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.
Scratch that. The collections manager at the Essig Museum of Entomology, Oboyski worries about insects eating his insects—specifically, a family of beetles known as dermestids, which, should they make their way in, could reduce the museum's 6-million-plus specimens to powdery ruin. As any self-respecting entomologist will tell you, true bugs are only a subset of the much larger taxonomic class of Insecta. Indeed, Oboyski's ilk tend to be a bit pedantic on that point. “Bugs” is a colloquialism they'd squash if they could.
The dermestidae, often called skin beetles, eat skin, just as the name suggests. They also eat hair, hide, fur, feathers, and meat—basically, everything but bone. And while museum curators dread the damage the ubiquitous arthropods and their larvae can do, they also make use of them.
Oboyski points at one wall of the bunker-like space that houses the Essig. On the other side of the wall is Berkeley's Museum of Vertebrate Zoology. “The vertebrate people keep a colony of dermestids just on the other side of that wall there, to clean carcasses. They like them because they do such a thorough job of it, removing every last speck of flesh.” He says it's the same colony they've had since the museum started in the early 1900s. “They use a variety that's a little too large to get into my cases, fortunately, which is the only reason I can sleep at night.”
The tightly constructed, glass-topped wooden cases in which insects are mounted on pins are the entomologist's stock in trade. The Essig holds thousands of them, all slotted in racks on track shelving that can be moved by hand cranks. It's a vast bug library filled with row after row of meticulously preserved specimens, all organized by order, family, genus, species, and subspecies. Everything in the collection is of the phylum Arthropoda—many in class Insecta,but no few Arachnida.
Something you generally won't find in the Essig is any living insects, although on this particular day Oboyski was making an exception, hatching some Australian walking sticks in a terrarium. Most of the time, live bugs are verboten, and Pete has lights and pheromone traps set up to catch any of the little buggers that might sneak in.
“If you had told me 50 years ago that we were going to sequence DNA from these specimens, I would have said, ‘What are you talking about?' Now we do it all the time. … So that's my attitude in terms of preserving these … because I have no idea what they're going to be used for in the future.”
One of the largest university collections in North America, the Essig's regional emphasis is primarily on California, but it also expands to the Pacific Rim, including the islands of the central Pacific. Oboyski, a moth specialist who earned his Berkeley Ph.D. in 2011, has identified nine new species himself—seven from Hawaii, and two from Tahiti. The museum's namesake, Professor E.O. Essig (1884–1964), author of the seminal text Insects of Western North America, was chiefly an aphid man. (Aphids, incidentally, are true bugs, part of the order Hermiptera, which, like all the other true bugs, have mouthparts adapted for sucking juices from plants … or, in the case of bed bugs, blood from people.) Essig was one of the leaders of the California Insect Survey, which grew the collection considerably in the 1930s.
“Museum” is a bit of a misnomer in this case. The Essig is strictly a research collection, made available to scientists for all manner of legitimate study, but only open to the general public a few times a year: on Cal Day, Darwin Day, and, this year, Homecoming. That said, education and outreach are a part of the Essig's charter. Schoolchildren often visit on tours, and when they do, Oboyski will show off what he calls the “Oh, my!” collection. These are the stars of the insect world: the glorious blue morpho butterflies, bizarre walking sticks, and the giant rhinoceros and Atlas beetles, which look like they could topple walls. Indeed, pound for pound, these macrobeetles are among the strongest animals in the world.
But the oohs and aahs and occasional shrieks elicited by these specimens are only a small part of the collection's value. More important is the research role they play, perhaps especially in terms of documenting ecological change over time. To the disinterested, the Essig may seem like a mausoleum, better digitized and discarded. (And in fact, digitization is underway, in part through volunteer and crowdsourcing efforts, with about 10 percent completed so far.) But to Oboyski, the physical collection itself is a vast storehouse of information that is constantly being mined in new ways.
Think about it, he says; we now have CT scans that allow us to scan the internal anatomy. We can look at stable isotopes to study their diets and how they've interacted with the environment. We can grind them up and extract DNA.
“If you had told me 50 years ago that we were going to sequence DNA from these specimens, I would have said, ‘What are you talking about?' Now we do it all the time. Fifty years from now, I have no idea what people are going to be doing. … So that's my attitude in terms of preserving these. I want to preserve them as pristinely as possible for as long as possible, because I have no idea what they're going to be used for in the future.”
In the meantime, for those who get heebie-jeebies just thinking about bugs, it's probably good to remember that insects are crucially important to us in myriad ways, both “good” and “bad.” Insects pollinate our crops and also sometimes destroy them. They control disease but also spread it. When ecosystems are in balance, insects check each other's populations. And even those destructive skin beetles perform a crucial service: They are natural recyclers, part of life's great dust-to-dust cycle.
To give a sense of how wondrous and important the insect world is to California, and to Berkeley researchers, we asked Pete Oboyski to introduce us to a dozen or so species from the Essig's vast collection, beginning with the cutest of all, the ladybugs—which, at the risk of being pedantic, we have to point out are not really bugs at all.
The Lady Bug
The convergent ladybug, or more properly, convergent lady beetle(Hippodamia convergens),is a familiar sight in the Berkeley Hills, where large clusters of them often overwinter or carpet the forest floor. H. convergens is commercially gathered from large aggregations found in the Sierra Nevada for use as biological control—particularly of aphids, which are the beetle's primary food source. Oboyski says agriculture has changed the behavior of these beetles over time. Before water was diverted for agriculture, he explains, the aphid populations would naturally decline in the summer as vegetation dried up. In response, the lady beetles would move up into the hills. Now they tend to stay all season due to an abundance of food. “We've completely changed the dynamics of these beetles to a large part because of agriculture, which is supporting things they feed on.”
The Crane Fly
The ubiquitous crane flies(Tipulidae) are doubtless among the most misunderstood insects found in our homes. Many of us mistake them for giant mosquitoes; others believe the flies prey on the mosquitoes, calling the flies “mosquito hawks” and “mosquito eaters.” In reality, says Oboyski, “they don't feed at all as adults. And they don't live long. But they're food for an amazing number of vertebrate animals—bats and birds and lizards and anything else that can catch one will eat it. So while [the crane flies] come out in abundance, like all those baby sea turtles heading for the ocean, only a couple of them actually survive to reproduce.”
The Glassy-Winged Sharpshooter
The glassy-winged sharpshooter (Homalodisca vitripennis) is a large leafhopper native to the American southeast. It is of special concern in California because the species carries a plant pathogen in its system that triggers a grapevine blight called Pierce's disease. The invasive H. vitripennis also made its way to Tahiti where, lacking any predators, the population exploded, leading to something called “the rain effect.” Oboyski explains, “They're sapsuckers, so they're drinking lots and lots of sugar water to get little bits of nitrogen, which they really need to build proteins. But most of that sap is just water, and so they need to pee.” In Tahiti, the sugar-water excrement coming from the trees was often so thick that it was like a rain shower. Luckily, researchers from UC Riverside were able to introduce a parasitic wasp to rein in what locals had taken to calling the “pissing fly.”
Probably no household pest is quite as repugnant to us as the bedbug (Cimicidae), which feeds on our blood at night. Not so long ago, Oboyski notes, bedbugs were just a fact of everyday life. “It wasn't until World War II and the chemical revolution and DDT that we were on the verge of chemically controlling them, and they disappeared for a few decades.” Now, however, they're resistant to DDT and other chemicals and are making their resurgence, much to the alarm of hotels and their guests. “I get calls from people who want to sue a hotel because they found bedbugs in their room. And the bedbugs are completely harmless. They aren't carrying any disease; there's just this connotation of being unhygienic. Whereas mosquitoes actually do carry diseases—but would anyone sue a hotel because they got bit by a mosquito? Probably not.”
The Tarantula Hawk
When it comes time for the female tarantula hawk, the giant in the family of so-called spider wasps (Pompilidae), to lay its egg, it engages in an epic struggle with a tarantula. They're pretty evenly matched, observes Oboyski, and the stakes couldn't be higher. “If the wasp loses, it gets eaten; but if it wins, it paralyzes the spider with its sting, drags it off and buries it, and then lays its egg in [the spider].” As the larva develops, it feeds on the tarantula, carefully avoiding the host's vital organs so as not to kill it off. Although tarantula hawks are considered fairly docile, their sting is said to be extraordinarily painful. Arizona-based entomologist Justin Schmidt, best known for his “sting pain index,” calls the sensation “instantaneous, electrifying, excruciating, and totally debilitating.” Schmidt's advice: Lie down and scream.
The Gall Wasp
On the other end of the size spectrum, the diminutive gall wasp(Cynipidae) grows its larvae in a plant growth called a gall. “Each gall is very specific to the wasp that laid it,” explains Oboyski. “It's the plant that grows the tissue, but somehow the wasp is telling the plant to grow this exact shape for [the wasp's] larvae. Along with the egg, they're introducing some enzymes that are turning on genes inside the plant.” But the story doesn't end there. “As if that's not enough, there are other wasps that want to lay their eggs there, too. So now you have interlopers. And then there are things like parasitic wasps that know there's some nice squishy larvae in there, and they insert a tube into the gall and lay their eggs inside those larvae. Then there are hyperparasitoids that lay their eggs inside the larvae that are inside the other larvae. And then there are things that feed on the galls outside. So a whole community arises from this tiny little wasp that caused the plant to swell up.”
The Carpenter Bee
Like termites, carpenter bees also burrow into wood. The valley carpenter bees (Xylocopa varipuncta) are named for California's Central Valley and are the state's largest native bees. Unlike honeybees, which were brought to the Americas from Europe, carpenter bees don't generally sting. Like honeybees, they're good pollinators. Due to the much-publicized colony collapse disorder, in which vast numbers of worker bees simply vanish from a honeybee colony, Oboyski says there has been a spike of interest in native pollinators. “We're not sure what's going to happen with honeybees, so the thinking is we'd better hedge our bets and see how we can get our native bees to provide the same services.”
The Africanized Bee
Another bee that has had a lot of media attention is the Africanized bee, or “killer bee,” although less so lately. Oboyski says the Africanized bees are now hybridizing with our European honeybees, with mostly positive results, allaying earlier hysteria about wild swarms of killer bees attacking school children. “This fear that we're now going to have this more aggressive bee here is probably true, but the Africanized genes are mellowed out by the European genes.” What's more, he says, “the Africanized bees also bring resistance to some pests, like the mites that feed on the European bees. So it's actually improving their health.”
As for colony collapse disorder, Oboyski says it's still a bit of a mystery. “The leading suspects now are these neonicotinoid pesticides that [the bees] seem to be very sensitive to. But in my opinion, it's not likely to be a single factor at play. It's a species we've been managing intensely for a very long time. … They're boxed up one night in an almond orchard in California, and they wake up the next day in an apple orchard in Michigan, and it's very stressful. Neonicotinoids may just be the last straw.
“But there's been some really entertaining ideas of what happened to the bees. I remember someone saying they'd been taken up by the Rapture. They were pointing to the fact [the bees] disappear. It's not like you see a bunch of dead bees around. To me, that's not surprising because, you know, they're food. If there's a dead bee somewhere, something's going to eat it.”
The Bark Beetle
California pine forests are being laid to waste as tens of millions of trees succumb to an epidemic of bark beetles, including mountain pine beetles and other relatives of the Scolytidaefamily of weevils. It may sound like an alien invasion, but it's not. Says Oboyski, “The bark beetles that are causing the problems are actually native here, and it's not that they've changed over the years. It's the way we've managed landscapes that has changed,” particularly in terms of clearcutting and fire suppression. Those practices, he says, have resulted in large monocultural stands and old decadent trees that are more susceptible to pest invasion than a “young, vigorous forest that's constantly refreshed by fires.” And, of course, drought has been an aggravating factor. “These beetles only attack stressed trees. If the tree is healthy, they get ‘pitched' out by the tarry sap they produce. But in a stressed tree that's attacked by lots of beetles at the same time, there's not enough pressure behind that pitch to push the beetles out.”
Bark beetles only infest live trees, whereas termites(Termitoidae) come in long after the tree is dead. And unlike the bark beetles, which aren't feeding on the tree but rather using it to make their nests, termites are actually eating it. To accomplish that, however, they need help. “Termites can't actually digest wood themselves, but they have this gut fauna inside that can actually convert the lignin of the plant into digestible food.” The symbionts reside in the parts of the termites' gut that get shed when they molt, adds Oboyski. “That means every time that they molt, they lose their ability to digest wood. So they have to do a fecal transfer to get them back again. So they will feed on the feces of other termites to get those bacteria back.”
The Xerces Blue
The Xerces blue(Glaucopsyche xerces), like the California Golden Bear, no longer exists. Endemic to the erstwhile dunes of San Francisco's Sunset District, the powder-blue gossamer-winged butterfly was presumably done in by urban development. Showing the Xerces at the Essig, Oboyski says, “It's rare to be able to document extinctions in the insect world, but this is one we're fairly certain about.” He calls this butterfly the “poster child of invertebrate extinction.” The Xerces blues were part of a family of little blue butterflies, some of which “have ridiculous relationships with ants. The ants actually take them into their colonies and feed them and take care of them.” It seems the caterpillars release pheromones that smell like the ants. The last known Xerces blue was netted by Berkeley alumnus and later UC Davis entomologist W. Harry Lange '33, in the Presidio on March 23, 1941. “I always thought there would be more,” he lamented later. “I was wrong.”
Posted on Thursday, September 28, 2017 at 11:12 AM
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.