CRATER LAKE NATIONAL PARK, Ore. — Scientists are working to protect the iconic whitebark pine trees that grow along the rim of Crater Lake from a deadly invasive fungus known as white pine blister rust.
The disease, introduced from Europe more than a century ago, infects pine trees through spores that eventually form cankers on branches and trunks. As the infection spreads, it can girdle the tree and cut off the flow of nutrients, ultimately killing it.
Whitebark pines are one of the few tree species able to survive the harsh, high-elevation conditions around Crater Lake, which formed from the collapsed volcano Mount Mazama. The trees play a critical role in the park’s ecosystem and provide food for wildlife such as Clark’s nutcrackers.
For decades, researchers including U.S. Forest Service geneticist Richard Sniezko have studied ways to help the species survive the disease. Their work involves growing thousands of seedlings from seeds collected across the Pacific Northwest and intentionally exposing them to blister rust in controlled conditions to identify individuals with natural resistance.
Many of the seedlings die during testing, but some survive the infection. Those resistant trees are then cross-bred to produce new generations with improved defenses against the fungus.
Tree climbers collect pollen and carefully pollinate cones from resistant trees, which are protected from birds until seeds can be harvested and grown into new seedlings. The resulting trees are planted in forests across the region, including within Crater Lake National Park.
Park biologists have planted thousands of these seedlings over the past decade in hopes that they will eventually replace older trees lost to disease.
Whitebark pine was listed as a threatened species under the Endangered Species Act in 2023. In addition to blister rust, the trees face other challenges including mountain pine beetle outbreaks and climate change that is reducing snowpack at high elevations.
Despite those threats, researchers say decades of work identifying disease-resistant trees has improved the outlook for the species.
Scientists continue to monitor the planted trees over many years to see how well they survive in the wild, a process that can take decades. Researchers say the goal is to establish future forests of whitebark pine that can withstand blister rust and continue growing on the rim of Crater Lake for centuries to come.
Whitebark pine
Whitebark pine (Pinus albicaulis Engelm.) is a hardy, long-lived species. It tolerates the severe conditions found at the highest elevations of Crater Lake National Park. Whitebark pine is a foundation and a keystone species. It plays a vital role in creating and sustaining high elevation plant communities.
The seedlings of whitebark pine can tolerate full sun and are able to establish in previously tree-less areas, earning it the reputation of a colonizing or pioneer species. Once established, they improve and enhance harsh site conditions by facilitating the establishment of a diverse suite of subalpine plant and animal species. As a keystone tree, stands of whitebark pine serve important functional roles. They regulate snowmelt by shading and retaining snowpack, which also slows erosion by anchoring soils in place.
White Pine Blister Rust
Whitebark pine have been declining within the park for decades. With the introduction of a non-native pathogen, Cronartium ribicola, to western North America in 1910, the disease white pine blister rust (WPBR) has developed. It has spread throughout the range of whitebark pine with devastating results. WPBR is progressive and fatal because few whitebark pines have genetic resistance to the disease.
WPBR has five distinct stages. Two stages occur on trees as seen in photo to the right. The first image shows aecia—orange blisters which gave the disease its name. The blisters release powdery orange aeciospores that look like cheese-dust. The second image shows pycnia, spores in a sap-like fluid. The other three stages (not shown) occur on alternate hosts such as currants/gooseberries (Ribes sp.), Indian paintbrush (Castilleja sp.), and lousewort (Pedicularis sp.). The lifecycle of blister rust is very complex and may take four years to complete.
Conservation Efforts
In 2003, park botanists applied the first actions in what would become a Whitebark Pine Conservation Program. Work began by implementing a whitebark pine long-term monitoring program, and by collecting cones from whitebark pine trees. Seedlings are grown from the collected cones, and tested for resistance to WPBR at the United States Forest Service, Dorena Genetic Resource Center.
Crater Lake’s conservation program has expanded to include the planting of seedlings grown from rust-resistant “parent” trees, and annual monitoring of rust-resistant trees. Also, packets of verbenone, a bark beetle repellent, are tacked to whitebark pines that had their cones collected for rust-resistance screening . All these efforts help to maintain healthy populations and grow new stands of this high-elevation keystone tree.
In 2011, the United States Fish and Wildlife Service determined that listing whitebark pine as a threatened or endangered species was warranted but precluded by higher priority work. Whitebark pine remains a candidate species for the Endangered Species Act.
