WWETAC Projects

Project Title:  Synthesis of dendrochronology methods used to detect insect outbreaks

Principal Investigator:   Ann M. Lynch, US Forest Service, Rocky Mountain Research Station, Forest & Woodlands Ecosystems Program, Tucson, AZ


Collaborators:   René I. Alfaro, Canadian Forest Service, Pacific Forestry Centre; Christopher D. O’Connor, Univ. Arizona, Sch. Natural Resources & the Environment (PhD Candidate); Thomas W. Swetnam, University of Arizona, Laboratory of Tree-Ring Research

Key Issues/Problem Addressed:              
Many researchers who use tree-ring analysis to reconstruct insect outbreaks have little background in insect ecology and population dynamics and therefore fail to incorporate consideration of important factors in their investigations and interpretations, or apply inappropriate statistical procedures. There is a need for synthesis publications that review the state of knowledge for dendroentomology that incorporates both dendrochronology methodology and insect ecology information so that a) dendrochronologists initiating work to reconstruct insect outbreak chronologies have a better understanding of essential insect ecology factors and can avoid common mistakes, and b) entomologists, other ecologists, and professionals have a better understanding of the dendrochronology procedures and limitations.

There is also a need to establish a research framework for developing dendroentomology procedures that more precisely date the onset of forest insect outbreaks. Precise dating of outbreak initiation is critical to determining what factors are directly related to outbreak initiation.

Setting and Approach:  

There have been substantial advances in the 27 years since Swetnam et al. (1985) published the nonhost procedure that underlies most dendroentomology work today.  Lynch (2012) reviewed much of what has been learned about coniferous defoliator outbreaks from dendroentomology, but not the procedures involved, information pertaining to bark beetles, or the significant number of issues that need to be addressed when conducting and interpreting dendroentomology investigations.

Progress to Date:

Compilation of the entomology-related literature is complete.  Manuscript sections that are in draft condition include a review of insect ecology concepts that should be considered in tree-ring studies, dendrochronology issues that should be considered by entomologists interpreting tree-ring reconstructions, and the methods used to recognize and reconstruct defoliator and bark beetle outbreak regimes.  Work that remains includes bringing these sections to final form, adding depth to the bark beetle section, a comparison of how dendrochronology performs for reconstructing different types of outbreaks (eruptive vs gradual outbreak development, short vs long duration outbreaks, defoliators vs bark beetles), and reviewing the potential utility of recent developments in dendrochronology.


Methodology for detecting insect outbreak in tree-ring chronologies will be available in a synthesis format that permits researchers to more easily determine what methods are best suited to their situation and to understand how various insect ecology factors need to be considered.  Science-users will have ready access to information in a comprehensive format that enables them to understand the complex methodology involved, its strengths, and weak.  The “state of knowledge” regarding dendrochronology (not limited to dendroentomology) will be reviewed in order to assess potential for new methods to detect the initial stages of insect outbreaks in tree-ring series.

WWETAC ID:      FY12NG110

Lynch A.M.  2012.  Long term records: What dendrochronology tells us about coniferous defoliators.  Pp. 126-154 in Barbosa P., Letorneau D.K., and Agrawal A. (editors), Insect Outbreaks Revisited.  Wiley-Blackwell.  465 p.

Swetnam T.W., Thompson M.A., and Sutherland E.K.  1985.  Using dendrochronology to measure radial growth of defoliated trees.  USDA For. Serv., Coop. St.Res. Serv., Agric. Handb. 639, 39 p.