How Scientists Monitor Whitebark and Limber Pines on Wyoming’s BLM Lands

Whitebark pine (Pinus albicaulis) and limber pine (Pinus flexilis) — the “five-needle pines” — grow on Bureau of Land Management (BLM) forests in Wyoming, part of the Greater Yellowstone Ecosystem. Monitoring there tracks three things: infection by white pine blister rust, tree deaths, and recruitment — young trees coming up to replace the old. This article, the last in an NPS series, explains how.

Collecting data at a tagged whitebark pine. NPS/Shanahan.

Two kinds of survey

The work follows the Interagency Whitebark Pine Monitoring Protocol for the Greater Yellowstone Ecosystem, which surveys permanent belt transects, 10 by 50 meters, with tagged trees. That protocol targets dense whitebark pine stands — but on Wyoming BLM land the pines are often sparse. So crews add a second method designed for this effort: rapid assessment transects, which allow many more samples and a more accurate picture of rust infection and overall health.

Choosing where to look

Both surveys use a stratified two-stage cluster sample:

1. Each geographic area identified by BLM is a stratum — such as Commissary Ridge, Brent Creek, Teton Valley Ranch, Rattlesnake, Clark’s Fork Canyon, Pine Grove/Deadline Ridge, Scab Creek and Sublette Range/Huff Creek.
2. Within each, map units of at least 2.5 hectares are the first-stage samples.
3. Within a map unit, points for 10 × 50 m transects are chosen with the Generalized Random Tessellation Stratified (GRTS) design, a spatially balanced random method that spreads samples across the whole area.

Example stratum (Commissary Ridge) with three map units and ten random points in each. NPS.

Permanent transects: eight were set up in 2013 and 2014, with 146 live trees taller than 1.4 m tagged. They form four panels of two, each revisited every four years alongside the interagency whitebark pine transects.

Rapid transects: for each map unit, GRTS picks 10 random points in random order. Crews navigate by GPS to each in turn. A point qualifies only if it has at least one live five-needle pine taller than 1.4 m; if not, they move to the next. Surveying stops at five qualifying transects or when all 10 points are used. Since nothing is marked, a fresh set of 10 points is drawn for every revisit.

What crews record

Measuring white pine blister rust (Cronartium ribicola) cankers. NPS/Shanahan.

• Blister rust: every live tree is checked; a tree counts as infected if it has aecia or cankers. To gauge severity, crews note whether cankers are in the canopy (branches) or on the bole (trunk).
• Death: every tree taller than 1.4 m is recorded as alive or dead. On live trees crews note blister rust, dwarf mistletoe, mountain pine beetle attack (pitch tubes, frass), fire, or other damage such as windfall or avalanche; on dead trees, the J-shaped galleries beetles leave under the bark.
• Recruitment: three counts per transect — trees 1.4 m or shorter, trees taller than 1.4 m, and live tagged trees showing reproductive activity — plus cone production. On permanent transects only, three small circular 1/300-acre subplots also record other understory trees and ground cover.

An emergent five-needle pine seedling. NPS/Shanahan.

Sources

Based on "Methods for Five-Needle Pine Monitoring on Wyoming Bureau of Land Management Forests in the Greater Yellowstone Ecosystem," National Park Service, drawing on the interagency monitoring protocol (2011) and Shanahan et al. (2022); a work of the United States government in the public domain.