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).