Given California's changing climate, should Sierra Nevada residents replant pine trees after so many died during the 2010-2016 drought? The short answer is yes, says Susie Kocher, UC Cooperative Extension forestry advisor.
“We have every reason to believe that pines will continue to be an important part of mixed conifer forests in the Sierras,” Kocher said.
Dead trees can be seen in the foreground and on the distant mountain side. (Click on photos for higher resolution.)
Kocher spoke at a meeting for UC Master Gardeners, volunteers who provide landscape advice to the public in California. Questions have been coming in to Master Gardener hotlines from mountain residents wondering what to do after unprecedented tree loses in the last few years.
Most California forests are suffering from severe overcrowding due to 100 years of aggressive fire suppression and selective harvesting of the largest and most resilient trees. They were then subjected to five years of drought.
“There were just too many stems in the ground,” Kocher said. “The drought was very warm, so trees needed more water, but got less. These were optimal conditions for bark beetles.”
Western pine beetle is a native pest that attacks larger ponderosa pine and Coulter pine trees weakened by disease, fire, injury or water stress. Bark beetles are tree species specific, so other beetles target other species of trees in California's mixed conifer forests. Typically, bark beetles bore through tree bark and create long winding tunnels in the phloem. An aggregating pheromone attracts additional bark beetles to the tree, and heavily attacked trees invariably die.
Healthy pine trees can fight off bark beetle attack by secreting pitch. Trees weakened by drought are unable to fend off an attack. In this photo, a pine beetle is stuck in pitch that oozed from the tree.
Evidence of bark beetle attack are exit holes on the outside, left, and winding galleries under the bark.
During the drought, 102 million Sierra Nevada trees died from bark beetle attack or simply lack of water; 68 million of those died in 2016 alone. But after the abundant rainfall in the 2016-17 season, the bark beetle population seems to have crashed.
Landowners with 20 acres or more may be eligible for a state cost-sharing program to remove trees, reduce the fire hazard and replant new seedlings. Landowners in mountain communities who wish to revitalize their properties can contact local UC Master Gardeners for recovery advice.
UC Master Gardeners are plant enthusiasts who have passed an intense training program presented by UC academics. They participate in continuing education annually to update and maintain their knowledge. More than 60 Master Gardeners from Mariposa, Madera and Fresno counties gathered in Oakhurst in October to learn from UC scientists how to work with mountain homeowners whose towering trees have died. Similar training sessions, all funded by a grant from UC Agriculture and Natural Resources, were held in El Dorado and Tuolumne counties in June.
UCCE specialist Jodi Axelson points out bark beetle damage.
“There is life after beetles,” said Jodi Axelson, UC Cooperative Extension forestry specialist at UC Berkeley.
“Eco systems are stretched, and then they come back,” she said. “You must remember the time scale of forest change is long and pines have been a major species in the Sierra Nevada for at least 28,000 years. As long as there have been pines, there have been bark beetles.”
The scientists suggest that people who own forestland take a step back and assess the landscape after their dead trees have been removed.
“We're seeing a lot of young cedar and white fir surviving the drought. Oaks seems to be doing really well,” Kocher said.
She suggests landowners thin young trees so available sun and soil moisture are focused on the healthiest trees. Water seedlings that are receiving more sun than before to reduce stress. Planting native conifers is the best option. Due to climate change, she recommends choosing trees from a slightly lower elevation to hedge against warmer temperatures in the future.
Pines are adapted to the California forest, but may need help to regenerate. When the ground is moist in the late fall or spring, plant seedlings 10 to 14 feet apart. New trees should be planted well away from homes to maintain defensible space and at least 10 feet from power lines.
“Please don't set them up for future torture,” Kocher said. “That's just sad.”
UCCE forestry advisor Susie Kocher, center, speaks during a field trip to a forest where many trees were killed by bark beetles.
To help the new trees become established, cover the ground around the tree, but not touching the bark, with two or three inches of mulch and irrigate weekly during the dry season for the first few years.
Questions about special circumstances may be directed to local UC Master Gardeners. Find the local program here: http://mg.ucanr.edu/FindUs/
Pouch fungus is evidence of a bark beetle kill. The beetles carry fungus into the cambial layer of the tree on their bodies. On recently killed trees, small white conks, the fungus' fruiting body, issues from bark beetle tunnels.
UC Master Gardeners learn from experts about replanting conifer forests.
UC Santa Cruz music professor David Dunn has joined forces with two forest scientists from Northern Arizona University to combat an insect infestation that is killing millions of trees throughout the West.
They are applying the results of nearly a decade of acoustic research in an unconventional collaborative effort to stop bark beetles from tunneling through the living tissue of weakened, drought-stressed pine trees.
The trio has now received a patent for a device that uses sound as a targeted sonic weapon to disrupt the feeding, communication, reproduction, and various other essential behaviors of the insects.
Dunn explained how this research came about.
“When massive tree death started occurring in Northern New Mexico where I was living, I became curious if there were sounds associated with such a large amount of biological activity,” said Dunn.
“At that time there was still the assumption that this was the result of a local bark beetle infestation due to drought conditions. Since then, we have come to realize that this was not just a local outbreak but one of many outbreaks across all of the western states and Canadian provinces that has been driven by climate change conditions. Many scientists think that we are experiencing the largest insect infestation of North America in the fossil record of the Earth,” he added.
Dunn spent a few weeks thinking about how to listen to the interior of trees and soon came up with a simple listening device that cost less than $10 to build. Designing unique and inexpensive devices in order to listen to sound had long been a part of his artistic work.
“After making hundreds of hours of recordings inside hundreds of trees, I made a large sound composition that represented the incredible diversity of sounds made by a couple of species of bark beetles and their changing responses to the life cycle of tree hosts that they invade,” said Dunn. “This was released as a CD (The Sound of Light in Trees) that garnered a lot of attention from both the sound, art, and music community, as well as various scientists involved in bio-acoustic research.”
“After that interest emerged, I was approached by my future colleagues at Northern Arizona University who not only wanted to replicate what I had done, but to collaborate on how to push this research further. These further results led to the device and protocol that we have just patented.”
Dunn noted that it is very unusual for a scientific patent to be awarded to an artist and added that there are very few examples of concrete results from collaborations between artists and scientists.
“My contribution to the project mostly concerned the technical design aspects of the audio, electronic circuit designs, and the novel sound gathering techniques,” Dunn explained. “In a very real sense, this represented a kind of reverse "tech transfer" from the arts to the sciences. Historically, it has usually been the other way around.”
“We have now entered into a period of common interests between art and science largely driven by the commonality of digital tools,” Dunn added.
“Artists are now just as involved in designing such tools as the scientific community and often create software and instrumentation in order to facilitate their creative visions that may ultimately be of even greater value to scientific research. I think that this was one of those instances and a couple of fortuitous events conspired to allow something interesting to happen.”
Dunn observed that one important aspect of art/science collaborations is the peculiar ability of artists to trust their imagination over their rational faculty.
“Most of the best scientists I know have fantastic and expansive imaginative capacities but often have to strategically mask those skills in order to operate within disciplinary and professional constraints,” said Dunn. “I personally believe that science must be a deeply rigorous enterprise, but it is not an either/or issue. It is the balance between the rational and imaginative that will ultimately solve the most serious problems that threaten us.”
“Artists can sometimes ask the pithy or embarrassing question that needs to be asked, or cuts across disciplinary constraints, or politics, without paying a professional price. As Gregory Bateson, a former faculty member of UC Santa Cruz put it: ‘rigor alone is paralytic death, imagination alone is insanity.'"
Dunn said that he and his colleagues at Northern Arizona University — Richard Hofstetter and Reagan McGuire — hope to produce a range of products as a result of their patent to combat bark beetles, as well as other insects related to them.
He added that scaling up the device to be effective in saving large forests might be possible through the use of local wireless or FM broadcast to protect select areas of forest, depending on how cheaply they can produce an effective system that can be applied to individual trees.
“One major obstacle is the issue of how to miniaturize the analog circuits and sample playback,” said Dunn. “One of my brilliant graduate students, David Kant in music, has been working on putting all of this into digital form and has largely succeeded. If we can solve that problem and come up with viable output transducers, amplification, and solar power solutions, it's very doable.”
This winter, a generous amount of rain and snow has fallen on California, but it can't erase the brown swaths of dead and dying trees in the Sierra Nevada caused by five years of drought and decades of forest mismanagement.
Fire suppression and the harvest of the largest and most resilient trees in the forest led to a large population of weak trees. The prolonged drought further weakened the trees' defenses against native insects. Aerial detection surveys show that more than 102 million trees have died since 2010; more than 62 million died in 2016 alone. Public and private landowners are now struggling to recover from this natural disaster.
UC Cooperative Extension forester and natural resources advisor Susie Kocher recommends dead trees be removed and the landscape reevaluated.
“The dead trees will eventually fall,” Kocher said. “Removing trees around homes and other buildings is especially important for safety. Also, when they fall on the ground they become large fuels on the forest floor, leading to more intense fires.”
Dead trees in the Sequoia National Forest. (Photo: U.S. Forest Service)
The cost of removing the trees can be substantial. The State of California is funneling disaster relief funds through California counties, utilities are felling trees that pose a threat to power lines, and local jurisdictions are removing trees that could fall on roads and other public infrastructure. However, most tree removal is the responsibility of private landowners.
When the dead trees are gone, before considering replanting, Kocher suggests Sierra residents carefully assess what has survived.
“There is often a lot of live vegetation remaining,” Kocher said. “Make a map and mark where you find living trees and shrubs and identify them by species and size. If you have a significant number of trees left, you may not need to replant.”
Kocher suggests nurturing the remaining young trees.
“You may want to thin trees out so that available sun and soil moisture are focused on the healthiest individuals. Some watering in the summer may help counter stress caused by increased solar radiation,” she said.
If removing the dead trees leaves the landscape too bare, replanting native conifers is a good strategy. Conifers include pine, cedar and fir trees, but in California's dense forests, firs and cedars – which do well in shady conditions – are beginning to dominate. Replanting may be a time to give native pines – such as Jeffrey, ponderosa and sugar pines – a chance to recover ground.
Replanting may be a time to give native pines a chance to regain a foothold in Sierra forests.
“The fact that many pines have died does not necessarily mean they are no longer adapted to your location, even with our warming climate,” Kocher said. “There may be a few locations that are less suitable for trees that have grown there in the past, but for most areas, local growing conditions should support native conifers in the near future.”
Native plants and shrubs that died during the drought or were damaged during tree removal will likely come back on their own without replanting. Shrubs and oaks can re-sprout and native herbaceous plants generally store seed in the soil that will grow under native rainfall conditions.
Replanting of trees also gives landowners the chance to shape the landscape for best effect. Kocher offers the following recommendations on replanting trees in natural landscapes:
Space trees at least 10 feet apart.
Trees and flammable vegetation should be kept at least 10 feet away from the home, planted sparsely within 30 feet of the home and spaced widely enough in the 30 to 100-food zone so the crowns of the trees will not touch when they are mature. Beyond 100 feet, trees can fill into a more natural looking forest.
Plant trees at least 10 feet from power lines.
Do not plant trees within the road right of way to prevent interference with snow clearance, maintenance and construction projects.
Plant pines where there is a lot of sun. Do not plant sugar pine on the driest sites.
Avoid planting where the mature trees will block desired views.
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.
Using climate data and aerial tree mortality surveys conducted by the U.S. Forest Service during four years (2012-2015) of extreme drought in California, they found that when a drought hits the region, trees growing in areas that are already dry are most susceptible.
The research also showed that the effects of drought on forests can take years to surface, suggesting that such effects may linger even after the drought has ended.
Southern Sierra Nevada trees are most vulnerable
The study said that trees in the driest and densest forests are the most at risk of dying in an extreme drought. In California, that makes crowded stands of trees in the Southern Sierra Nevada the most vulnerable in the state.
The concept is simple: Trees in dense forests are like multiple straws competing for the same glass of water. In wet climate conditions, that competition goes largely unnoticed. But when it's dry, few are able to quench their thirst, setting the stage for mass mortality.
‘How much drought a tree can take'
“Our analysis found out how much drought a tree can take,” said UC Davis Ph.D. student Derek Young, who co-led the study with Jens Stevens, a UC Davis postdoctoral researcher during the study who is currently at UC Berkeley, and Mason Earles, a postdoctoral researcher at Yale University. “If forest managers want to get the biggest bang for their buck in reducing forest vulnerability to drought, this study suggests they should focus on the densest stands in the driest areas. And when we reestablish forests burned by severe wildfire in these areas, we should plant at lower densities from the beginning.”
Tree mortality in the Sierra Nevada in 2015 was the worst in recorded history. The U.S. Forest Service aerial tree mortality surveys in 2015 estimated 29 million trees in California had died after four years of extreme drought.
Though the drought began in 2012, major effects on trees did not appear immediately. While some trees died every year, mortality spiked only in the fourth year of extreme drought.
Tree mortality a delayed reaction
In a blog post he wrote on the subject in May 2016, Young noted: “This observation highlights the fact that tree mortality can take several years to respond to drought. Such a delayed response is often observed in studies of drought stress, and the existence of this delayed response hints that we are likely to observe high mortality well into 2016 and potentially beyond, especially in Southern California.”
Indeed, surveys conducted by the U.S. Forest Service in 2016 estimated an additional 62 million trees died that year.
Other study co-authors include UC Davis associate professor Andrew Latimer, and Jeffrey Moore, Adam Ellis and Amy Jirka with the USDA Forest Service.
Study authors were supported by a National Science Foundation Graduate Research Fellowship, EPA STAR Fellowship, and a USDA Hatch Project.