Reprinted from California Magazine
The recent rains have blunted the psychological impact of California's four-year drought, washing down the streets, perking up the landscaping, and heightening anticipation for a stormy El Nino-driven winter. We know, however, that one wet year is highly unlikely to end water shortages. What we may not fully grasp is that the damage done to the state's forests is so far reaching that it may be permanent.
How bad is it? Really, really bad. Horrendous, in fact. Sally Thompson, an assistant professor in UC Berkeley's department of civil and environmental engineering, cites the status of the state's iconic giant sequoias as an example. Thompson notes that Cal biology professor Todd Dawson has been monitoring the biggest trees on earth, “and has found that they're extremely stressed. They're dropping leaves—some of them may die. These are trees that have lived 3,000 years, enduring a wide range of environmental conditions, including other droughts. And now they're being killed by this drought. That's suggestive of what we're facing. We're heading into uncharted territory.”
And it's not just giant sequoias. Virtually all of California's trees are drought-stressed, and many are going down for the count. Thompson observes the U.S. Forest Service conducted flights over 8.3 million acres of woodland in the southern Sierra, the Central Coast and Southern California in April and concluded that about 10 percent of the conifers and oaks—about 12.5 million trees—had died in recent months. They had either expired directly from drought or succumbed to bark beetles, which attack weakened trees.
The situation has only grown more grim. Two weeks ago, Gov. Jerry Brown declared a state of emergency, warning that the U.S. Forest Service estimates “more than 22 million trees are dead and that tens of millions more are likely to die by the end of this year.” He asked for federal assistance and called for an accelerated program to cut and clear dead trees, expand the practice of prescribed burns and temporarily allow more burning of wood waste.
Greg Asner, a biologist with the Carnegie Institute for Science, used spectrometers and lasers to evaluate forest canopies on flights out of Sacramento and Bakersfield. The procedures yielded 3-D topographic displays that show the forest in varying shades of blue (healthy) yellow (somewhat stressed) and red (deeply stressed to dying or dead). Bottom line: There's a lot of red in them thar hills. Asner concluded about 20 percent of California's forests are doomed—up to 120 million trees.
The images reveal the trees are dying in a mosaic pattern, says Thompson.
“You'll see patches of dying trees in the middle of healthier forest,” she says. “That's probably due to such things as south-facing slopes or shallow soils. You'd expect such areas to experience (drought-related) stress first. But there's a tremendous volume of dead wood building up all across the forests, and that's pointing to a future that is potentially very
Such a vast accumulation of fuels could lead to wildfires that are perhaps unprecedented in their ferocity. They could be so intense and of such a vast scale that they could lead to broad “ecotonal shift” —the evolution of entire forests from one vegetative regime to another. Ponderosa pine forests, for example, could convert to chaparral fields. Oak woodlands could change to grassy savannas. (As California previously noted, such ecotonal changes already may be occurring on Mt. Laguna in Southern California.)
That all sounds pretty apocalyptic no matter how you burn it, but Thompson observes we don't have to just sit back and take it. It turns out there's quite a bit that could be done to fireproof our forests—and perhaps increase water availability in the process. All it will take is a fair amount of money and political will.
“It's clear that there is more standing biomass—trees—in our forests than existed before active fire suppression began a century or so ago,” says Thompson. “Studies show that the canopies are heavier, and the forests are more vulnerable to fire as a result.”
A little background: Prior to Euro-American settlement, California's coniferous forests were characterized by extremely large, widely-spaced trees. Annals of the day—both textual and pictorial— made it clear that you could ride a horse through the forests unimpeded. There was little or no fuel (branches and dead trees) on the ground. The character of the forests was due to the occurrence of fire, both natural and human-induced; California's natives burned the forests periodically to make hunting easier and encourage the growth of food plants, including acorn-bearing oaks, seed-producing grasses, and bulbs.
The good news: The forests of our forebears probably can be reclaimed. All we have to do is burn and cut down a lot of trees.
In the old days, fire noodled around in a low-energy fashion on the forest floors, killing insect pests, nibbling back the underbrush, and converting deadwood to ashes that ultimately nourished the great pines and firs. Today, wildfires rip through entire landscapes of closely-packed trees, immolating everything down to mineral earth.
“Ultimately, the fires can be so intense that they take out all tree seed sources,” says Thompson, “so the system shifts to chaparral.”
Today's dense forests also have less biodiversity and suck up much more water than the forests of yesteryear. Thompson says studies of today's Sierra Nevada forests indicate they transpire 35 percent more water—that is, extract it from the ground through the roots and transfer it to the air as vapor via foliage—than 19th Century forests.
The good news: The biologically rich, fire resilient and amply watered forests of our forebears probably can be reclaimed. All we have to do is burn and cut down a lot of trees.
“There are three ways to go about it,” says Thompson. “Mechanical thinning, prescribed fire, and managed fire.”
Mechanical thinning would be the removal of trees by chainsaws or heavy equipment. Prescribed fire would be controlled burning—setting blazes when fuels are relatively damp and conditions are cool and humid, allowing for fires that reduce the forest canopy without destroying every standing tree and living creature. Managed fire is basically letting nature run its course. Wildfires would be allowed to burn in unpopulated areas, ideally when weather conditions aren't excessively hot and dry. The U.S. Forest Service is increasingly convinced of the wisdom of this approach. It recently inaugurated new management plans for three of California's national forests, approving managed fire for 50 percent of their acreages.
Thompson and UC Berkeley professor of environmental science, policy and management Scott Stephens are working on a project in Illilouette Creek basin in Yosemite National Park that seems to confirm the healing properties of fire.
“The National Park Service backed off fire suppression and began using managed fire in the basin in 1973,” says Thompson. “Scott and I are seeing strong evidence for increased plant diversity in the basin. There's much more meadowland and scrubland, and the resulting patchiness across the landscape reduces the risk for catastrophic wildfire. We're also seeing greater diversity in water conditions. There are more areas with persistently wetter soils than were recorded under the old completely forested state. We're now trying to determine whether these changes are increasing run-off from Illilouette Creek into the Merced River. “