How Whitebark Pine Is Monitored in Greater Yellowstone: The Interagency Methods

About this article

This is the fifth article in a Park Service series on whitebark pine (Pinus albicaulis) monitoring in the Greater Yellowstone Ecosystem (GYE). It summarizes how Greater Yellowstone Inventory and Monitoring Network crews track the trees' health. Full details are in the Interagency Whitebark Pine Monitoring Protocol, Version 1.1 (2011).

The study area

The GYE is the Yellowstone Plateau volcanic fields and the 14 mountain ranges around them: three national parks — Yellowstone, Grand Teton and the John D. Rockefeller, Jr. Memorial Parkway, which Grand Teton administers — five national forests (Beaverhead-Deerlodge, Bridger-Teton, Custer Gallatin, Shoshone and Caribou-Targhee) and Bureau of Land Management (BLM) land.

The Greater Yellowstone Ecosystem's parks, forests and BLM land. NPS.

What's sampled

Whitebark pine grows, alone or mixed, on more than 2.5 million of the GYE's 15 million+ acres. The program covers all whitebark pines on Park Service and Forest Service land.

• Stands: contiguous forest where whitebark pine is dominant or codominant, about 2 hectares (5 acres) or larger, inside and outside the U.S. Fish and Wildlife Service's grizzly bear recovery zone. When monitoring began in 2004, mapping found 10,770 stands — 2,362 inside the zone and 8,408 outside. Areas burned after 1970 were left out.
• BLM: five-needle pine stands on Wyoming BLM land have been sampled since 2013, and Montana BLM began its own program in 2022 with the same protocol; those data are reported in a separate series.

The design

A two-stage cluster design: whitebark pine stands are the first stage, and 10 × 50 m transects within them the second, a probabilistic sample that supports conclusions about the whole GYE population.

• 2004–2007: crews set up 176 permanent transects in 150 stands and put aluminum tags on every live whitebark pine taller than 1.4 m — 4,768 trees — recording each tree's diameter and any blister rust.
• Panels: after 2007, stands were randomly split into four rotating panels of about 44 transects — as many as a two-person crew can survey in a season, from late June to mid-September. Each panel is revisited every four years, about the time it takes blister rust to show visible signs after infection.

Whitebark pine survey transects across the ecosystem. NPS.

The panel revisit schedule, including mortality-only surveys during the mountain pine beetle epidemic. NPS.

Reading the results: the program's deeper evaluations come every four years, after all 176 transects have been resurveyed. Each year's panel is a different set of transects, so comparing single years is misleading, and one year's data don't represent the whole population's status or trend.

The four objectives

1. Infection: the share of trees over 1.4 m with white pine blister rust, and how it changes.
2. Severity: how serious infections are, and how that changes.
3. Survival: tree survival, accounting for blister rust, mountain pine beetle and wildfire.
4. Recruitment: how young whitebark pines join the reproducing population, and what affects it.

1. Is the tree infected?

Every live tree on the transect is checked. A tree counts as infected if it has aecia (spore blisters) or cankers — and a canker counts only if at least three of five signs are present: flagging (clusters of brown needles), rodent chewing, oozing sap, roughened bark and swelling.

Signs of blister rust cankers: flagging, swelling, roughened bark (top); chewing and oozing sap (bottom). NPS / Shanahan; swelling, USFS / Hoff.

Checking a whitebark pine for blister rust; brown "flagging" suggests infection. NPS.

Animals and insects chew through bark to reach the sweet spores; the tree oozes sap to seal the wound. NPS / Shanahan.

2. How severe?

Crews record whether a canker is in the canopy (branches) or on the bole (trunk) — a canker on a branch within 5 cm of the trunk counts as bole. Bole cankers are worse: they block nutrients to everything above and, low on the trunk, eventually kill the tree, though it may survive for decades. On later visits, crews see whether canopy infections have spread to the trunk — or disappeared, since trees self-prune branches, rodents eat cankers, and resistant trees can wall off infections that scar over.

A caution: a 2017 analysis found only moderate to low agreement between observers on canker location, though high agreement on whether a tree is infected at all. In 2020, one observer with more than 20 years' experience surveyed all 30 transects — but some subjectivity always remains.

3. Is the tree alive?

A tree with any green needles is alive. Crews note what may be harming it: mountain pine beetle, blister rust, animals, or mechanical damage such as windthrow, fire scars and needle cast.

• Beetle signs on live trees: pitch tubes — popcorn-shaped resin blobs a tree pushes out to fend off beetles — and frass, the boring sawdust in bark crevices and at the base.
• Dead trees: crews peel back bark looking for J-shaped galleries, proof that beetles and their larvae lived there.
• The epidemic: during the 2008–2013 beetle outbreak, every transect was surveyed every two years to track deaths, before returning to the four-year cycle.

A J-shaped gallery where mountain pine beetles laid eggs. NPS.

A beetle caught in a pitch tube. NPS / Shanahan.

4. Are new trees coming up?

A newly emerged five-needle pine seedling. NPS / Shanahan.

Because limber pine (Pinus flexilis) looks the same as whitebark without cones, some counts are for "five-needle pines." On each transect crews count:

• understory five-needle pines under 1.4 m (average density = total counted ÷ transects visited);
• whitebark pines that grow past 1.4 m, which are then tagged;
• tagged trees showing cones or cone scars, binned as 0, 1–5, 6–10 or more than 10 cones, or S for scars only.

Three circular 1/300-acre subplots (2.08 m radius), at the start, middle and end of each transect, record five-needle pines in four height classes; other trees — lodgepole pine, fir, spruce, aspen — in two; bare ground and plant cover (by Daubenmire cover classes); dominant plants; and blister rust. Subplots are done only when the whole transect is free of snow. Young pines 61.1–140 cm tall get a special recruitment tag so they can be followed into the main sample.

The three recruitment subplots within a transect. NPS.

Data

All data pass rigorous quality checks; small corrections to the master database can shift past figures slightly (typically under 1%). Analyses use Excel and R. Data for every year are on the Park Service's IRMA portal.

Sources

Based on "Methods for the Interagency Whitebark Pine Monitoring Program in the Greater Yellowstone Ecosystem," Greater Yellowstone Inventory and Monitoring Network, National Park Service; a work of the United States government in the public domain.