What tree-ring reconstruction tells us about conifer defoliator outbreaks

Abstract

Our ability to understand the dynamics of forest insect outbreaks is limited by the lack of long-term data describing the temporal and spatial trends of outbreaks, the size and long life span of host plants, and the impracticability of manipulative experiments at relevant temporal and spatial scales. Population responses can be studied across varying site and stand conditions, or for a few years under somewhat controlled circumstances, but it is difficult to study temporal variability for species that outbreak only two or three times a century. Fortunately, dendrochronology enables us to explore decadal- and century-scale outbreak dynamics at spatial scales ranging from within-tree to continental. Evidence of past insect defoliation can be identified, dated, and sometimes quantified using variation in the width and morphology of annual growth rings in trees (Plate 7.1). Mortality events can be identified and dated by dating the last growth ring on dead trees, growth release events in survivors, and postdisturbance recruitment events. Insect defoliation can be distinguished from weather and other disturbance agents by comparing responses in host and nonhost trees.

Citation

Lynch, Ann M. 2012. What tree-ring reconstruction tells us about conifer defoliator outbreaks. In: Barbosa, Pedro; Letourneau, Deborah K.; Agrawal, Anurag A., eds. Insect Outbreaks Revisited. Hoboken, NJ: Blackwell Publishing Ltd. p. 126-154.