Document: TAL-3-42-26

Climatic sensitivity of pinyon pine as a predictor of resistance to insect herbivory: An integration of dendrochronology and a long-term insect removal experiment.

TROTTER III, R.T.*, N.S.COBB and T.G.WHITHAM

Northern Arizona Unversity, Flagstaff AZ U.S.A. ¹

Abstract:
Using dendrochronological data and a 14-year insect removal experiment we examine how the environmental sensitivity of individual trees predicts their susceptibility to chronic attack by the Pinyon Needle Scale (Matsucoccus acalyptus). Several key findings emerge: First, our data indicate that chronic infestation by scales reduces annual ring growth by 37%. Second, long-term removal of the scales results in an increase in ring growth, such that susceptible growth mirrors that of resistant trees. This system is among the first to experimentally demonstrate a 'herbivore signal' in a dendrochronological record. Third, new to this study is the indication that inherently resistant trees demonstrate 68-fold greater inter-annual variation in ring growth during the experimental period, relative to susceptible trees. Removal of the scales from susceptible trees results in 1.6 fold increase in inter-annual ring width variation. While this experimental increase in inter-annual variability during the experimental period indicates some herbivore impact on host climatic sensitivity, the diminutive level of increase following herbivore removal indicates there are inherent differences in climatic sensitivity between resistant and susceptible trees. The differences between resistant an susceptible trees highlight the need to better understand within population variation in environmental sensitivity and host herbivore interactions in the reconstruction of past climate, and suggest a mechanism for predicting relative regional susceptibility to outbreaks.

Keywords: dendrochronology, insect herbivory, long-term experiment, host climate sensitivity, herbivore resistance and susceptibility

This abstract is being presented at: 9:30 AM in session:
Oral Session #44: Terrestrial Invertebrates: Foodwebs and Plant Responses.