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Vulnerability of Great Basin bristlecone pine to mountain pine beetle

Status: 
Action
Dates: 
May, 2014

Bristlecone pine mortality.
Bristlecone pine mortality.
Great Basin bristlecone pine (GBBP) (Pinus longaeva) is a long-lived species found at high elevations in Utah, Nevada, and southeastern California (CA). 'Methuselah', a GBBP found in the White Mountains, CA, is the oldest known living non-clonal organism. Foxtail pine (FTP) (P. balfouriana) is a rare pine endemic to high elevations in southern and northern CA. GBBP and FTP are sister species, likely evolved from an extinct species that diverged from Rocky Mountain bristlecone pine (P. aristata). Both GBBP and FP can be found growing in stands with other pines, including limber pine (LMP) (P. flexilis), that are known hosts to mountain pine beetle (MPB) (Dendroctonus ponderosae). MPB occurs within the ranges of GBBP and FTP but it is uncertain if these species are suitable hosts.

Terpenoids are key components of pine defense against MPB, and resin stored in constitutive ducts act as both a physical and chemical deterrent to attacking beetles. Characteristics of wood including resin ducts, density and tracheids have also been associated with resistance against bark beetle attack. Trees with smaller and fewer resin ducts were more likely to be successfully attacked by MPB.

Our goal is to evaluate vulnerability of GBBP and FTP to MPB attack, and to identify where tree mortality is occurring to inform efforts for protection and genetic conservation of these keystone species.  We are also examining chemical and morphological defense characteristics of each species to better understand traits that may confer resistance to MPB attack.

Coring a bristlecone pine to determine its age.
Coring a bristlecone pine to determine its age.
Bristlecone pine grow at high elevations.
Bristlecone pine grow at high elevations.

Approach

We identified sites with co-occurring GBBP-LMP and FTP-LMP where MPB activity was also noted in Aerial Detection Surveys. Across nine areas, we surveyed 266 fixed-radius plots and recorded tree DBH and MPB-attacks. Between plots, we conducted 100% surveys along ~3 chain-wide transects, and all GBBP, FTP and LMP attacked by MPB were recorded. At six areas 15 trees of each species (GBBP or FTP and LMP) were sampled. Two cores were removed from each tree and will be used to determine age, wood density, and resin duct characteristics. A phloem sample was also removed from each tree for terpene analyses. We extracted monoterpenes from samples and measured terpene quantity and composition using gas chromatography.

Key Findings

  • Preliminary results suggest that GBBP are not attacked by MPB. Despite MPB attacks on LMP growing in the same stands, GBBP were not attacked by MPB, although a small percentage of FTP were attacked and killed by MPB.
  • Total monoterpenes, a trait associated with greater defense, was higher in GBBP and FTP than LMP.
  • Tree cores and phloem terpene samples are currently being analyzed to evaluate additional defense differences among tree species that could explain resistance/susceptibility to MPB.
  • Common garden lab experiments will evaluate the suitability of GBBP, LMP, and FTP for MPB reproduction and fitness.


Project Contact: 

Principal Investigators:
Co-Investigators:
Sharon Hood - University of Montana

Collaborators:
Sheri Smith - USDA Forest Health Protection
Darren Blackford - USDA Forest Health Protection

Research Staff: