Dying: Thirteen per cent of trees in the study areas in Sequoia National Park are dead.

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.

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.'

Canada's boreal forest, which stretches across the north of the country, is one of the world's largest intact forests. According to Tague, it may be particularly vulnerable as you move further north.

'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.'