You are here

Traumatic resin ducts indicate past beetle outbreaks

Date: September 20, 2017

The presence of traumatic resin ducts, defined as resin ducts aligned tangentially and arranged compactly, indicated mechanical damage associated with epidemic spruce beetle populations.


Background

The formation of traumatic resin ducts in Engelmann spruce represents an important induced defense in response to environmental perturbations. The occurrence and strength of resin ducts, in particular traumatic resin ducts, in annually resolved tree rings could be used to reconstruct a tree’s structural damage in association with natural disturbances. In this study, we focused on the potential to reconstruct past spruce beetle outbreaks.

Research

Crossdating and digitizing an increment core using a microscope and sliding stage. Photo by Lawrence Lam.
Crossdating and digitizing an increment core using a microscope and sliding stage. Photo by Lawrence Lam.
We analyzed tree-ring data from paired live and dead Engelmann spruce from the severe spruce beetle outbreak on the Markagunt Plateau in southwestern Utah. The data was collected from increment cores, which were sanded and crossdated using the marker year approach and digitized using a microscope and a sliding stage. We found that the traumatic resin duct prevalence during the outbreak was significantly higher than over tree lifespans. All other metrics characterizing tree vigor, (diameter, age, ring width, and basal area increment), were not significantly different between live and dead trees.

We found that 90 percent of the live Engelmann Spruce exhibited traumatic resin ducts during a calendar year in close proximity to (1-3 years prior to or after) the date of death indicated by its paired dead tree that succumbed to mass attack during the spruce beetle outbreak. Forty percent of the dead trees exhibited traumatic resin ducts 1-3 years prior to their date of death. The prevalence of traumatic resin ducts over the lifetime of an Engelmann Spruce was exceedingly rare. Regardless of a tree’s live or dead status, half (49 percent) of all traumatic resin ducts occurred during the two decades of the spruce beetle outbreak.

Findings

  • The inherent capability to produce traumatic resin ducts that can ‘pitch out’ attacking spruce beetles could be the primary mechanism by which Engelmann spruce survived the outbreak over the past two decades (1990s and 2000s).

  • Because traumatic resin duct production in our sampled Engelmann spruce was exceedingly rare, this discovery represents a new line of tree-ring-based evidence that can be used to reconstruct other spruce beetle outbreaks.



Principal Investigators: 
Principal Investigators - External: 
Matthew Bekker - Brigham Young University
James N. Long - Utah State University
Research Location: 
Utah