Whitebark pines at Crater Lake and Lassen: about half carry blister rust

About half of the whitebark pines sampled in Crater Lake and Lassen Volcanic National Parks were infected with white pine blister rust, a disease most infected trees do not survive. The finding comes from a study of three years of monitoring by the National Park Service's Klamath Network, written up in the journal Forests by its scientists and a graduate student who led the field crew, and summarized in a Park Service article from fall-winter 2019.

Why the tree matters

Whitebark pine is called a keystone species of high-elevation forests in the West. Its nutritious seeds feed bears and other wildlife, its branches shade snow and prolong the melt, and its roots hold thin, rocky subalpine soil. But it is in severe decline across its range, from mountain pine beetle, blister rust, fire suppression and climate change. With the Pacific Northwest projected to become warmer and drier, managers of high-elevation parks face a complex problem.

How the study worked

The paper, "Whitebark Pine in Crater Lake and Lassen Volcanic National Parks: Assessment of Stand Structure and Condition in a Management and Conservation Perspective," asked two questions: what the current status of whitebark pine is in the two parks, and how its stressors interact to influence survival. Between 2012 and 2014 the team collected data in thirty 50 by 50 meter plots in each park, recording tree species, size and health and signs of blister rust or beetle attack, and combined them with outside climate data. The monitoring is part of the network's long-term tracking of whitebark pine as a vital sign of each park's health.

What it found

• About half of the sampled trees in each park, around 55 percent, had blister rust. That was somewhat surprising in Lassen, where little rust had been seen before.
• In both parks, whitebark pines made fewer cones when crowded by other trees, mainly mountain hemlock, which seems to have spread into the subalpine zone because of fire suppression, climate change or both.
• At Crater Lake, trees in drier, water-stressed areas were more likely to have rust and less likely to have cones.
• At Crater Lake, trees with rust were more likely to be attacked by mountain pine beetle, so the pest and the pathogen together made matters worse.

Mountain hemlock crowding a lone whitebark pine at Lassen Volcanic National Park. NPS photo.

What managers could do

The authors' findings fit range-wide conservation principles already identified, and add detail for these parks.

1. Promote resistance to blister rust. Other studies estimate only about 1 percent of whitebark pines resist the disease, so the high infection rate shows how serious it is. The article gives genetic trials at the Dorena Genetic Resources Center in Oregon as an example of work to find resistant types and grow their seedlings, though the paper does not mention it.
2. Conserve genetic diversity. The link between dry sites and rust at Crater Lake raises questions, such as whether to plant seedlings in wetter areas and whether to protect trees surviving on drier slopes just outside the park.
3. Protect declining seed sources. The study recommended verbenone, which mimics the pheromone beetles use to tell each other a tree is full, at both parks to protect cone-bearing trees. It is not used at Lassen now because beetle attack there has been sparse and most stands are in wilderness with more restrictions, but the same pest-pathogen pattern could develop there.
4. Restore. Because competition lowered cone production at Crater Lake, the authors favor reducing it with fire (natural or prescribed) or mechanical thinning, concluding that cutting competition looks important to conserving the species in both parks.

White pine blister rust (Cronartium ribicola) cankers on a whitebark pine, showing the yellow-orange spores of the fruiting bodies. NPS photo.

Sources

• National Park Service, "Making Sense of Monitoring Data: Whitebark Pine Conditions in the Southern Cascades" (article by Sonya Daw of the Klamath Inventory and Monitoring Network, adapted from The Klamath Kaleidoscope newsletter, Fall-Winter 2019, by Jessica Weinberg McClosky), about the paper in the journal Forests by NPS Klamath Network scientists and a graduate student at Humboldt State University; the paper's plot figures are left out here; rewritten in hubnx's own words.