Pine butterfly (Neophasia menapia) outbreak in the Malheur National Forest, Blue Mountains, Oregon : examining patterns of defoliation Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kw52jd04h

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  • The pine butterfly (Neophasia menapia C. Felder & R. Felder) (Lepidoptera: Pieridae) is a relatively host-specific defoliator of ponderosa pine (Pinus ponderosa Dougl. ex Laws). From 2008 to 2012, the Malheur National Forest was subject to an outbreak of pine butterfly in ponderosa pine, peaking at ~100,000 ha of forest visibly defoliated in 2011. Silvicultural-based management guidelines have been used to manage stand resilience to other insect defoliators, but guidelines specific to the pine butterfly are currently lacking. The goal of this study is to examine pine butterfly defoliation patterns to relate stand and tree structure characteristics to inform management guidelines. I randomly sampled 25 stands within ponderosa pine forests delineated as heavily defoliated in 2011 by annual forest health aerial surveys. Within each stand I randomly located three transect plots, 10 x 40m, and measured diameter at breast height (DBH), height, and estimated defoliation for the entirety of all trees > 5cm DBH. Data was analyzed using linear mixed effects models to account for all other determinants of defoliation before measuring variables under study. Defoliation averaged 67% for all trees. Stand density index, stand structure, tree crown class, and level within a tree canopy demonstrated no meaningful effects on mean defoliation. I infer from these results that defoliation levels during pine butterfly outbreaks are not influenced by structural or crown characteristics; virtually all available foliage is consumed in these single host-species stands (though note that ~10% of trees studied showed <50% defoliation levels). This suggests that the most relevant factor to managers interested in reducing tree mortality and growth loss may prove to be individual tree health prior to an outbreak. Therefore, standard silvicultural recommendations of thinning ponderosa pine to reduce competition and increase tree vigor and resilience is likely to be a good course in areas that are prone to pine butterfly outbreaks, although the best available information suggests that thinning should not be conducted during an outbreak.
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