Doctoral Dissertation Research: Climate Variability and the Susceptibility of Engelmann Spruce to Spruce Beetle (Dendroctonus Rufipennis) Outbreaks in Northwestern Colorado

这个博士论文研究项目将调查温暖的温度对云杉树的易感性云杉甲虫在北美西部的亚高山环境中的侵扰的影响。 20世纪末和21世纪初的气候变化被广泛认为是北美西部树皮甲虫活动急剧增加的主要驱动力。虽然在过去的二十年里，山松甲虫（MPB; Dendroctonus ponderosae）已经引起了北美大部分与树皮甲虫相关的树木死亡率，但人们越来越担心云杉甲虫（SB; Dendroctonus rufipennis）的爆发可能同样广泛。科罗拉多和怀俄明州受SB影响的面积几乎翻了一番，从2009年的460平方公里增加到2010年的840平方公里。在过去二十年中，这种和其他树皮甲虫爆发的广泛程度和大量死亡率与甲虫种群动态研究得出的预测一致，该研究预测，温暖的气候通过降低冬季死亡率和从两年到一年的生命周期转变来刺激甲虫活动。然而，相对知之甚少的SB活动所造成的空间变异云杉树的易感性，介导的物理环境因素与森林动态相互作用，以应对以前的干扰火，风，和过去的爆发。早期的研究表明，树的易感性的变化可能限制了以前的SB爆发的程度和严重程度，但树的易感性对爆发动态的反馈似乎大大减少了当前爆发（1998年至今）的温暖气候下。 该项目的中心目标是确定在气候变化的背景下，在复杂的亚高山环境的科罗拉多西北部的安格曼云杉（云杉）树SB爆发的敏感性。通过GIS和树木年轮分析，该研究试图重建历史和当代SB爆发。 该研究旨在回答以下两个研究问题：与科罗拉多西北部历史性云杉甲虫爆发有关的气候条件是什么？ 2)什么非生物和生物因素决定敏感性当前时期的SB攻击在树和立场的水平，以及如何比较这些关系与历史的关系（1998年前）之间的敏感性SB和相同的变量？这项研究的结果将提供深入了解气候变化如何改变云杉树SB爆发在北美亚高山环境的敏感性。进一步了解气温升高、甲虫侵扰和其他森林动态之间的关系，将有助于为管理决策提供信息，并评估与树木高死亡率有关的对附近社区的危害。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立的研究生涯。

This doctoral dissertation research project will investigate the effects of warmer temperatures on the susceptibility of spruce trees to infestations by spruce beetles in subalpine environments of western North America. Changes in climate during the late 20th and early 21st centuries are widely viewed as the primary driver of a dramatic increase in bark beetle activity throughout western North America. Although the mountain pine beetle (MPB; Dendroctonus ponderosae) has caused most bark beetle related tree mortality across North America over the past two decades, concern has been growing that outbreaks of the spruce beetle (SB; Dendroctonus rufipennis) could be similarly extensive. The area affected by SB in Colorado and Wyoming nearly doubled from 460 km2 in 2009 to 840 km2 in 2010. The vast extent and substantial mortality of this and other bark beetle outbreaks over the last two decades are consistent with predictions drawn from studies of beetle population dynamics, which predict that a warmer climate stimulates beetle activity through decreased winter mortality and shifts from two-year to one-year life cycles. However, comparatively little is known about the potential constraints on SB activity posed by spatial variation in spruce tree susceptibility, as mediated by physical environmental factors interacting with forest dynamics in response to previous disturbances by fire, wind, and past outbreaks. Early research suggests that variation in tree susceptibility may have limited the extent and severity of previous SB outbreaks, but the feedback of tree susceptibility on outbreak dynamics appears to be greatly reduced under the warmer climate of the current outbreak (1998 - present). The central goal of this project is to determine the susceptibility of Engelmann spruce (Picea engelmannii) trees to SB outbreaks across the complex subalpine environment of northwestern Colorado in the context of climate variability. Using an integration of mapping via GIS as well as tree-ring analysis the research seeks to reconstruct historical and contemporary SB outbreaks. The research seeks answers to the following two research questions: What are the climate conditions related to historic spruce beetle outbreaks in northwestern Colorado? 2) What abiotic and biotic factors determine susceptibility to the current period of SB attack at the tree and stand-level, and how do these relationships compare with historic relationships (pre-1998) between susceptibility to SB and the same variables?The results of this research will provide insight into how climate variability alters the susceptibility of spruce trees to SB outbreak across the subalpine environment in North America. An increased understanding of the relationships between increased temperatures, beetle infestations and other forest dynamics will help inform management decisions and evaluate hazards to nearby communities related to high tree mortality. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.