The effects of mechanical fuel reduction treatments on the activity of bark beetles (Coleoptera: Scolytidae) infesting ponderosa pineIntroductionMaterials and methodsSite descriptions and treatment prescriptionsApache-Sitgreaves National ForestKaibab National ForestTahoe National ForestExperimental design and analysesBark beetle flight periodicityAnalysis of volatile monoterpenes from chipped and lopped-and-piled slashResultsPost-treatment stand structure and compositionIps species and D. valens flight periodicityResponse by bark beetlesBark beetle-caused tree mortalityVolatile monoterpenes from chipped and lopped tree biomassDiscussionAcknowledgementsReferencesThe effects of mechanical fuel reduction treatments on the activity ofbark beetles (Coleoptera: Scolytidae) infesting ponderosa pineChristopher J. Fettiga,*, Joel D. McMillinb, John A. Anholdb, Shakeeb M. Hamuda,Robert R. Borysa, Christopher P. Dabneya, Steven J. SeyboldaaPacific Southwest Research Station, USDA Forest Service, Davis, CA 95616, USAbForest Health Protection, USDA Forest Service, Flagstaff, AZ 86001, USAReceived 14 September 2005; received in revised form 11 April 2006; accepted 13 April 2006AbstractSelective logging, fire suppression, forest succession and climatic changes have resulted in high fire hazards over large areas of the westernUSA. Federal and state hazardous fuel reduction programs have increased accordingly to reduce the risk, extent and severity of these events,particularly in the wildland–urban interface. In this study, we examined the effects of mechanical fuel reduction treatments on the activity of barkbeetles in ponderosa pine, Pinus ponderosa Dougl ex. Laws., forests located in Arizona and California, USA. Treatments were applied in both latespring (April–May) and late summer (August–September) and included: (1) thinned biomass chipped and randomly dispersed within each 0.4 haplot; (2) thinned biomass chipped, randomly dispersed within each plot and raked 2 m from the base of residual trees; (3) thinned biomass lopped-and-scattered (thinned trees cut into 1–2 m lengths) within each plot; (4) an untreated control. The mean percentage of residual trees attacked bybark beetles ranged from 2.0% (untreated control) to 30.2% (plots thinned in spring with all biomass chipped). A three-fold increase in thepercentage of trees attacked by bark beetles was observed in chipped versus lopped-and-scattered plots. Bark beetle colonization of residual treeswas higher during spring treatments, which corresponded with peak adult beetle flight periods as measured by funnel trap captures. Raking chipsaway from the base of residual trees did not significantly affect attack rates. Several bark beetle species were present including the roundheadedpine beetle, Dendroctonus adjunctus Blandford (AZ), western pine beetle, D. brevicomis LeConte (AZ and CA), mountain pine beetle, D.ponderosae Hopkins (CA), red turpentine beetle, D. valens LeConte (AZ and CA), Arizona fivespined ips, Ips lecontei Swaine (AZ), Californiafivespined ips, I. paraconfusus Lanier (CA) and pine engraver, I. pini (Say) (AZ). Dendroctonus valens was the most common bark beetle infestingresidual trees. A significant correlation was found between the number of trees chipped per plot and the percentage of residual trees with D. valensattacks. A significantly higher percentage of residual trees was attacked by D. brevicomis in plots that were chipped in spring compared to theuntreated control. In lopped-and-scattered treatments, engraver beetles produced substantial broods in logging debris, but few attacks wereobserved on standing trees. At present, no significant difference in tree mortality exists among treatments. A few trees appeared to have died solelyfrom D. valens attacks, as no other scolytids were observed in the upper bole. In a laboratory study conducted to provide an explanation for the barkbeetle responses observed in this study, monoterpene elution rates from chip piles declined sharply over time, but were relatively constant inlopped-and-piled treatments. The quantities of b-pinene, 3-carene, a-pinene and myrcene eluting from chips exceeded those from lopped-and-piled slash during each of 15 sample periods. These laboratory results may, in part, explain the bark beetle response observed in chippingtreatments. The implications of these results to sustainable forest management are discussed.Published by Elsevier B.V.Keywords: Chipping; Lop-and-scattering; Slash management; Monoterpenes; Pinus ponderosa; Scolytidae; Dendroctonus valens; Dendroctonus brevicomis1. IntroductionDendrochronological research in many western NorthAmerican coniferous forests indicates a pine-dominated covertype that was open and park-like, large-tree dominated andshaped by frequent low-intensity fires prior to Europeansettlement (Agee, 1993, 1994; Agee and Skinner, 2005;Covington and Moore, 1994; Skinner and Chang, 1996; Taylor,www.elsevier.com/locate/forecoForest Ecology and Management 230 (2006) 55–68* Corresponding author at: Pacific Southwest Research Station, USDA ForestService, 1107 Kennedy Place, Suite 8, Davis, CA 95616, USA.Tel.: +1 530 758 5151; fax: +1 530 758 5155.E-mail address: [email protected] (C.J. Fettig).0378-1127/$ – see front matter. Published by Elsevier B.V.doi:10.1016/j.foreco.2006.04.0182000; Swetnam and Baisan, 2002; Stephen et al., 2003).Compared to their historical counterparts, these forests are nowmuch denser, have more smaller trees and fewer larger trees andare dominated by more shade-tolerant and fire-intolerant treespecies (Hessburg and Agee, 2003). Many areas that werepreviously open have become forested (Skinner, 1995; Normanand Taylor, 2005 ). These conditions have led to increases incompetition among trees for below-ground nutrients, water andgrowing space, thereby increasing vulnerability of such foreststo bark beetles (Coleoptera: Scolytidae) and other forest insectsand diseases (Ferrell et al., 1994; Oliver, 1995; Oliver andLarson, 1996). Bark beetles are a major cause of tree mortalityin ponderosa pine , Pinus ponderosa Dougl ex. Laws., forests(Furniss and Carolin, 1977). Extensive amounts of bark beetle-caused tree mortality may exacerbate problems associated withheavy fuel loads (Covington and Moore, 1994).Forest fuels are generally classified into three components:ground fuels, surface fuels, and understory and overstory fuels(Agee and Skinner, 2005). Ground fuels include newly castmaterial