X-ray technology reveals California’s forests are in for a radical transformation

Thomas CurwenContact Reporter LA Times, October 20, 2015

Full Article with Illustrations

Biologist Greg Asner first heard the numbers in April, but they did little to prepare him for what he saw.

The Forest Service had estimated that nearly 12.5 million trees in the state’s southern and central forests were dead. But as Asner peered down upon the same forests from his airplane at 6,000 feet, he saw something far worse.

California’s drought-parched landscape was poised for a radical transformation. Much of the low-elevation forests near Mt. Pinos in the Los Padres National Forest and in Pinnacles National Park were going to disappear if trends continued.

A scientist with the Carnegie Institution for Science, Asner has a practiced eye for forest health, and with instruments aboard his plane that give him X-ray eyes into the foliage, he is able to assess not just dead trees but trees so stressed by the drought that their death is likely.

For three weeks this summer, he and his team flew out of Sacramento and Bakersfield, recording the devastation. Even if the drought were to end in a historic El Niño this winter, Asner worries that the most stressed trees will continue to fail.

The U.S. Forest Service shot this video of the Stanislaus National Forest in the central Sierra Nevada in July. Flying at about 1,000 feet, covering about five acres per second, Forest Service observers count dead trees — conspicuous for the brown foliage — and extrapolate over plots that are the approximate size of a football field.

There is no saying which trees will die, but by his estimation the count statewide could be close to 120 million — as much as 20% of the state’s forests.

Tarnished beauty

On a hot summer morning, Asner boards his Dornier 228, a twin turboprop, at McClellan Airfield on what he hopes will be the final day of his survey. He needs to fly along the coast toward the Oregon border, but conditions are deteriorating.

An armada of firefighting aircraft has taken off at dawn to fight an outbreak of new wildfires to the north. The air is hazy with smoke.

Above the city of Santa Rosa, the plane veers northwest over the forests west of Guerneville toward the Lost Coast.

Asner, 47, sits in the cabin with Robin Martin, who manages the instruments and relays navigation instructions to the cockpit. They work in front of two monitors. She’s a lefty and he’s a righty, so they share a mouse pad. It helps that they are married.

To understand how Asner’s instruments work, you have to first step inside a leaf. There amid the busy factory of photosynthesis, water molecules are bending, stretching, rotating and vibrating.

Greg Asner’s vivid topographic images of Crescent Meadow in Kings Canyon-Sequoia National Park are created from data collected by an onboard spectrometer and laser. Healthy trees are blue, and drought-stressed trees run from mild (yellow) to severe (red).

These motions resonate into the atmosphere as reflected light, which is picked up by an on-board spectrometer that divides it into 480 bands from ultraviolet to shortwave.

Much like star light reveals a star’s distant chemistry, these bands are analyzed for their chemical content. Water is the primary focus: The more water in the leaves, the less reflected light, and the more reflected light, the drier the foliage.

The spectrometer works in conjunction with a laser that fans out beneath the aircraft, creating a 3-D image of the forest below.

By marrying the data from the spectrometer and the laser, Asner creates topographic images that show the condition of the forest. Healthy trees are blue, and drought-stressed trees run from mild (yellow) to severe (red).

The images help him to correlate terrain and tree stress. Higher tree stress, for example, often occurs on steep slopes and near meadows.

For Asner’s mostly Canadian crew, the Golden State is a tarnished beauty.

“It’s just burnt,” says pilot Don Koopmans of Saskatchewan.

Asner’s assessment is equally blunt.

The mountains ringing Los Angeles are “a tinderbox.”

The oak forests in the Sierra foothills are “in big trouble.”

Pinnacles is “not a happy place for a tree,” and the forests northwest of Redding are surprisingly compromised.

To explain what 120 million trees dying across the state might mean, Asner paints a picture of California’s ecological diversity and size. He then takes out his calculator.

He estimates there are 585 million to 1.6 billion trees in the state’s forests and apologizes for not being more precise. An accurate census, he says, has never been conducted, but 120 million represents 7% to 20%. Under normal circumstances, forests lose between 1% and 1.5% of their trees annually.

“At what point will the forest change into something else? We don’t know,” Asner says. “We don’t know when the lack of rain will lead to runaway conditions where the forests are beyond repair.”

Such a transition, especially in the lower elevations, is already underway in parts of the West, where nearly 6 billion trees — 13% of the area of western forests — died from 1997 to 2010 because of drought and the bark beetle.

Yet as grave as the effects of the drought have been, Asner insists there is hope.

“If I looked around and thought there was no way to deal with these problems, I would be pessimistic,” he says. “But there is a way with effective management.”

Among other things, aerial images can help land managers identify vulnerable terrain and consider how to strengthen stressed trees and protect healthy ones.

A march uphill

The study of forests is a formative science, and conclusions — like a definitive number for the trees that will die — are hard to come by.

Park Williams, a bioclimatologist at the Lamont-Doherty Earth Observatory at Columbia University who has been studying the California drought, is not surprised by Asner’s numbers.

If only half succumb, it would register as a very big event, Williams said.

“Think of it as one gigantic ax swing at the forest,” he said. “It takes a huge chunk out of the population, and if we see two or three more of these droughts, then that’s even more ax swings.”

Jeffrey Hicke, an associate professor in the department of geography at the University of Idaho, said that regardless of current tree mortality rates, the state will not lose its forests entirely. But he adds, based on the observations, the low-elevation forests are in greatest jeopardy.

Beyond this year’s drought, as climate change brings warming, tree species will migrate, Hicke said. Older trees will die, and younger trees will take root.