Identifying and Separating Pandora Moth Outbreaks and Climate from A 1500-Year Ponderosa Pine Chronology from Central Oregon

Abstract

We reconstruct pandora moth (Coloradia pandora Blake) outbreaks and climate from a 1572-year (435-2006 CE) ponderosa pine (Pinus ponderosa Dougl. ex Laws.) chronology from a lava flow in central Oregon. We took samples from 128 living trees and remnant logs and crossdated the samples using skeleton plots and COFECHA for quality control. After cutting out and removing those time periods from the chronology during which insects become the main limiting factor to growth, we examine the response of tree rings to climate. Evidence of species longevity (up to 877 years), presence of periodic pandora moth defoliations (13 total), and a significant relationship with the Palmer Drought Severity Index were observed (R2 = 0.34, p < 0.001). Suppressions related to pandora moth outbreaks were recorded back to 618 CE, with a mean return interval of 104 years. Previous-fall to current-spring PDSI was reconstructed over 1376 years (630-2006 CE), where the most prolonged drought periods were 1136-1166 CE and the Dust Bowl 1924-1941. Our research documents longevity of ponderosa pine, resilience in the presence of multiple disturbances, and demonstrates a technique to separate insect outbreak signals from climate reconstructions in long chronologies while embracing the entire signal available in tree rings. © 2017 by The Tree-Ring Society.