- Author: Glen Martin
Reprinted from California Magazine
With perhaps one of the most intense El Niño ever recorded simmering like a massive coddled egg off the coast, Californians are bracing for precipitation on an epic scale. More than that: They're hoping for it. There is a general sense that even the rampaging floods that can result from a full-blown El Niño-driven winter would be tolerable as long as our reservoirs fill and aquifers recharge and we can get back to long showers and adequately watered hydrangeas.
This is a good place to insert a couple of caveats. First, choose your wishes carefully. Recall, if you were in California at the time, the great El Niño of 1997-98, and the vivid images it provided of nature running amok: Highway 70 disappearing into the vast, churning inland sea that was once the Yuba River, with dead cows, outbuildings and giant hissing propane tanks bobbing downstream. That was the year the dikes failed on the Feather River, and thousands of Yuba City residents fled the rising waters. After it was all over, one staffer with the U.S. Army Corps of Engineers chatted off the record, and said there had been very real fears that Folsom reservoir could have overtopped its dam. If that had happened, much of Sacramento would have flooded. People would have died. Four years of drought may have made people forget that California can be blighted by too much water as well as too little.
Second, observes Doug Parker, the director of UC's California Institute for Water Resources, the rain and snow may fizzle. A robust El Niño is no guarantee of record rainfall and snowpack.
“In fact, the research indicates a wet year for Southern California, but there's less confidence about a lot of precipitation for the north state, particularly in terms of snow,” says Parker.
And we need snow more than we need rain. Parker notes that intense rainfall can produce too much water too fast at the lower elevations and melt snow at the higher elevations. In such cases, the state's dams and reservoirs have to function as flood control structures; much or most of the water is shunted rapidly to the sea, not stored.
One wet winter could put a lot of water in our reservoirs and maybe help replenish some aquifers, but it will do nothing to address demand.
Further, cautions Parker, even an optimal El Niño that dumps heaps of snow in the Sierra without swamping the lowlands with Pineapple Express deluges may not get us back to “normal.” That's because surface water is only part of the issue. Brimming reservoirs alone cannot slake the state's thirst. According to theCalifornia Department of Water Resources, groundwater constitutes between 30 to 46 percent of the state's total water supply. Despite recent legislation to monitor and control groundwater withdrawals, pumping remains largely unregulated, and many of the state's aquifers are in “overdraft,” with more water being sucked up and out than trickling back underground. The results of this excessive pumping are particularly evident in the San Joaquin Valley, where massive ground subsidence—a sudden sinking or gradual sinking of the Earth's surface— is occurring as groundwater is withdrawn.
These effects are not temporary. Ground subsidence can destroy aquifer structure, reducing long-term storage capacity. And while heavy rains and deep snowpack are essential for recharging aquifers, the process isn't necessarily a rapid one.
“There are some areas where recharge happens fairly quickly, particularly if combined with decreased pumping,” Parker says. “But other areas may require decades or centuries to replenish. Also, you have to consider what you mean when you say ‘recharge.' In the Tulare Basin, the water table has fallen by hundreds of feet, it keeps dropping, and the pumping continues. So what does ‘recharge' mean? Getting water back up to 300 feet from 400 feet? What's your baseline? When water is that deep, it's unlikely you could get any significant or long-term replenishment from one year, especially considering the ongoing demand.”
And that may well be the ultimate rub: Demand. The problem with a state that has so many people and so much intensive agriculture is that water demand is by no means static. It's constantly moving, but it only moves one way: upward. No matter how much water we get, there will always be someone clamoring for it. Water rights claims exceed the amount of the state's developed water—the water controlled and distributed by government agencies—by 5.5 times. Even during the last four years of devastating drought, thousands of acres of new almond orchards have been planted in the Sacramento and San Joaquin Valleys, and almonds are a water-intensive crop, each tree requiring heavy irrigation for its entire productive span.
“One wet winter could put a lot of water in our reservoirs and maybe help replenish some aquifers, but it will do nothing to address demand,” says Parker, “so ‘getting back to normal' doesn't really speak to the biggest issues. People will always have a use for any water that's available. If we want a truly sustainable water policy, we can't be reactionary. We can't look at this from the perspective of one year, or a few years. We have to take a long-term view.”
- Author: Glen Martin
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. “
- Author: Faith Kearns
Reposted from the Confluence, Blog of the California Institute for Water Resources
When we think water in California, we tend to think big: the Sacramento River, the American, the Delta. But, the state is also filled with small headwater streams that can be particularly easy to overlook when, during the state's dry summers, they start to resemble a series of pools rather than flowing creeks. Adding insult to injury is a longstanding view that the fish and insect communities in these intermittent streams will be less diverse than those found in the larger rivers they run into.
It is against this backdrop that scientists at the University of California, Berkeley, with support from the California Institute for Water Resources, set out to study some small creeks in the northern part of the state. They have been both surprised and excited by the diversity they are encountering. For example, at John West Fork in Marin County, they observed California giant salamanders, California newts, and Pacific chorus frogs, along with imperiled steelhead trout and coho salmon. In nearby Pine Gulch, they have observed a similar suite (minus the coho salmon), including several pools supporting older steelhead trout. The presence of these larger animals is an encouraging sign of resilience. They also found an abundant and diverse range of small invertebrates like mayflies, stoneflies, caddisflies—insects that are an important part of the food chain.
“These are small streams that lack flow for part or most of the year, yet they are totally filled with life. Understanding how these tiny little aquatic organisms manage to navigate this crazy and variable landscape, and thrive in conditions that most species would find very challenging, is really cool,” says project researcher Michael Bogan.
This finding is a great reward for difficult field work in a setting where streams can go from several months of dryness to raging flood waters with a single storm. “There's a lot of slogging up and down stream channels, crawling over downed trees & logs, sliding on wet rocks, and avoiding poison oak and stinging nettle,” says Bogan, though you mostly get the sense that he doesn't mind.
“In the long run, it's really exciting to think about how we can use this understanding of species ecology to inform water resource management and maximize our ability to support aquatic biodiversity and mindful agriculture and water use. In many situations, I do believe we can have the best of both worlds,” says Bogan.
The full study results are in: Bogan, Michael T., Jason L. Hwan, and Stephanie M. Carlson. In Press. High aquatic biodiversity in an intermittent coastal headwater stream at Golden Gate National Recreation Area, California. Northwest Science. Contact email@example.com for a pre-press copy.
This research was supported in part through a grant to Principal Investigator Stephanie Carlson at the University of California, Berkeley from the California Institute for Water Resources in the University of California's Division of Agriculture and Natural Resources.
- Author: Susie Kocher
The fourth winter in a row of disappointing precipitation has triggered a die off of trees in the Sierra Nevada, most of which is now in ‘exceptional drought' status. The US Forest Service conducted aerial monitoring surveys by airplane in April 2015 and observed a large increase in tree mortality in the Southern Sierra (from Sonora south). Surveyors flew over 4.1 million acres of public and private forest land and found that about 20 percent had tree mortality on it, totaling over 10 million dead trees.
The Forest Service found severe mortality in many pine species especially ponderosa pine. On private lands along the foothills of the Sierras, surveyors found extensive areas of dead pines. Large areas of blue and live oak mortality were also suspected though it was too early in the season to be sure.
On the Stanislaus National Forest, areas with dead trees doubled since last year. Pine mortality, mostly caused by western pine beetle, was common at lower elevations. Over 5 million trees were killed on the Sierra and Sequoia National Forests up from the 300,000 trees killed last year in the same area. Conifer mortality was scattered at higher elevation, though surveyors note that the survey was conducted too early in the year to detect the full extent of mortality levels.
The insects killing trees in the Sierra are all native insects that are multiplying because of drought conditions. Native insects are a necessary part of the forest ecosystem that speed decay of wood back into nutrients, prey on other insects, and provide food for wildlife. They are normally present at low levels and cause tree mortality only in localized areas.
However, drought weakens trees and reduces their ability to withstand insect attacks. Normally trees use pitch to expel beetles that attempt to burrow into the tree through the bark. Weakened trees cannot produce the pitch needed to repel these beetles which are able to enter under the bark and lay eggs. Larvae feed on a tree's inner bark cutting off the tree's ability to transport nutrients and eventually kill it. Attacking beetles release chemicals called pheromones that attract other beetles until a mass attack overcomes the tree. Many beetles also carry fungi that weaken the tree's defenses.
Western pine beetle is one of the main culprits killing pines in the Sierra during this drought. It is a bark beetle, one of a genus of beetles named Dendroctonus which literally means ‘tree-killer'. Adult beetles are dark brown and about a quarter-inch long. Adults bore into ponderosa pines, lay eggs which develop into larvae in the inner bark then complete development in the outer bark. When beetle populations are high, such as during drought periods, even healthy trees may not be able to produce enough pitch to ward off hundreds of beetle attacks.
Western pine beetle often attacks in conjunction with other insects. Other beetles causing tree mortality in Sierra forests include mountain pine beetle, red turpentine beetle, Jeffrey pine beetle, engraver beetles (Ips) and fir engravers. Forests with a higher diversity of tree species are typically less affected because beetles often have a preference for specific tree species. Some species may attack only one tree type. For example Jeffrey pine beetles attack only Jeffrey pine.
Signs that bark beetles are affecting a tree include pitch tubes (streams or tubes of pitch visible on the trunk), small holes through the bark, or boring dust. If the tree is extremely water-stressed and cannot produce pitch, boring dust may be the only visible sign. Trees with needles that have turned from green to red are dead. Most beetles have emerged by the time trees turn red.
The best defense against bark beetles is to keep trees healthy so they are able fight off insects themselves. Widely spaced trees are typically less susceptible to successful attack by bark beetles since they face less competition for moisture, light, and nutrients compared to densely growing and overcrowded trees. Forest health can be promoted by thinning to reduce overcrowding (so each tree has access to more resources) and removing high risk trees during thinning (such as those that are suppressed or unhealthy).
For landscape trees of high value close to a home, watering may be one option to increase tree vigor against bark beetle attacks. Apply about 10 gallons of water for each inch of tree diameter (measured at chest height) around the dripline of the tree once or several times a month during dry weather.
There are some insecticides registered for bark beetle control, but all are preventative only. Carbaryl may prevent attack for up to two years, while pyrethroids can deter attack for up to a year. Spraying can be tricky because the chemical must be applied up to 50 feet up the trunk of the tree usually while standing on the ground. Since misapplication may have toxic consequences, any insecticide must be administered by a licensed pesticide applicator. All applications must follow the label. Though some systemic treatments applied to the soil or inserted into the tree may work in some cases, there is not a lot of documented evidence that they are effective against western pine beetle. No insecticide can prevent tree death once a tree has been successfully attacked.
- Author: Bill Tietje
Bill Tietje is a UC Cooperative Extension area natural resources specialist in the Department of Environmental Science, Policy and Management at UC Berkeley. He is based in San Luis Obispo.
UC Cooperative Extension's Master Gardeners have received many calls during the past few months concerning the poor condition of many California native oak trees, in both urban and rural landscapes. Many evergreen oaks, including coast live oaks, have brown leaves and thin foliage. Adding to the unattractiveness, a deciduous oak, the blue oak, dropped its leaves ahead of schedule. Although a tree may look unhealthy, it can recover.
Early leaf drop is a deciduous tree's adaptation for conserving water that it otherwise would lose through transpiration from its leaves, which can occur as long as the leaves are green.
More recently, another deciduous oak, the valley oak, kept its brown, dead leaves longer than usual. This could be due to the virtual lack of rainfall and wind last fall and early winter, both of which typically contribute to an earlier leaf drop.
So why are these things happening?
As you know, it's dry out there! In fact, the past 12 months have been the driest on record, going back to 1870. Not surprisingly, many oaks are under water stress—and they show it.
This situation reminds one of the conditions during the drought of 1988-1990, one of the most widespread and severe droughts in the state's history. Coincidentally during that time in three counties on the Central Coast, UC Cooperative Extension was conducting a study that included the monitoring of coast live oak, blue oak, and valley oak trees on study plots scattered throughout Monterey, San Luis Obispo and Santa Barbara counties. Many of the oaks looked stressed. Some of the trees succumbed to the drought. Small oak trees in the undergrowth and on steep terrain with southern exposure, and shallow, infertile soil, were most vulnerable. Such sites are typically drier than other slopes and orientations. However, large, mature trees—or, large branches on these trees—on more gentle slopes, also died. Usually there is not only a single factor that causes the decline and mortality of oak trees. Drought stress lowers the trees' defense, making the trees more susceptible to mortality factors such as decay fungi and boring beetles. Most likely the drought caused early death of some oak trees that would have persisted otherwise.
What can be done?
Surely our native oaks have been through droughts before. So the oak trees, other than the very small or very old trees, should be okay. Nonetheless, given the very low rainfall this year it may be prudent to give a valued tree in the urban landscape a “deep watering”.
A deep watering can be accomplished by moving a hose around under the tree's canopy during the day for a day or two at a low flow or a trickle stream, such that the water percolates into the soil, not simply run down the hill. Water a few feet away from the base of the tree to avoid inviting damage from crown rot caused by the fungi Phytophthora cinnamomi. Water-saturated soil increases the chances of infection of the tree trunk.
A deep watering followed by soil drying for a month or two should not harm the tree. In fact, a deep watering may be the best recommendation for invigorating your thirsty oak tree, thus providing some insurance that the tree will survive this current drought.
I should mention that unless California receives normal or better rainfall the rest of the rainfall season, it is likely that early leaf drop will occur next summer. Remember, as suggested above, the early browning and fall of leaves does not mean that your tree will die. This is simply the tree's way of adapting to conserve water when soil moisture is low. Unless the tree is severely weakened by some other cause, it will leaf out normally the following spring.
For more information: Tietje, W., W. Weitkamp, W. Jensen, and S. Garcia. 1993. Drought takes toll on Central Coast's native oaks. California Agriculture 47(6):4-6.