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.

Buds on a Douglas fir. The buds become either new needles or cones. Photo: R.A. Howard from the USDA-NRCS PLANTS Database

Bud burst, when the buds on a tree begin to open up, marks the end of winter dormancy and the beginning of a tree’s growing season. Timing’s important: If a tree buds too early, it may be susceptible to a late frost. Too late, and it misses out on some or all of its growing season. As the climate warms, this delicate timing can go awry.

Scientists at the US Forest Service’s Pacific Northwest Research Station in Portland, Oregon, have developed a model to predict bud burst. They used Douglas firs in their experiments but also surveyed research on about 100 other species, so they expect to be able to adjust the model for other plants and trees.

Both cold and warm temperatures affect the timing, and different combinations yield different outcomes — not always intuitive. With plenty of hours of cold temperatures, trees need fewer warm hours to burst. So earlier spring warmth will drive bud burst earlier. If a tree isn’t exposed to enough cold, though, it needs more warmth to burst. So under the most dramatic climate change scenarios, warmer winters could actually mean a later bud burst.

Genes play a roll, too. The researchers experimented with Douglas firs from across Oregon, Washington, and California. Trees from colder or drier environments showed earlier burst. Trees descended from those lines could fare better in places where their warmer-and-wetter-adapted cousins live now.

The team, led by research forester Connie Harrington, hopes to use the model to predict how trees will respond under various climate projections. With that information, land managers can decide where and what to plant, and, if necessary, plan assisted migration strategies.

The study concluded that the near doubling in the mortality rate over several decades transcends forest types, elevation, tree size and species. The study will by published in Science this week.

Phil van Mantgem, who co-led the research team at USGS, said the spike in dying trees could lead to habitat destruction for forest wildlife. And while living trees absorb greenhouse gases, dying trees actually release carbon dioxide into the atmosphere, furthering the effects of global warming.

Usually, van Mantgem said, a small number of trees in a forest die each year and are replaced by new growth. However he’s observed that trees are dying so quickly that new growth is having trouble keeping up. He said one of the causes could be the West’s rising average temperature. While it rose only 1 degree (F) during the past few decades, he said it’s been enough to reduce the snowpack and melt the snow earlier, causing longer periods of dry weather and distressing forests.

Warm weather might also nurture insects and diseases that attack trees. Some reports have already tied destructive bark-beetle outbreaks to higher temperatures.

Nate Stephenson, another research team co-leader with the USGS, said the deaths, over time, could reduce the age of the western forests. “Tree death rates are like interest on a bank account – the effects compound over time,” Stephenson said. Stephenson worries that the increasing rate could lead to a bigger and more abrupt change in forests, similar to sudden and extensive die-backs observed in the southwest, Colorado and British Columbia.

Scientists from the U.S. Forest Service, and six universities collaborated on the study. Van Mantgem appeared on KQED’s Forum program today, along with host Dave Iverson, Climate Watch Sr. Editor Craig Miller and Inez Fung, author of a new study on seasons shifting from rising temperatures. Van Mantgem then popped up on NPR’s Science Friday. New York Times correspondent Andrew Revkin, author of the widely followed Dot Earth blog, also appeared and responded to recent polling on attitudes toward climate change.