Posts Tagged: forest health
In response to California's growing tree mortality crisis, the Little Hoover Commission held a public hearing on California Forest Management yesterday (January 26) at the state capital in Sacramento.
Professor Scott Stephens, a fire scientist in the department of environmental science, policy, and management, delivered the opening remarks. He provided background on the causes and magnitude of tree losses happening across the state. "Our forests are not in a resilient condition," he said. "Past management actions, including fire suppression and logging focused on large trees have produced forests today that are much more vulnerable to fire and drought-related mortality." Stephens made suggestions for legislation, policy, and forest management techniques that could help restore resilience to California's forest ecosystems and prevent future mortality crises. He also offered ideas on how the state could better work with private landowners as well as the federal government to promote healthier forests.
Reposted from UC Berkeley News
Todd Dawson's field equipment always includes ropes and ascenders, which he and his team use to climb hundreds of feet into the canopies of the world's largest trees, California's redwoods.
It's laborious work, but he'll soon be getting a little help. From drones.
The need is urgent, Dawson said. Since 2010, more than 102 million trees, mostly pines and firs, have died in California because of drought, 62 million in 2016 alone. Why are pines and firs succumbing, but the thousand-year-old sequoias surviving, and will that continue into the future?
In August, he and Gregory Crutsinger, a plant ecologist and head of scientific programs at Parrot, performed the first test of a drone, a quadcopter, equipped with a state-of-the-art multispectral camera that takes photos in red, green and two infrared bands. Called the Sequoia, the camera works like more expensive satellite and airborne sensors, measuring the sunlight reflected by vegetation in order to assess physiological activity or plant health.
“Before, a team of five to seven people would climb and spend a week or more in one tree mapping it all around,” Dawson said. “With a drone, we could do that with a two-minute flight. We can map the leaf area by circling the tree, then do some camera work inside the canopy, and we have the whole tree in a day.”
After the data and photos were stitched together by a software program called Pix4D, Dawson and Crutsinger ended up with a three-dimensional representation of the foliage that his team had never seen before – information that will be used to determine how much carbon the tree takes up each day and how much water it uses, the basis for assessing what might happen with higher carbon dioxide levels in the atmosphere and less water on and in the ground.
“With repeat flights you can watch a forest grow without ever actually measuring any trees in the forest,” Dawson said. “I think drone technology holds a lot of promise to do some very innovative science over time and in three-dimensional space with a relatively cheap tool. It is really pretty amazing.”
Monitoring the health of the state's iconic sequoias is just one instance of how drones, combined with state-of-the-art sensors, can benefit science, Crutsinger said.
“Drone technology is getting much cheaper, but stitching and photogrammetry are innovating at the same time,” he said, referring to the science of making measurements from photos. “That is the backbone of the whole new commercial drone industry: not just the ability to capture the data, but also to process very high-resolution photos into millions of points that generate a three-dimensional model. This is going to help science but also environmental monitoring, agriculture and even construction sites.”
Crutsinger, a former Miller postdoctoral fellow at UC Berkeley, is asking other scientists to propose research collaborations with Parrot in exchange for free drones, cameras and analysis software. These Climate Innovation Grants are open to any student or researcher around the world.
Monitoring a changing environment
Dawson is now assessing how best to use the initial data and the drone and camera to answer questions in plant ecology. For the giant sequoias (Sequoiadendron giganteum), which he studies in the University of California's 320-acre Whitaker Forest just outside Sequoia-Kings Canyon National Park, he anticipates learning a lot more about their physiology than can be achieved by roping onto the canopy. Knowing the leaf area alone is a key advance, since he and his team have been able to model only the trees' branches and twigs, from which they estimate leaf surface.
“If we know how much area is there, I can tell you how many tons of carbon per meter squared per day was fixed by that forest, and how much water was used by that leaf area per day. You can start to get at rates of carbon exchanged between the tree and the atmosphere and then at rates of carbon sequestration,” he said. “These are important numbers for our forecasting models, so we can say, ‘If the climate goes up by 2 degrees, or it gets drier by 10 percent, what the hell is going to happen to that productivity?' All of a sudden you have power to really measure the pulse of the Earth, which is a really hard thing to do at large scales.”
Dawson is keen to see how drones and specialized sensors can aid his other research, which involves not only giant sequoias but also coastal redwoods, California's oaks and the canopy epiphytes in the clouds forest of Costa Rica. But he also sees a wealth of other possibilities.
“I think this is one of the tools for ‘change detection' that we are going to find is a game changer,” he said. “We can do this quickly and accurately over natural lands and agricultural lands and forest that burned and places that were hit by hurricanes or droughts, and look at the changes taking place and why they are taking place much more easily than we did before.”
Dawson doesn't plan to give up climbing trees, though. Some data will still need to be captured in the tree tops, if only to connect drone observations with tree physiology and ecology.
“The low-hanging fruit right now is really, what basic-level things that take up a lot of time can we replace with the drone, and what do we still need to do with boots on the ground in the field,” Crutsinger said. “If we can just save time and person power, that is most of the cost of doing scientific research, particularly in ecology. We are looking to augment what already happens on the ground — or in this case the crown — and then think about what new questions we can ask as well.”
Reposted from the UCANR News Blog
Even though there has been a deficit of fire in California forests for decades, their future is not hopeless, said UC Berkeley fire science professor and UC Agriculture and Natural Resources researcher Scott Stephens in an interview with Craig Miller on KQED Science.
"The next 25 to 30 years are paramount. If you begin to do restoration, reduce density, make forests more variable in pattern, and less fuel, when you have episodes of drought and fire, it's going to be fine. The forests have been doing this for millennia. It's going to be fine," Stephens said.
However, under current conditions, in which fires have been regularly suppressed, the situation is dire.
"The forests used to burn every 12 to 15 years, but most places haven't been touched for 50 to 100 years. Today we have areas with 300 or 400 trees per acre, where you used to have 50 to 80," he said.
Even though, Stephens said he is an optimist. "There's still opportunity today to do restoration, so that when it does get warmer and warmer, as projected, the forests will be able to deal with that, deal with insects and disease and keep themselves intact."
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. “
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.