Whitebark Pine Recruitment in Greater Yellowstone: 2023 Monitoring Results

Five-needle pine seedlings. Without cones, whitebark pine can't be told from limber pine in Greater Yellowstone. NPS / Shanahan.

About these results

This is the fourth article in a Park Service series on whitebark pine monitoring in the Greater Yellowstone Ecosystem. It covers Panel 4 — 44 transects surveyed from June to September 2023, their fourth full revisit — and the protocol's fourth objective: to document how whitebark pine (Pinus albicaulis) is recruited into the reproducing population, and what affects that over time.

Trees are dying on all 176 transects in the ecosystem, yet nearly every one shows new trees coming in. Recruitment is measured three ways on each 10 × 50 m transect:

• understory trees 1.4 m tall or shorter;
• trees that grow past 1.4 m;
• tagged trees of any height showing reproduction.

Three circular 1/300-acre subplots (2.08 m radius) along each transect record other young trees and ground cover. Because young whitebark and limber pine (Pinus flexilis) look alike, some counts cover "five-needle pines" in general. One year's transects are not the whole sample, so these figures shouldn't be used to judge the population's overall status or trends. Details: the methods article and the monitoring protocol.

Whitebark pine's stout, sappy, purplish-brown cones. NPS / Erin Shanahan.

Regeneration and growth

• Understory: 2,575 five-needle pines 1.4 m or shorter on 43 transects (snow covered part of one) — about 60 per transect. Thirty-one (1%) had blister rust.
• New trees: 89 trees newly passed 1.4 m and were tagged, on 23 transects; five (6%) showed blister rust.

Cones

106 tagged trees showed reproduction — this year's cones or last year's cone scars.

• Most cone-bearing trees (95) were over 10 cm in diameter.
• The most common count was 1–5 cones, on 55 trees (52%); 27 (25%) showed only scars, which still mark a tree able to produce cones. Whitebark pine tends to have one big cone year followed by a few lean ones.
• Blister rust can cut cone production by blocking nutrients to and from the canopy, where cones grow. 48 (45%) of the reproducing trees were infected — 29 (60%) in the canopy and 19 (40%) on the bole.

Reproducing whitebark pines by number of cones and diameter, Panel 4, 2023. NPS.

Recruitment subplots

Tagging a young five-needle pine in a recruitment plot. NPS / Shanahan.

Crews completed 132 subplots, counting five-needle pines in four height classes and other trees — lodgepole pine, fir, spruce, sometimes aspen — in two, checking every five-needle pine for rust, and recording ground and plant cover. These data are still under review and will appear in future reports.

More: the 2023 resource brief, past results on the Greater Yellowstone Network site, and the series' previous article, on whitebark pine mortality in 2023.

Sources

Based on "Whitebark Pine Recruitment in the Greater Yellowstone Ecosystem – Data Summary of Monitoring in 2023," Greater Yellowstone Inventory and Monitoring Network, National Park Service; a work of the United States government in the public domain.