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

松毛虫(Dendroctonus spp.)和野火是北美西部针叶林的重要干扰因子。了解这两种干扰的发生、生态意义以及这两种干扰如何在长时间尺度和不同气候制度下相互作用，对于了解当前森林动态具有重要意义。利用湖泊沉积物中的沉积木炭重建全新世(最近10,000年)过去的火灾事件的方法已经存在。然而，目前还不存在使用湖泊沉积物在类似时间尺度上评估树皮甲虫干扰的方法，尽管它们具有生态意义。亚高山森林对云杉甲虫侵染的生态响应一般是随着成熟云杉的死亡，亚高山冷杉和其他林下成分的丰富度和生产力增加。林下植被的活跃生长归功于阳光、水分和养分的增加。林下成分在严重暴发后的“释放”在历史林分清查数据以及年轮记录中都有很好的记录。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，重点是在20世纪几次云杉甲虫(D.rufipennis)暴发的同时，花粉沉积的变化。这些变化通常反映了云杉花粉与冷杉和其他林下分类群的交换。这里支持的研究将把定标集应用于从犹他州中部和南部的瓦萨奇高原、马卡贡高原和宝瓶座高原提取的三个全新世沉积岩芯的花粉数据。马卡贡高原遗址是时间分辨率最高的核心，将以数十年的分辨率进行测年和分析，以进一步完善与云杉甲虫侵袭相关的森林动态。该项目将在利用湖泊沉积物重建非火灾干扰方面向前迈出重要的一步，特别是对于亚高山森林中的云杉甲虫。建立森林生态和干扰的长期记录是土地管理者及其各自机构的重要资源。这里进行的研究将提供一个重要的理解基线，用来解释最近在西部针叶林中爆发的树皮甲虫。通过博士论文研究改进奖支持这项研究将使一个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.