Predictors of Ips confusus Outbreaks During a Record Drought in Southwestern USA: Implications for Monitoring and Management |
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Authors: | Maria J Santos Thomas G Whitham |
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Institution: | (1) Center for Environmental Sciences and Education, Northern Arizona University, PO Box 5694, Flagstaff, AZ 86001-5694, USA;(2) Department of Land, Air and Water Resources, University of California, One Shields Avenue, Davis, CA 95616-8585, USA;(3) Department of Biological Sciences and Merriam-Powell Center for Environmental Research, Northern Arizona University, PO Box 5640, Flagstaff, AZ 86011, USA |
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Abstract: | In many ecosystems the effects of disturbance can be cryptic and disturbance may vary in subtle spatiotemporal ways. For instance,
we know that bark beetle outbreaks are more frequent in temperate forests during droughts; however, we have little idea about
why they occur in some locations and not others. Understanding biotic and abiotic factors promoting bark beetle outbreaks
can be critical to predicting and responding to pest outbreaks. Here we address the environmental factors which are associated
with Ips confusus outbreaks during the 2002 widespread drought within the distribution range of pinyon pine woodlands in Arizona. We used univariate
statistics to test if whether tree characteristics, other herbivores, stand properties, soil type, wind, and topography were
associated with I. confusus outbreak, and logistic regression to create a predictive model for the outbreaks. We found that I. confusus attacks occur in low elevation stands on steeper slopes, where favorable winds for I. confusus dispersion occur. I. confusus select larger trees, in high density stands with understory shrubs that exhibit phenotypic traits characteristic of resistance
to stem-boring moths. The model was highly accurate, and explained 95% of the variability in occurrence (98% of the absences
and 95% of the presences). Accurate prediction of the impacts of disturbance allow us to anticipate, minimize or mitigate
for and eventually counteract its effects, especially those affecting diversity and ecosystem function. Identification of
outbreak risk areas can guide regional and national management towards the reduction of infestation risk and enhancing conservation
of pinyon-juniper woodlands. |
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