KQED QUEST

Scientists are looking at climatic water deficit, the water plants need but don't have.

We hear a lot about how climate change will affect rainfall in California, but climate scientists are increasingly looking at a new indicator: water deficit.

“Climatic water deficit” relates to how much water plants need to survive. “It’s the difference between what a plant would use if it had the water and what is actually available,” Alan Flint, research hydrologist with the US Geological Survey, explained on Wednesday at the North America Congress for Conservation Biology.

The value combines temperature, rainfall, the soil’s capacity to hold water and how plants use water. In agriculture, farmers irrigate their crops to make up the water deficit, but plants in the natural world aren’t so lucky.

Using modeling, Flint and his colleagues are finding that the Bay Area’s water deficit is likely to increase, even under a wetter climate future. “We see that excess water go to runoff in the wintertime. But if you’re a plant species trying to live in March and April and growing leaves, you only have the water that’s in the ground,” Flint said.

Warmer air temperature increases evapotranspiration – the water lost through evaporation from soil and from plants themselves. That increases a plant’s demand for water.

“Water deficit is going to be a big issue. It’s what will control the health of forests in the Sierra Nevada. It will control landscape changes in the Bay Area,” said Flint.

That could include oaks, which are often found on north-facing slopes in the Bay Area, “where the water deficit is low. On the south slopes, we don’t see them there,” said Flint. In a warmer future, “if those areas where oaks live have the same water deficits as the south facing slopes, the oaks may not be able to regenerate there. They may survive, but they may not be able to regenerate.”

Water deficits could also have a large impact in the Sierra Nevada, which Flint calls a potential “worst case.” Water deficits are associated with fires and with forest die-offs. “It will really stress the plants and allow bark beetles or other things to come in and kill them. And it doesn’t have to change by a lot,” said Flint.

Susan Frankel/USDA-Forest Service

A patch of tanoak, killed by Sudden Oak Death, in the Los Padres National Forest in Monterey County.

Climate change is likely to wreak havoc on California’s forests. Extreme weather, wildfires and insect outbreaks will all take a toll. Add to those another looming threat: disease. Forest diseases like Sudden Oak Death, which has infected trees in 14 counties in the state, stand to benefit from the effects of climate change, to the detriment, obviously, of the trees.

Trees are big and long-lived. Tree pathogens, mostly fungi and bacteria, are the opposite. They’re mobile, able to blow around on the wind. And they reproduce and evolve rapidly. That’s the crux of the problem, according to Susan Frankel, a plant pathologist with the Forest Service.

“When you look at forest health and the balance between forest trees and the pathogens that attack them, it does seem, given climate change, pathogens get the better end of the deal,” she told me.

Frankel is working with a group of ecologists, funded by the Forest Service’s Western Wildland Environmental Threat Assessment Center, to better understand how climate change will affect tree diseases. In a recent report, they outlined possible impacts:

• Range and distribution of tree diseases will change.
• Warmer winter temperatures won’t kill pathogens that have historically been limited by cold weather.
• Prediction of disease outbreaks will me more difficult.
• The rate of evolution of tree diseases may increase.
• Other stressors caused by climate change — for instance, drought — will make trees more susceptible to disease.
• Climate change may open the door to invasions by non-native forest diseases.

Frankel is especially interested in Sudden Oak Death, which has killed more than a million trees in California. It needs moisture to spread and reproduce, and it thrives in warmer temperatures. “The pathogen blows in wind-blown rain,” Frankel explained. “It loves the weather we’re having right now.”

The study from the Forest Service weighs two possible future climate scenarios: warmer and wetter or warmer and drier. It finds, for the warmer and wetter option, increased damage from Sudden Oak Death is “High (very certain).” The warmer and drier option is “Low (moderately certain).”

The other diseases Frankel and her colleagues examined were Dothistroma Needle Blight, Swiss Needle Cast, White Pine Blister Rust, Cytospora Canker of Alder, Dwarf mistletoes, Armillaria Root Disease and Yellow-Cedar Decline.

sierrian/Flickr

Aspens live at high elevations in the Western United States, including in California's White Mountains and Sierra Nevada.

Throughout the West, aspens are quaking for good reason.

About 17% of the aspen in the Colorado Rockies have died in the last decade. That’s about one in every six trees. The widespread die-off, called sudden aspen decline, began after a severe drought and heat wave. So people studying the trees knew that’s what triggered the deaths, but they didn’t know what exactly killed the trees.

William Anderegg, a grad student at Stanford, with help from a team of scientists there and at the University of Utah, has zeroed in on the culprit, and describes the work in a paper published this week. There were two working theories: failures in photosynthesis, which would mean less food for the tree; or damage to the roots, which would mean less water. Anderegg found it was the roots.

“Our study provides a snapshot of what future droughts could hold for the emblematic tree of the American West,” Anderegg said in a press release. “Our results indicate an impaired ability to transport water due to drought damage plays an important role in the recent die-off of aspens,” .

With this research, scientists will be able to better understand and predict how forests will respond to rising temperatures and drier conditions.

More than 100 organizations, including the Natural Resources Defense Council and Defenders of Wildlife, signed on to a letter sent to Secretary of Agriculture Tom Vilsack on Monday, arguing that the proposal “fails to provide critical, concrete protections for the most precious resources of our forests — water and wildlife,” and that it “weakens the strong standards for safeguarding water quality and wildlife viability first issued in 1982 by the Reagan Administration and currently still in place.”

In a February press release announcing the new proposed rules, the USDA (which manages the Forest Service) touted the new proposal as creating increased protections for water resources and an “improved ability to respond to climate change and other stressors through provisions to restore and maintain healthy and resilient ecosystems.”

Last week a New York Times editorial explained the apparent discrepancy this way:

The Obama administration’s proposed rules… are full of high-minded promises about maintaining “viable” animal populations. But they are disappointingly vague on the question of how — and how often — the biological diversity of any particular forest is to be measured and what actions are to be taken to ensure its survival.

The net result is to give too much discretion to individual forest managers and not nearly enough say to scientists. This is dangerous because, over the years, forest managers have been easily influenced by timber companies and local politicians whose main interest is to increase the timber harvest.

Neil Lawrence, the director for the NRDC’s forest project, says one of the most vital pieces missing from the proposed rules is strong guidance for forest managers.

“These rules contain a lot of fine phrases, but where the rubber meets the road, they really don’t do the job,” said Lawrence. “They open up far too many opportunities for misuse of discretion, or simply bad mistakes made in haste, or ignorance, or lack of resources at the local level.”

California has 18 national forests which together encompass about 20 million acres.  The letter to Vilsack points out that most of the state’s snowpack lies within national forests, providing about 50 percent of the state’s drinking water. It also highlights the value of California’s national forests in terms of tourism dollars, endangered species habitat, and carbon sequestration.

The environmental organizations worry that without strong guidance from above, managers at the local level may not value these benefits as highly as they should.

From the Times editorial:

The rules, mandated by 1976 National Forest Management Act, are supposed to guide forest managers as they decide which parts can be logged and which should be fully protected. The act’s bedrock principle is that the health of the forests and their wildlife is to be valued at least as much as the interests of the timber companies.

“I think some at the Forest Service are really pushing hard to get more discretion to do as they see fit, and I think many of these are well-intentioned people,” said Lawrence.  “But they forget the many problems we have in national forests – the damage to the forests, to streams and wildlife, to recreational value, to scenic beauty – most of that damage has been due to the well-intentioned exercise of discretion. They’re forgetting how easy it is to get in trouble when you manage these lands.”

The public comment period on the rules is open until May 16th.

California's forests provide water, habitat for animals, lumber and tourism dollars, and they sequester carbon. (Photo: Molly Samuel)

For decades the federal government has touted the nearly 200 million acres of national forests and grasslands under its control as a “land of many uses.” But one “use” that’s seldom discussed is as a huge repository for carbon.

But clearly it’s on the minds of officials and scientists as the Forest Service seeks comments on its proposed new planning rule. National Forests and Grasslands are managed individually, but the planning rule guides how those management plans are developed. This new one is replacing a Planning Rule from 1982.

According to the Forest Service press release, some of the highlights in this new Planning Rule include

• Improved ability to respond to climate change and other stressors through provisions to restore and maintain healthy and resilient ecosystems
• Increased protections for water resources and watersheds
• More effective and proactive requirements to provide for diverse native plant and animal species

The Forest Service manages just under half of the forest land in California. Below is a handy map from their website (If you want to see all the federal land in California — not just National Forest — nationalatlas.gov offers this PDF map).

In celebration of the UN’s “International Year of Forests,” I recently went down the rabbit hole of trying to understand how much carbon California’s forests hold. Figuring that out is, according to Forest Service research forester Jeremy Fried, “An accounting problem. And like any accounting problem, you need to have accurate data.”

That’s been a challenge. Fried works on the Forest Inventory and Analysis Program (FIA), which is the Forest Service’s annual census of the nation’s trees. Unlike the census of the nation’s people, the goal isn’t to count every individual, but to count and measure plots of trees all over the country. But the sizes and locations of those plots have changed over the years, and that makes for unreliable data.

In fact, last year was the first time that Fried and other researchers were able to go back and re-measure the same plots. What he found was that on the 15 million acres of forested lands that the Forest Service manage in California, trees sequester somewhere on the order of 1.8 teragrams of carbon a year (almost two million metric tons).

Going forward, Fried says, as long as the funding holds up, the FIA will continue measuring the same plots, and not just in National Forests, but plots in all kinds of public and private forests.

One last note. Fried explained that carbon generally makes up half of the biomass of a tree. To calculate the biomass of a tree, researchers measure its width and height. But a tree isn’t a box, so you have to add in the branches, maybe you measure the stump separately, and what about the bark versus the stem? The list goes on. Just to give me a sense of how complicated this is, he gave me this number: 102,905. That’s how many ways there are of calculating the carbon content of a Douglas Fir. 102,905.

(Photo: Reed Galin/Lone Tree Productions)

In the last decade, tiny forest-dwelling beetles have wiped out pine trees on millions of acres in the Canadian and American West, including Southern California. The rest of the state has been largely spared, but forest ecologists say that’s likely to change.

Reporter Ilsa Setziol recently spent some time tracking these bugs with an entomologist from the US Forest Service. They found beetles at work in Jeffrey pines and coulter pines in the San Bernardino National Forest, east of Los Angeles.

You can hear her radio feature on The California Report, produced by KQED Public Media. She also put together a slide show, so you see for yourself how these tiny creatures — normally part of a healthy forest ecosystem — can, under the right conditions, quickly run amok.