Gadd, Teri, authorDavis, Seth, advisorNegrón, Jose, committee memberKlett, Jim, committee memberRedmond, Miranda, committee member2022-01-072024-01-062021https://hdl.handle.net/10217/234312Bark beetle outbreaks have caused adverse economic and lumber deficiencies impacting 10.3 million ha since 2000 (Cochran and Barrett 1993; Fettig 2021; Lindgren and Raffa 2013). A common bark beetle management method is to reduce basal area. Reducing within-stand competition may improve individual tree vigor but also can alter stand-level resistance to beetles. Some studies have also shown that density reduction treatments can have deleterious effects on tree resistance. Lodgepole pine trees (Pinus contorta Douglas ex Loudon var. latifolia Engelman) across the northern Rocky Mountains have been killed in increasingly severe mountain pine beetle (Dendroctonus ponderosae, Hopkins, MPB) outbreaks. Accordingly, there is a need to fine-tune cultural control methods at a regional scale in order to determine how to best manage forest stands for reduced bark beetle damage. Here, we exploit an outbreak of the mountain pine beetle (Dendroctonus ponderosa) in northern Colorado to evaluate basal area reduction treatments (BART) of 21, 42, 63, and 95 m2/ha, (hereafter referred to as BART21, BART42, BART63, and UBA95) of lodgepole pine (Pinus contorta Douglas ex Loudon var. latifolia Engelman) over three studies. In study one, we examined BART impacts on microsite conditions. Conclusions that can be drawn from this research are (1) the positive and negative consequences of thinning treatments in a resource allocation system; response from thinning can spur RAI and height, increase phloem thickness, increase water and photosynthate maintenance demands, reduce allocation to defense and future foliar biomass, increase preference for beetle attack, increase temperature and humidity, reduce localized terpene and kairomone concentrations, (2) natural, non-baited studies are more variable than baited, closed chamber, and lab studies, (3) single parameter beetle studies fail to capture the complex interwoven nature of beetle-tree-stand ecosystems, (4) RAI & height respond best to thinning treatments, (5) when beetle numbers are high enough, management method may not matter, and (6) tree and soil water, while important for growth and increased resin exudation pressure, are less important on a stand level but show an effect on individual tree survival and insect damage rating. In study two, we examined two measures of water stress with BART. Conclusions that can be drawn from this research are (1) beetle attack and tree water stress interactions within complex interwoven beetle-tree-stand ecosystems are better understood using multiple physiological, environmental, and biotic parameters (2) tree and soil water, while important for growth and MPB defense, are less impactful on a stand level, but show an effect on individual tree survival, (3) RAI & height respond best to thinning treatments, (4) thinning treatments have both positive and negative consequences: they can improve tree vigor and defenses, but they can also spur RAI and escalate DBH into preferred size for MPB attack. Managers should be careful about how they prescribe treatments because it is possible that BARTs can have outcomes that are not desirable. Both daily and seasonal measures of needle water stress, in a more comprehensive study, need to be examined to pinpoint the effects of tree level water, physiological parameters, and the interface with MPB. In study three, we concurrently measured the effects of BART on tree needle monoterpene profiles, tree water stress, and MPB attack behavior over two years during a MPB outbreak to make a small contribution of understanding more about the interaction between lodgepole pine physiology, anthropogenic forest management, and MPB. Conclusions that can be drawn from this research are (1) BART is an effective management method to alter terpene proportions, (2) BART will not impact each terpene proportion the same, (3) Day-of-year is a key factor in terpene proportions, (4) year is only a factor in 10% of terpene proportions, (5) water stress may impact only select terpene proportions (6) the proportion of α-pinene does not have a bearing on attack status, whereas the proportions of β-pinene, 3-carene, α-phellandrene, and limonene do. While not tested here, these results may also have some significance for defoliating insects and wildfires.born digitaldoctoral dissertationsengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.lodgepole pineterpeneswater stressmountain pine beetle13C isotopetree physiologyText