Doctoral Dissertation Research: Calibration and Application of Sedimentary Proxies in Evaluating Spruce Beetle Outbreaks from the High Plateaus of Utah

树皮甲虫（Dendroctonus spp.）和野火是北美西部针叶林的重要干扰因子。了解其发生、生态意义以及这两种干扰在长时间尺度和不同气候条件下如何相互作用，对于了解当前森林动态具有重要意义。现有的方法是利用湖泊沉积物中的沉积木炭重建全新世（过去~1万年）过去的火灾事件。然而，尽管树皮甲虫具有重要的生态意义，但目前还没有方法可以利用湖泊沉积物在类似的时间尺度上评估树皮甲虫的干扰。亚高山森林对云杉甲虫侵害的生态响应通常是亚高山冷杉（冷杉）和其他林下成分在成熟云杉死亡后丰度和生产力增加。林下植被的旺盛生长归因于阳光、水分和养分的增加。历史林分清查数据和树木年轮记录都充分记录了严重暴发后林下成分的“释放”。这些林分结构的变化反映在花粉记录中。利用从犹他州六个亚高山盆地获得的花粉记录，进行了一项校准研究，强调花粉沉积的变化与20世纪几次云杉甲虫（D. rufipennis）爆发同时发生。这些变化通常反映了杉木和其他林下分类群的云杉花粉交换。该研究支持的研究将应用于位于犹他州中部和南部的Wasatch高原、Markagunt高原和Aquarius高原的三个全新世长度沉积物岩心的花粉数据。Markagunt高原遗址是最具时间分辨率的核心，将以多年代际分辨率进行年代测定和分析，以进一步完善与云杉甲虫侵扰相关的森林动态。该项目将为利用湖泊沉积物重建亚高山森林云杉甲虫的非火干扰提供重要的一步。建立森林生态和干扰的长期记录是土地管理者及其相关机构的重要资源。在这里进行的研究将为解释最近西部针叶林中树皮甲虫的爆发提供重要的理解基线。本研究通过博士论文研究进步奖的支持，将使有前途的学生建立一个强大的环境研究事业。

Bark beetles (Dendroctonus spp.) and wildfire are significant disturbance agents in conifer forests of western North America. Understanding the occurrence, the ecological significance and how these two disturbances interact over long time scales and under different climatic regimes is import to contextualize current forest dynamics. Methodologies exist for reconstructing past fire episodes over the Holocene (last ~10,000 years) using sedimentary charcoal from lake sediments. However, no methodology currently exists for assessing bark beetle disturbances over similar timescales using lake sediments, despite their ecological significance. The ecological response of subalpine forests to a spruce beetle infestation is generally that subalpine fir (Abies lasiocarpa) and other understory components increase in abundance and productivity following mortality of mature spruce. The invigorated growth of the understory is attributed to increased availability of sunlight, moisture and nutrients. The 'release' of the understory component following severe outbreaks is well documented in historic stand inventory data as well as in tree ring records. These changes in stand structure are reflected in the pollen record. Using pollen records obtained from six subalpine basins in Utah, a calibration study was performed emphasizing changes in pollen deposition concurrent with several 20th century spruce beetle (D. rufipennis) outbreaks. These changes generally reflect an exchange of spruce pollen for fir and other understory taxa. The research supported here will apply the calibration set to pollen data from three Holocene-length sediment cores retrieved from the Wasatch Plateau, Markagunt Plateau and Aquarius Plateau, located in central and southern Utah. The Markagunt Plateau site is the most temporally resolved core and will be dated and analyzed at multidecadal resolution to further refine forest dynamics associated with spruce beetle infestations.This project will provide an important step forward in using lake sediments to reconstruct non-fire disturbances, specifically for spruce beetle in subalpine forests. Developing long term records of forest ecology and disturbance are important resources for land managers and their respective agencies. The research conducted here will provide an important baseline of understanding with which to interpret recent bark beetle outbreaks in western conifer forests. The support of this research through a Doctoral Dissertation Research Improvement award will enable a promising student to establish a strong environmental research career.