Finding whitebark pines that can resist blister rust

Some whitebark pine seedlings in a field in Cottage Grove, Oregon, turn brown and some stay green, and the difference is the point. The brown ones show lesser resistance to white pine blister rust, the green ones greater, and researchers are looking for trees with natural resistance to it. This National Park Service article, adapted from the Klamath Network's newsletter (Fall-Winter 2017 issue, updated 1-3-2023), explains how the search for resistant trees works and what parks add to it.

Whitebark pine seedlings inoculated with the fungus that causes blister rust: green ones show greater resistance, brown ones lesser. Photo: USFS/R. Sniezko.

A tree under several attacks

The whitebark pine grows in harsh subalpine climates. Its cones feed wildlife with nutritious seeds, its roots stabilize thin rocky soil, and its shade prolongs snowmelt. White pine blister rust, a disease caused by the nonnative fungus Cronartium ribicola, and deaths from the mountain pine beetle have taken a toll. In 2011 the US Fish and Wildlife Service declared the tree a candidate for listing under the Endangered Species Act, and a decision was expected in 2019. An update in the article says the Service listed it as Threatened on January 17, 2023.

White pine blister rust cankers. Image from the National Park Service's page.

Federal agencies, university scientists and conservation organizations have taken a four-part approach:

• Research the tree's ecology, genetics (including natural rust resistance) and vulnerability to stressors.
• Monitor whitebark pine, blister rust and mountain pine beetles across the tree's range.
• Protect stands by placing pheromones on trees to prevent beetle attack, clearing debris from under trees to reduce fire risk, and pruning branches that have rust cankers.
• Restore the tree by planting rust-resistant seedlings and by promoting natural processes such as wildland fire, which opens ground for seedlings.

Finding a resistant tree takes up to seven years

The US Forest Service's Dorena Genetic Resource Center began researching blister rust in five-needle pines in 1966; its whitebark pine work began in 2002 and has reached the point of planting rust-resistant trees in a handful of parks and national forests. Crater Lake National Park staff joined the first trials and began sending cones from healthy, older trees to Dorena in 2003. The whole process costs $1000 a tree, not counting cone collection.

1. In rust-infected areas, pick healthy whitebark pines with no sign of rust, the trees most likely to have some genetic resistance.
2. Protect them from beetles with verbenone, a mountain pine beetle pheromone that tells beetles the tree is already full of them.
3. Cage the developing cones in midsummer to keep out Clark's nutcrackers.
4. In early October, remove the cages, harvest the cones, extract the seeds and grow them at Dorena.
5. At two years old, infect the seedlings with blister rust and monitor them for five more years. Often only a small percentage of the batch is left alive.
6. Plant the most resistant survivors, graded A to F, in areas targeted for recovery.

Seedlings before planting at North Junction (top) and after planting at Rim Village in Crater Lake National Park (bottom). Image from the National Park Service's page.

At the Rim Village parking area in Crater Lake, 87% of the planted seedlings had survived as of 2016, which the article credits partly to the lack of hungry gophers there. A later update gives 75.9% as of 2022.

The monitoring side

While Dorena handles research and Crater Lake staff protect and restore trees, the Klamath Network contributes through long-term monitoring; whitebark pine is one of its "vital signs" of park health. Each summer a Network botanist and an intern from the host campus, Southern Oregon University, monitor whitebark pines at Crater Lake and Lassen Volcanic National Parks. They count seedlings, measure diameters, document dead trees and record evidence of blister rust and mountain pine beetles. Some of the data feeds a regional dataset kept by the US Forest Service; locally it gives park scientists a regular checkup.

Sources

• National Park Service, Klamath Inventory and Monitoring Network, article by Sonya Daw, "Boosting Natural Selection: A Conservation Tool for the Whitebark Pine" (https://www.nps.gov/articles/000/boosting-natural-selection-a-conservation-tool-for-the-whitebark-pine.htm), adapted from the Klamath Kaleidoscope newsletter. One photo of a named intern is left out.
• National Park Service; rewritten in hubnx's own words.