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

这项博士论文研究项目将调查在北美西部亚高山环境中，气温变暖对云杉树对云杉甲虫侵染的影响。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。尽管在过去的20年里，山松甲虫(Dendroctonus Ponderosae)在北美造成了大多数与树皮甲虫相关的树木死亡，但人们越来越担心云杉甲虫(Dendroctonus Rufipennis)的暴发可能同样广泛。科罗拉多州和怀俄明州受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。过去20年来，这种和其他树皮甲虫暴发的广泛范围和相当大的死亡率与甲虫种群动态研究得出的预测是一致的，这些预测预测，气候变暖通过降低冬季死亡率来刺激甲虫的活动，并从两年的生命周期转变为一年的生命周期。然而，云杉敏感度的空间变异对SB活性的潜在制约作用相对较少，这种限制是由物理环境因素与森林动态相互作用对先前的火、风和以往暴发的干扰所调节的。早期研究表明，树木易感性的变化可能限制了以前SB暴发的范围和严重程度，但在当前(1998年至今)气候变暖的情况下，树木易感性对暴发动态的反馈似乎大大减少。该项目的中心目标是确定在气候多变性的背景下，在科罗拉多州西北部复杂的亚高山环境中，恩格尔曼云杉(Picea Engelmannii)树木对SB爆发的敏感性。利用地理信息系统测绘和树轮分析相结合的方法，这项研究试图重建历史和当代的SB暴发。这项研究寻求以下两个研究问题的答案：什么是与科罗拉多州西北部历史上云杉甲虫暴发有关的气候条件？2)什么非生物和生物因素决定了当前时期树木和林分水平上SB攻击的易感性，以及这些关系与历史上(1998年之前)对SB易感性和相同变量之间的关系如何？这项研究的结果将为深入了解气候变化如何改变北美亚高山环境中云杉对SB爆发的易感性提供洞察。更多地了解气温升高、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，并评估与高树木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.