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Two pines with needles in bundles of five hold up the high country of the Greater Yellowstone Ecosystem: whitebark pine and limber pine. Both are in trouble, from an imported fungus, beetles, parasites, fire and drought. Since 2013 the Bureau of Land Management has been counting and measuring them on its forests in Wyoming, alongside the Park Service's long-running whitebark pine monitoring. This is how the programme works.
A monitoring plot at Brent Creek, Wyoming. NPS
Two keystone trees
| Whitebark pine | Limber pine | |
|---|---|---|
| Where | subalpine forests | montane and lower woodlands; on rocky, dry ground, often limestone or sandstone |
| Range | high country of the northern Rockies and Greater Yellowstone | from the Canadian Rockies to New Mexico and Arizona, and from southern California east to isolated stands on the edge of the Dakotas and Nebraska |
| Role | a keystone species and a pioneer: it grows where little else can, changes the local climate, and lets trees such as subalpine fir take hold after it | plays a similar part in lower forests |
| Seeds | large, wingless, planted almost entirely by Clark's nutcrackers | the same |
| Who eats them | grizzly bears, red squirrels, nutcrackers and many small seed-eating mammals | — |
| Status | Threatened under the Endangered Species Act since January 17, 2023 | a species of concern on Wyoming BLM land |
Whitebark pine has almost no commercial value, which is part of why its decline went unnoticed for so long.
What is killing them
- White pine blister rust, a fungus (Cronartium ribicola) brought from abroad, has killed whitebark pine across the Pacific Northwest and parts of the northern Rockies over the last century.
- Mountain pine beetle outbreaks between 2000 and 2010 killed vast stands of mature whitebark pine at high elevations.
- Together, rust and beetles have shifted Greater Yellowstone's whitebark pine toward small trees, threatening its ability to reproduce.
- Fire used to help whitebark pine persist; with snowpack melting earlier and faster in a warmer climate, fires are becoming more frequent and more intense.
- Limber pine dwarf mistletoe (Arceuthobium cyanocarpum), a parasitic plant, has killed many limber pines across the Rockies. By the time it can be seen, a tree has usually been infected for five to seven years or more; it stunts growth and damages the crown, and kills small understory trees faster, though big trees can live a century or more with it. Monitoring since 2004 has found it only occasionally on whitebark pine, but recent surveys on Wyoming BLM forests have found it on more limber pines.
The monitoring programme
The Wyoming BLM ran a pilot in 2013 and 2014 on its lands within Greater Yellowstone, and folded the long-term work into the interagency whitebark pine monitoring programme. It follows that programme's protocol, with two differences: it covers limber pine as well as whitebark, and it adds a rapid assessment method designed for stands where five-needle pines are sparse. In a rapid assessment, trees are not tagged and only some measurements are taken, so a crew can run several transects per stand instead of one — a broader picture of each stand's health.
What it measures:
- the share of live pines taller than 4 metres infected with blister rust;
- how severe the rust is — where on each tree, and which infections persist and which are new;
- how many trees die, and what is likely killing them;
- whether young pines in the understory are making it into the cone-bearing population.
Where
Eight areas of Wyoming BLM land were chosen after ground surveys confirmed five-needle pines grow there:
| Brent Creek | Teton Valley Ranch Camp |
| Rattlesnake | Clark's Fork Canyon |
| Pine Grove / Deadline Ridge | Commissary Ridge |
| Scab Creek | Sublette Range / Huff Creek |
The Wyoming BLM study sites, with the region's Park Service and Forest Service whitebark pine monitoring sites. NPS
This is the first article in a Park Service series on the programme; the next summarises what the 2023 monitoring found about blister rust, deaths and young trees.
Sources
Written from "Five-Needle Pine Monitoring Program on Wyoming Bureau of Land Management Forests in the Greater Yellowstone Ecosystem — Overview," National Park Service, Greater Yellowstone Network; a work of the United States government in the public domain. It draws on the interagency monitoring protocol (Greater Yellowstone Whitebark Pine Monitoring Working Group, 2011), Shanahan and others (2016, 2022), Tomback and others (1993, 2001), Logan and others (2009) and Westerling and others (2011).
Licens: CC0 1.0 (allmän egendom) · Bearbetat efter www.nps.gov
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