Five-Needle Pine Monitoring Program on Wyoming Bureau of Land Management Forests in the Greater Yellowstone Ecosystem—Overview

Five-needle pine monitoring plot at Brent Creek, Wyoming.

NPS

This article begins the article series, “Five-Needle Pine Monitoring on Wyoming Bureau of Land Management Forests in the Greater Yellowstone Ecosystem.”

The Greater Yellowstone Ecosystem is home to 2 five-needle pine species, both of which play important ecological roles: whitebark pine (Pinus albicaulis) and limber pine (Pinus flexilis).

Whitebark pine is a keystone species of subalpine forests, regulating many ecological processes and influencing biodiversity (Tomback and Kendall 2001; Ellison et al. 2005). Whitebark pine is considered a “pioneer” species due to its tolerance of harsh environmental conditions and ability to establish and persist where other species cannot. In doing so, whitebark pine can alter the microclimate and enable species such as subalpine fir (Abies lasiocarpa) to establish in these otherwise inhospitable regions (Tomback et al. 1993). Although whitebark pine has very little commercial value, its seeds provide seasonal forage for a variety of wildlife, including grizzly bears (Ursus arctos horribilis), red squirrels (Tamiasciurus hudsonicus), Clark’s nutcrackers (Nucifraga columbiana), and a variety of granivorous small mammals.

Limber pine occurs in western North America across a broad elevational gradient from the Canadian Rocky Mountains into parts of New Mexico and Arizona and from southern California eastward to the few, isolated populations existing on the western boundary of the Dakotas and Nebraska (Steele 1990; Schoettle and Rochelle 2000). A relatively adaptable five-needle pine, it is typically encountered on rocky, xeric sites with limestone or sandstone soils (Steele 1990). In Wyoming, limber pine is an important species in montane and lower woodland ecosystems, where it provides ecosystem functions similar to those of whitebark pine (Thompson et al. 1976; Steele 1990; Kearns and Jacobi 2007). Like whitebark pine, limber pine depend principally on Clark’s nutcrackers (Nucifraga columbiana) to disseminate their wingless seeds (Lanner and Vander Wall 1980).

Current Threats to Five-Needle Pines

Multiple ecological disturbances currently impact whitebark pine and limber pine. White pine blister rust (hereafter, blister rust) caused by the introduced fungus Cronartium ribicola, mountain pine beetle (Dendroctonus ponderosae), dwarf mistletoe (Arceuthobium spp.), wildfires, and drought all pose significant threats to the persistence of healthy five-needle populations.

In the last century, blister rust has caused significant whitebark pine mortality in the Pacific Northwest and parts of the northern Rockies (Arno 1986). Between 2000 and 2010 widespread infestations of mountain pine beetle in high elevation stands have killed expansive swaths of mature whitebark pine forest (Logan et al. 2009). In the Greater Yellowstone Ecosystem (GYE) the combination of blister rust damage and mortality from mountain pine beetles has shifted whitebark pine populations to smaller sized trees and threatened whitebark pine reproduction and overall survival (Shanahan et al. 2016). Furthermore, fire regimes, which have historically been important for whitebark pine persistence, are becoming more frequent and increasing in intensity as snowpack melts earlier and faster due to rising temperatures (Westerling et al. 2011). These combined threats led the US Fish and Wildlife Service to list the whitebark pine as Threatened under the Endangered Species Act on January 17, 2023.

Limber pine dwarf mistletoe (Arceuthobium cyanocarpum).

Colorado State Forest Service/Bill Ciesla

Limber pine dwarf mistletoe (Arceuthobium cyanocarpum; dwarf mistletoe) poses health impacts somewhat unique to limber pine. Dwarf mistletoe has caused extensive mortality in limber pine populations throughout areas of the Rocky Mountains (Mathiasen and Hawksworth 1988). Once indicators of dwarf mistletoe are visually apparent, it is generally assumed that infection is present at an advanced stage (5 to 7 years plus). Tree vigor is greatly compromised by mistletoe infection, as evidenced by a reduction in tree growth and damage to the upper canopy of an infected tree. While mistletoe can cause more rapid mortality in smaller, understory trees, larger, mature trees can live for 100+ years with mistletoe infections (Geils et al. 2002). Since the initiation of whitebark pine monitoring in the Greater Yellowstone Ecosystem (GYE) in 2004, occasional dwarf mistletoe infections have been noted in a small number of whitebark pine trees in the GYE. Recent work on Wyoming Bureau of Land Management (BLM) forests, however, has documented an increase in dwarf mistletoe presence in some populations of surveyed limber pine.

Monitoring Program

Whitebark pine is a Threatened species under the Endangered Species Act and limber pine is a species of concern on Wyoming BLM lands. To understand the many challenges faced by five-needle pines and to track their health status, the Wyoming BLM initiated a pilot monitoring program on Wyoming BLM lands where five-needle pine species occur within the GYE. Based on data collected in 2013 and 2014, a five-needle pine long-term monitoring effort on Wyoming BLM lands was assimilated into the interagency whitebark pine monitoring program. While similar to the Interagency Whitebark Pine Monitoring Protocol for the Greater Yellowstone Ecosystem (GYWPMWG 2011) (hereafter, the monitoring protocol), Wyoming BLM monitoring objectives include both whitebark pine and limber pine and additional data are collected using a rapid assessment sampling methodology specifically designed for this endeavor (Shanahan et al. 2022).

The rapid assessment sampling method was developed in 2013–2014 to augment five-needle pine surveys on Wyoming BLM lands where five-needle pine densities were expected to be lower in some areas compared to other locations sampled within the GYE. The main difference in the rapid assessment method is that trees are not tagged and only a subset of individual tree measurements are recorded. This method enables field crews to survey more transects per delineated stand (compared to one transect per stand following the monitoring protocol), thus gaining a more comprehensive understanding of overall five-needle pine health from several locations throughout a stand.

Measurable Objectives

Measurable objectives of the Wyoming BLM five-needle pine monitoring program:

1. Estimate the proportion of live, five-needle pine trees (>4 m tall) infected with white pine blister rust.

2. Document blister rust infection severity by the occurrence and location of persisting and new infections.

3. Determine mortality of five-needle pine trees and describe potential factors contributing to the death of trees.

4. Assess the multiple components of the recruitment of understory five-needle pine into the reproductive population.

These objectives are similar to the objectives of the GYE interagency whitebark pine monitoring program (GYWPMWG 2011) but include both whitebark pine and limber pine.

Study Area

The five-needle pine study area encompasses portions of BLM lands in Wyoming within the GYE. These Wyoming BLM areas were identified as habitat for five-needle pines and ground-surveyed by Wyoming BLM personnel prior to initiation of the sampling effort (Figure 1).

Eight geographic strata were selected for surveying, including Brent Creek (Brent), Teton Valley Ranch Camp (TVRC), Rattlesnake (Rattle), Clark’s Fork Canyon (CFC), Pine Grove/Deadline Ridge (PGDR), Commissary Ridge (CR), Scab Creek (Scab), and Sublette Range/Huff Creek (SRHC) (Figure 1).

NPS

Figure 1. Map of Wyoming Bureau of Land Management (BLM) five-needle pine study sites. Map also shows additional National Park Service (NPS) and US Forest Service (USFS) whitebark pine monitoring sites in the region. Site abbreviations are: Brent Creek (Brent), Teton Valley Ranch Camp (TVRC), Rattlesnake (Rattle), Clark’s Fork Canyon (CFC), Pine Grove/Deadline Ridge (PGDR), Commissary Ridge (CR), Scab Creek (Scab), and Sublette Range/Huff Creek (SRHC).

References

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Ellison, A. M., M. S. Bank, B. D. Clinton, E. A. Colburn, K. Elliot, C. R. Ford, et al. 2005. Loss of foundation species: consequences for the structure and dynamics of forested ecosystems. Frontiers in Ecology and the Environment 39:479-486.

Geils, Brian W.; Cibrian-Tovar, Jose; Moody, Benjamin. 2002. Mistletoes of North American conifers. Gen. Tech. Rep. RMRS-GTR-98. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Greater Yellowstone Whitebark Pine Monitoring Working Group (GYWPMWG). 2011. Interagency whitebark pine monitoring protocol for the Greater Yellowstone Ecosystem, Version 1.1. Greater Yellowstone Coordinating Committee, Bozeman, Montana.

Kearns, H. S., and W. R. Jacobi. 2007. The distribution and incidence of white pine blister rust in central and southeastern Wyoming and northern Colorado. Canadian Journal of Forestry Research 37:462–472.

Lanner, R. M., and S. B. Vander Wall. 1980. Dispersal of limber pine seed by Clark’s nutcracker. Journal of Forestry 78:637–639.

Logan, J. A., W. W. Macfarlane, and L. Willcox. 2009. Effective monitoring as a basis for adaptive management: a case history of mountain pine beetle in Greater Yellowstone Ecosystem whitebark pine. iForest 2:19–22 [online: 2009-01-21]. http://www.sisef.it/iforest/show.php?id=477

Mathiasen, R. L., and F. G. Hawksworth. 1988. Dwarf mistletoes on western white pine and whitebark pine in northern California and southern Oregon. Forest Science 34:429–440.

Schoettle, A. W., and S. G. Rochelle. 2000. Morphological variation of Pinus flexilis (Pinaceae), a bird dispersed pine, across a range of elevations. American Journal of Botany 87:1797–1806.

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Tomback, D. F., and K. Kendall. 2001. Biodiversity losses: a downward spiral. Ch 12, pages 243-262 in D. F. Tomback, S. F. Arno, and R. E. Keane, editors. Whitebark pine communities: ecology and restoration. Island Press, Washington, DC.

Tomback, D. F., S. K. Sund, and L. A. Hoffman. 1993. Post-fire regeneration of Pinus albicaulis: height-age relationships, age structure, and microsite characteristics. Canadian Journal of Forestry Research 23:113-119.

Westerling, A. L., M. G. Turner, E. A. H. Smithwick, W. H. Romme, and M. G. Ryan. 2011. Continued warming could transform Greater Yellowstone fire regime by mid-21st century. Proceedings of the National Academy of Science of the United States of America 108(32):3165–13170. Published online 2011 July 25. doi: 10.1073/pnas.1110199108 PMCID: PMC3156206.