Monitoring Whitebark Pine in the Greater Yellowstone Ecosystem: Why and How

A whitebark pine snag gives shelter to smaller surviving trees, Green River Lakes, Bridger-Teton National Forest, Wyoming, 2023. Credit: NPS / Shanahan.

The first article in the National Park Service's series Whitebark Pine Monitoring in the Greater Yellowstone Ecosystem.

A keystone of the high country

Whitebark pine (Pinus albicaulis) is an iconic tree of subalpine forests, and a keystone species there: it regulates many ecological processes and shapes biodiversity.

• A pioneer. It tolerates harsh conditions and can take hold where other trees cannot, then alter the microclimate so that species such as subalpine fir (Abies lasiocarpa) can establish.
• Food for wildlife. It has little commercial value, but its seeds are seasonal food for grizzly bears, red squirrels, Clark's nutcrackers and many small seed-eating mammals.
• One of two five-needle pines in the Greater Yellowstone Ecosystem (GYE); the other is limber pine (Pinus flexilis).

Why it is declining

High-elevation forests across the American West have changed markedly in make-up and structure over the past 50 years, and whitebark pine has declined because of:

1. White pine blister rust, caused by an introduced fungus, Cronartium ribicola. It has spread throughout the tree's range, reducing cone production and damaging young trees, and over the last century has killed many whitebark pines in the Pacific Northwest and parts of the northern Rockies.
2. The native mountain pine beetle (Dendroctonus ponderosae). Between 2000 and 2010, widespread infestations in high-elevation stands killed great swaths of mature whitebark pine forest.
3. Wildland fire. Fire has long mattered for whitebark pine's persistence, but fires are becoming more frequent and intense as snowpack melts earlier and faster with rising temperatures.
4. Climate change.

In the GYE, blister rust and beetles together have shifted populations towards smaller trees and threatened the species' reproduction and survival. Losing a foundation species like this could cause major changes in biodiversity and possibly irreversible shifts in how communities are made up. The U.S. Fish and Wildlife Service listed whitebark pine as threatened under the Endangered Species Act on January 17, 2023; in Canada it has been considered endangered since about 2012.

An interagency monitoring program

Long-term monitoring of whitebark pine as a "vital sign" shows trends in disease, insect infestation and regeneration, and guides management.

• Who. Under the Greater Yellowstone Coordinating Committee, the NPS Inventory and Monitoring Division's Greater Yellowstone Network and other agencies formed the Greater Yellowstone Whitebark Pine Monitoring Working Group — the NPS, U.S. Forest Service, U.S. Geological Survey, Bureau of Land Management and Montana State University. Since 2004 the Greater Yellowstone Network has led monitoring on NPS and Forest Service lands.
• The protocol. The group developed a monitoring protocol from 2004 to 2007; after rigorous peer review, the Interagency Whitebark Pine Monitoring Protocol for the Greater Yellowstone Ecosystem was approved in 2007 and updated in 2011.
• Wyoming BLM lands. Since 2013 the Wyoming BLM has monitored whitebark and limber pine in mapped five-needle pine stands, for a fuller regional picture. Those results are reported in a separate NPS series, not in this one.

The Greater Yellowstone Ecosystem includes three national parks, five national forests and Bureau of Land Management lands. Credit: National Park Service.

What the program asks

Two questions for land managers:

• Is white pine blister rust increasing in the GYE?
• Is the resulting death of whitebark pine enough to justify intervention, such as active protection or restoration?

Four objectives, all for trees taller than 1.4 metres except the last:

Methods and analysis will adapt as conditions and management needs change. Later articles in the series give results for each objective, the methods, and protection and restoration efforts.

Sources

• National Park Service, Greater Yellowstone Inventory and Monitoring Network, "Interagency Whitebark Pine Monitoring Program in the Greater Yellowstone Ecosystem — Overview." https://www.nps.gov/articles/000/interagency-whitebark-pine-monitoring-program-in-the-greater-yellowstone-ecosystem-overview.htm
• The article draws on Tomback and Kendall (2001), Ellison and others (2005), Tomback and others (1993, 1995), Logan and others (2009), Westerling and others (2011), Keane and others (2012), Arno (1986), Ebenman and Jonsson (2005), Shanahan and others (2016, 2022) and the monitoring protocol (Greater Yellowstone Whitebark Pine Monitoring Working Group, 2011).
• Rewritten in hubnx's own words.