Forest Explorer Newsletter - April 2024
Effective beginning 5/30/2025
This website, and all linked websites under the control of the agency, is under review and content may change.
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Bark Beetles and Tree Mortality |
 The occurrence of high-severity wildfires and several multi-year droughts have played important roles in California tree mortality in recent decades. However, it’s the increase in opportunistic arthropods known as bark beetles that have helped create the compound disturbance wave plaguing vulnerable trees. With hundreds of native species in North America alone, the bark beetle isn’t all bad. These tiny insects play a key role in nutrient cycling and ecological succession (changes an ecosystem undergoes over time). However, less than a dozen species of bark beetles are known to have outbreaks that can result in large-scale tree mortality in California. Key species include the western pine beetle in ponderosa and coulter pines, the mountain pine beetle in ponderosa, lodgepole, sugar and whitebark pines, the Jeffrey pine beetle in Jeffrey pine, and the fire engraver in white and other true firs. As warming and droughts reduce available water, and wildfires damage trees, they inhibit natural tree defense mechanisms, allowing for beetles to colonize trees with greater ease. 
Some bark beetles have complex chemical communication systems, utilizing various pheromones to attract or inhibit additional bark beetles. Bark beetles chemically communicate as they colonize new trees, boring through the outer protective bark into the inner bark to mate and lay their eggs. The subsequently hatching larvae feed on the phloem, or the transport tissue for photosynthesis products, like sugars. Adults and larvae bore through the phloem, creating distinct patterns known as galleries (see left image). Since multiple bark beetle species may colonize the same species of tree, such as ponderosa pine, galleries are one way of distinguishing the amount of bark beetles.
Options for addressing bark beetle infestations vary from physical (e.g., removal of infested trees) to chemical (e.g., insecticide applications). At the Pacific Southwest Research Station, Research Entomologist Dr. Chris Fettig has examined the use of semiochemicals to reduce levels of tree mortality caused by bark beetles. Semiochemicals are the natural chemicals produced by living organisms, or in this case, the pheromones emitted by bark beetles and volatiles released from nonhost trees. Dr. Fettig’s work seeks to identify the key pheromones produced by the most aggressive bark beetle species, and to use this and other information to develop effective control strategies. 
One such product that has been developed in collaboration with scientists in academia, Forest Service R&D, Forest Service State, Private & Tribal Forestry, and private industry is SPLAT® Verb, which utilizes verbenone, an antiaggregant pheromone produced by several species of bark beetles including mountain pine beetle and western pine beetle, among others. When SPLAT® Verb is applied to trees, bark beetles perceive the scent as a signal that the tree is full and can no longer accommodate more beetles. This work has far-reaching implications, with studies into its use underway for European spruce bark beetles in Norway, spruce forests in Germany, and for ambrosia beetles in native ʻōhiʻa trees in Hawai’i. Verbenone isn’t going to solve tree mortality on its own. However, when paired with other forest management practices, SPLAT® Verb shows success in reducing beetle aggregation and giving land managers the time to formulate other management strategies.
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Around the StationInteractive Fire Map for the Western Pacific |
 The Pacific Southwest Research Station and the Hawaiʻi Wildfire Management Organization partnered to create online interactive maps showing burn areas from wildfires on islands in the Western Pacific including Guam, Palau, Yap State (Federated States of Micronesia), and the Commonwealth of the Northern Mariana Islands (Saipan, Tinian, and Rota Islands).
Map Link (External Link) |
Webinars & Events |
Previous Webinar March 27th, 2024
Dr. Eric Knapp Effectiveness of Thinning and Prescribed Fire Treatments in the 2021 Antelope Fire Lunch and Learn Webinar SeriesThe Lunch and Learn series shares our research with end users and connects PSW with forest and wildland managers.
Next Webinar: April 24th, 2024 1 PM PST/11 AM HST Dr. Chris Fettig (PSW) & Dr. Kylle Roy (R5) Research Entomologist & Forest Entomologist
A Scentsible Approach: Using Chemical Ecology to Manipulate Insect Populations and Protect Host Trees in California and Hawaii
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 Get Interactive with National Forest Trends in CAThe USDA Forest Service Pacific Southwest Region (Region 5) is publishing its first interactive website on social, economic and ecological trends for national forests in California. The site is packed with data dashboards, interactive maps, descriptive trend summaries, tables and figures.
Contact: Stephanie Coppeto (stephanie.coppeto@usda.gov)
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 SCIENCEx Soils WeekMay 6th - May 10th will be SCIENCEx Soils week. Forest Service researchers will cover a variety of topics pertaining to how soil science can support forest management, resilience, and forest products.
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Station News |
 Through the FireSometimes out of adversity comes wisdom. That was a lesson Pacific Southwest Research Station Ecologist, Eric Knapp, learned after the 2021 Antelope Fire tore through long-term research plots in northeastern California.
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 Mighty Mangroves: Forest Service Researchers Help Conserve Coastal Guardians in MicronesiaMangroves help curb climate change, create wildlife habitat, and protect communities. And Pacific Southwest Research Station ecologist Rich MacKenzie’s mission is to promote their conservation. MacKenzie’s research focuses on mangroves in Micronesia.
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 California Communities Share their Vision of Wildfire Recovery in Mendocino National ForestCalifornia’s 20 million acres of national forests support ecosystems and sustain communities. But more frequent and severe wildfires are threatening forests in the nation’s most biodiverse state. The U.S. Forest Service's Pacific Southwest Research Station is collaborating with the Pacific Southwest Region's ecology program.
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 Christian Giardina Appointed New Director of Institute of Pacific Islands ForestrySince the 1950s, the Pacific Southwest Research Station’s Institute of Pacific Islands Forestry (IPIF) has served Hawaiʻi and the U.S. Affiliated Pacific Islands to meet scientific needs of resource stewards. Based in Hilo, Hawaiʻi.
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External Media Yes, beavers can help stop wildfires. And more place in California are embracing them A vast burn scar unfolds in drone footage of a landscape seared by massive wildfires north of Lake Tahoe. But amid the expanses of torched trees and gray soil, an unburnt island of lush green emerges. The patch of greenery was painstakingly engineered.
Read more: LA Times (External Link) |
Publication Highlight |
 Keeping up with the landscapes: promoting resilience in dynamic social-ecological systems
Manley, Patricia; Long, Jonathan; Scheller, Robert. 2024. Keeping up with the landscapes: promoting resilience in dynamic social-ecological systems. Ecology and Society. 29(1): 3. |
More PSW Publications via Treesearch
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Fact and Trivia Corner Scroll to the very bottom for the answers. |
Pacific Southwest Research StationThe Pacific Southwest Research Station (PSW) was founded in 1926 as a part of the Research and Development branch of U.S. Forest Service. Since its inception, PSW has expanded to serve California, Hawai'i, and the US-affiliated Pacific Islands. PSW develops and delivers science-based information, technologies, and applications to help people make informed decisions about natural resource management, conservation, and environmental protection. |
Trivia Answers
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