By Lorelle Sherman, OSU Extension Forester

If you’ve noticed dead twigs and small branches scattered throughout the canopy of your Oregon white oak, especially near the tips of branches, you’re seeing what’s known as branch flagging. This phenomenon is noticeably more severe in certain years and in certain locations and is currently causing alarm throughout the mid-Willamette Valley.

This story starts with an insect smaller than a grain of rice and a squirrel with a taste for larval protein.

Gall wasps and their galls

Gall wasps (family Cynipidae) are highly specialized insects associated with gall formation on oak trees. The adult gall wasp lays its eggs into the tissue of an oak twig, leaf, or bud, where the egg will hatch into a hungry larva. Larval feeding on the plant tissue triggers swelling of the plant tissue. The result is a gall — a swelling or growth made from the tree’s own tissue, which forms a protective chamber for the developing larvae. Eventually the larva will pupate into an adult which exits through the gall to start the cycle over again.

Galls can be variable in size, structurally complex, and species-specific, often serving as microhabitats for other insects. Oaks, including our Oregon white oak, are common hosts to gall wasps and other gall-forming organisms. While most galls are harmless, repeated or clustered twig galls can girdle small branches, effectively cutting off the flow of water and nutrients. Over time, this causes localized dieback — branch flagging — that’s particularly noticeable in the summer.

The species at play in our Oregon white oaks is the oak twig gall wasp (Bassettia ligni). The Oregon white oak has evolved with gall-making insects like the oak twig gall wasp and is quite adapted to this cycle of crown thinning. Branch flagging is cosmetic and oaks will rebound from it in subsequent years. However, it is unclear how changing environmental factors like hotter and more frequent droughts will interact with the oak twig gall wasp.

Western gray squirrel and Oregon white oak

Our native Western gray squirrel (Sciurus griseus) is strongly associated with oak woodlands in western Oregon. Western gray squirrel diet includes acorns, catkins, nuts, berries, aphids, fungi, insect larvae, and other protein-rich plant materials. Oregon white oak is the only acorn-producing species across much of the Willamette Valley and it has highly variable acorn production from year to year. Oregon white oaks will produce an incredibly abundant acorn crop in one year – known as a mast year – and hardly produce any for several years after. This is a major limitation on oak-associated wildlife who depend on acorns as a food source. During mast years, squirrel populations will increase due to the abundant protein-rich food source. Failure of Oregon white oak to produce acorns can have serious impacts on squirrel populations.

If you have Oregon white oak on your property, you may have noticed an incredible abundance of acorns two years ago, which means we had a mast year that may have supported an increase in squirrel populations.

All these squirrels gotta eat!

Western gray squirrels discovered long ago that certain galls house protein-rich wasp larvae. In the Willamette Valley, this is the oak twig gall wasp! To access this hidden food source, they strip bark from infested twigs, removing cambium tissue in the process. This debarking behavior can compound damage caused by the galls themselves. It increases branch mortality and may contribute to more severe branch flagging in some trees.

Should we be concerned?

Despite the visible damage, Oregon white oaks (Quercus garryana) are remarkably resilient. Branch flagging due to gall formation and squirrel foraging is a natural and cyclical process that these trees have evolved with over millennia. Whether it’s an increase in squirrel populations, or an increase in gall wasps due to a mild La Nina event last year, we can be sure of two things. First, branch flagging of Oregon White Oaks in the mid-Willamette Valley is more severe than usual this year. Second, branch flagging is an eye sore (not a sign of mortality) that can be dealt with by calling an arborist to remove dead branches if desired.

ODF resource on oak pests: https://www.oregon.gov/odf/documents/forestbenefits/oak-pests.pdf

Sources

• Sciurus griseus
• Oak Gall Wasp – PNW Pest Management Handbook
• Oregon White Oak in the Willamette Valley… some in your face issues

By Lorelle Sherman, OSU Extension Forester

Becoming a birdwatcher

Birdwatching is the perfect gateway to learning more about the ecosystem around us. Birds are excellent indicators of ecosystem condition because they respond to ecological change. If you plant native berry-producing bushes in your backyard, you may be visited by a suite of fruit-eating birds, like robins and bluebirds. If a wildfire burns through your forestland, you may discover new species of woodpeckers and flycatchers that utilize the influx of dead wood and open space. If you put a nectar feeder up… hummingbirds!

Through birdwatching, we can start to recognize the ways different species and resources are interconnected through the ecosystem services birds offer including seed dispersal, pollination, and insect control. Birds play a significant role in seed dispersal by both passively and actively transporting seeds, primarily through frugivory (eating fruits) and seed-caching behaviors (saving fruits for later). They digest the fleshy part of the fruit, leaving the seeds intact, which are then excreted often farther from the plant than would occur by wind dispersal. Some seeds even have adaptations to stick to bird bodies so they can be dispersed over long distances during flight. Recent studies have confirmed that several songbirds in Oregon (orange-crowned warbler, yellow warbler-rumped warbler, etc.) provide pollination services while foraging in flowers. The diet of birds ranges widely, but some species specialize in eating insects. Even species that lean towards herbivory as adults will feed their nestlings insects to ensure proper nutrition during rapid nestling growth. Collectively, bird populations can act as a control on insect populations and enhancing bird communities near crops has been a pest control strategy implemented in agriculture.

Birdwatching also allows us to key into changes in habitat over time, year-to-year variation in weather, and long-term changes in climate. In order to do this, we must recognize that there are resident species which remain local year-round, and migratory species which fly between breeding habitat and overwintering habitat. Resident bird populations can act as indicators of local weather patterns and ecosystem health, so monitoring their populations is valuable for public lands, local parks, and even our backyards (more on this later). Migratory bird populations can clue us into shifting weather patterns over time and large-scale changes to the landscape. For example, if warmer temperatures happen earlier each spring, we may see a mismatch in timing between the return of flower-feeding songbirds and the flowering of plants.

If you are new to birding, I recommend spending an hour each morning sitting in your backyard or favorite park with a notebook, field guide to western bird species, maybe a pair of binoculars, and possibly an identification app on your phone. Take notes on the different sounds you’re hearing. Are they long and melodic? Deep and guttural? Short, high-pitched chips? Practice taking notes on any birds you see. What color are the back feathers? The belly feathers? Any white bars on the wings? A long or short bill? How long is the tail? Take notes on the behavior of the bird. Where in the environment is it perched or flying? Is it bobbing its body up and down or flicking its tail? In my opinion, taking notes is integral to becoming a better birder. We are lucky to be birdwatchers during the rise of user-friendly technology that brings birding right to our fingertips. Websites and apps on our mobile phones are incredibly helpful and can be a tool in addition to your trusty notebook.

Next level birdwatching

The right app on your cell phone can help you identify species, log your bird sightings, and even connect with fellow bird enthusiasts. Here are a few of my favorite free technological resources:

• Merlin Bird ID – Developed by the experts at the Cornell Lab of Ornithology, this app has several functions. The Bird ID feature guides users through a series of questions to narrow down the possibilities based on size, color, and behavior, offering a shortlist of potential matches The Sound ID feature records and analyzes the bird songs and calls around you providing real-time suggestions for the birds it detects. The app includes regional bird packs, has offline functionality, and is integrated with eBird allowing users to contribute their sightings to the global eBird database.
• eBird – Also created by Cornell Lab, eBird is a global online database and citizen science project where birders log their bird sightings, share data with others, and explore birding hotspots and species information. eBird allows users to track their life lists, target species, and create alerts for rare sightings. It is used by birders of all levels, researchers, and conservationists to understand bird populations, track migrations, and inform conservation efforts.
• iNaturalist – This joint initiative by the California Academy of Sciences and the National Geographic Society is based on crowdsourcing of observations and identification. While it’s not solely focused on birds, it’s a powerful tool for logging bird sightings alongside all kinds of flora and fauna. You can upload photos, get help identifying species from a global community of naturalists, and contribute to scientific research projects. It’s especially useful for birders who are also interested in the broader ecological context of their observations.
• BirdNET – BirdNET is another option for identifying birds based on their songs and calls. You simply record the sound around you, and the app processes it to identify likely species. It’s a powerful tool, especially when birds are hard to spot but easy to hear. Great for passive listening or nighttime birding.

Becoming a community scientist

Remember how birds can act as indicators of ecosystem function and health? We, as birdwatchers, can provide valuable information to researchers through our observations of birds. While traveling to the Oregon Coast or Malheur National Forest may be more your style, we can submit observations from our backyards, neighborhood parks, or favorite greenspaces. eBird and Merlin Sound ID have handy resources for birdwatchers who would like to ensure their observations are available for scientific research. Data contributed by community members has been used to create accurate range maps for species and track species population trends over time. This is science!

If you’d like to get involved in an organized community science effort, here are a few ways to contribute:

• Project FeederWatch – This survey occurs every November-April in an effort to capture winter bird abundance and distribution to the fine scale of weekly changes. This can be done from your kitchen window with a field guide in hand if you are strategic about feeder placement. All you have to do is select your site, install a bird feeder, and identify and count birds! There is a small fee for participation.
• Audubon’s Christmas Bird Count – This survey is the nation’s longest-running community science bird project and operates annually from December 14-January 5. CBC counts are a group effort and involve walking pre-determined routes within a designated 15-mile diameter circle to get complete census data of all birds within the circle. This is a great way to learn because beginners are paired with at least one expert. Participation is free.
• North American Breeding Bird Survey – If you are advanced in your bird identification skills, you may choose to get involved with a local Breeding Bird Survey (BBS) where pre-determined routes are surveyed by volunteers. In order to participate, you will need the ability to identify all breeding birds in the area by sight and sound and you will need to complete a methodology training program. The data collected is rigorous and therefore highly valuable to science.

Whether you choose to contribute to science through independent observations or through an organized effort, you can contribute to data gathering on a scale once unimaginable. The data is used by scientists to reveal how birds are affected by habitat loss, disease, climate, etc., and guides conservation efforts, including habitat restoration, species protection, and mitigation of threats to bird populations. Participation can be as simple as watching a feeder or as complex as running a BBS route, but there’s no better time to get started than today!

by Lorelle Sherman, OSU Extension Forester

What do Oregon White Oak, Truffles, Rodents and a Golden Retriever have in common?

Oregon white oak (Quercus garryana) savanna and woodland were once widespread in the Willamette Valley but are now considered endangered habitats¹. The decline of both has been attributed to agricultural expansion, fire suppression, and invasive species. The Oregon white oak is a biodiversity workhorse and has been providing habitat for hundreds of wildlife species for millennia². This species has spanned the test of time because of its drought tolerance and fire resiliency, but also because it can handle seasons with high rainfall. However, even the persistent Oregon white oak needs a hand in long-term survival.

Oak trees, like many other trees in our region, depend on partnerships with ectomycorrhizal fungi for enhanced nutrient and water uptake. In this partnership, the fungi increase the uptake of water and nutrients like phosphorus, nitrogen, and potassium, by attaching to and extending the tree’s root system. Through photosynthesis, the tree supplies the fungi with carbohydrates. The Oregon white oak forms these partnerships with over 40 different species of fungi³, many of which are known as truffles!

Truffles are a type of mycorrhizal fungi that develop fully underground. While mycologists may disagree, these spherical fruiting bodies are not nearly as showy as the fungi that produce the colorful and often unusual above-ground fruiting bodies currently dazzling popular culture. What truffles lack in appearance, they make up for in smell. More on smell later…

Truffles uniquely rely on animals for spore dispersal. This can happen in two different ways: 1) they are kicked to the surface by an elk or deer passing by, or 2) they are consumed by a rodent, bear, or whatever else fancies a fungal treat. In addition to occupying an important partnership with oak trees, truffles also serve as a major food source for wildlife.

Rodents: the unwitting truffle farmers

Rodents, such as mice and voles, consume large amounts of truffles and pass the spores through their systems unscathed. These animals are highly attuned to the scent of truffles, digging them up and consuming them as a food source. In the messy process of eating, they spread fungal spores across the forest floor. More remarkably, the spores of truffles are still viable after passing through the rodent digestive system. Rodents love eating and defecating truffles so much, they may actually aid in the habitat expansion and seeding survival of Oregon white oak in our savannas and woodlands! Oak acorns are often carried away from the parent tree by birds or squirrels and often land outside the parent tree root zone, meaning no access to mycorrhizal fungi. One hypothesis for oak seedling survival in these cases is that rodents are dispersing incredible amounts of truffle spores through defecation while running from tree to tree.

Enter Rye, the Golden Retriever

There are hundreds of native truffle species in Oregon, but only a handful are of culinary value (Tuber oregonense, T. gibbosum, Leucangium carthusianum, Kalapuya brunnea). While we know a bit about these culinary species from only very recent DNA sequencing and ecological research, they are not the species found in Oregon white oak fungal partnerships. There’s an entire new world of truffle species that associate with oak trees and we have barely scratched the surface. In fact, we’ve barely scratched the surface on fungi in general!

Meet Rye the golden retriever. When Rye is happily wagging his bushy tail, he smells something interesting under the soil’s surface. Rye is Heather Dawson’s truffle biodiversity dog, which means he surveys all species of truffles instead of being limited to the few species of culinary and economic value. Heather Dawson, a PhD candidate at University of Oregon, is studying the diversity of Oregon white oak associated truffles and the dietary preferences of truffles amongst our native small mammal community.

Rye is Heather’s second truffle dog and while he’s been trained with culinary truffles, he continues to expand his smell library and frequently calls attention to new smells. Heather wondered if he gets bored of the common truffle species at a site and starts keying into new smells, which range from “canned corn and tomato paste” to “burning brakes” to “sunscreen”. Some of the samples Rye has collected will likely turn out to be undescribed species and will help to unravel the story of truffles in the Willamette Valley.

The Bigger Picture

While the rodents undoubtedly recognize the array of oak associated truffle smells we are only beginning to learn about, Rye and Heather are doing the work to catch up. Heather plans to collect small mammal fecal material by setting up live traps and humanely capturing and releasing them, noting their species. Fungal spores in the fecal material will be DNA sequenced along with Rye’s truffle treasures. Heather also plans to collect and DNA sequence mycorrhizal fungi from soil cores and root samples from her Oregon white oak savanna and woodland sites.

In order to protect Oregon’s endangered oak savannas and woodlands, we must understand all parts of the ecosystem. Most oak ecosystem research has focused solely on plants and animals, with little knowledge of what role fungi plays in maintaining this charismatic system. Heather and Rye’s work will catalog truffles that support a biodiverse landscape, home to hundreds of birds, insects, amphibians, and reptiles.

Sources

1. Vesely, D. G., & Rosenberg, D. K. (2010). Wildlife conservation in the Willamette Valley’s remnant prairies and oak habitats: A research synthesis. Interagency Special Status Sensitive Species Program, US Forest Service/Bureau of Land Management, Portland, OR.
2. Hosten, P. E., Hickman, O. E., Lake, F. K., Lang, F. A., & Vesely, D. (2006). Oak woodlands and savannas. Restoring the Pacific Northwest: the art and science of ecological restoration in Cascadia, 63-96.
3. Frank, J., Barry, S., Madden, J., & Southworth, D. (2008). Oaks belowground: mycorrhizas, truffles, and small mammals. In: Merenlender, Adina; McCreary, Douglas; Purcell, Kathryn L., tech. eds. 2008. Proceedings of the sixth California oak symposium: today’s challenges, tomorrow’s opportunities. Gen. Tech. Rep. PSW-GTR-217. Albany, CA: US Department of Agriculture, Forest Service, Pacific Southwest Research Station: pp. 131-138 (Vol. 217, pp. 131-138).