Collaborative Research: Assessing the Use of Paleorecords to Understand Beetle Outbreaks in Subalpine Forests

在过去的半个世纪里，由于气候和人类活动的变化，西部森林生态系统的干扰状况发生了重大变化。 虽然人们把注意力集中在火灾和洪水等干扰上，但爆发性树皮甲虫物种对西部森林社区的影响相当或更大。 像所有昆虫一样，树皮甲虫对温度的轻微变化非常敏感，最近的变暖趋势可能导致爆发频率增加，范围扩大到以前未被甲虫占据的环境，如高海拔和高纬度森林。 山松甲虫的爆发在低海拔的黑松林中更常见，但在白皮松生态系统中被认为是相对罕见的事件。 白皮松中山松甲虫的爆发可能有些新奇，在二十世纪只有少数记录的爆发。 然而，近年来，山松甲虫爆发似乎更频繁地发生在白皮松森林。 最近在白皮松森林中广泛出现的山松甲虫可能是气候变暖引起的山松甲虫生活史特征变化或宿主易感性变化的结果。 森林中山地松甲虫的长期动态以及气候变异的潜在作用仍然鲜为人知，因为爆发并不频繁，历史记录很少超过二十世纪。 这就限制了可以审查的事件的数量，并妨碍了对造成疾病暴发的潜在机制的研究。 这项合作研究项目将使用古生态重建方法增加两个流域的山松甲虫爆发记录。 研究人员将校准常见的（如lodgepole松）和潜在的新的（如白皮松）森林生态系统的山松甲虫爆发的历史记录，通过将树木年代学技术与湖泊沉积物分析相结合，进一步追溯爆发的历史。 这两种古生态重建方法的使用利用了每种方法的主要优势-树木年轮提供的年度分辨率和可以从湖泊沉积物中收集的非凡的时间深度，这些沉积物通常超过几千年。 研究人员将开发森林演替模式的详细记录后，最近的山松甲虫爆发使用树木年轮与更长的记录植被和干扰历史的花粉和昆虫遗骸中发现的湖泊沉积物进行比较。 每年解决重建夏季温度将开发使用温度敏感的树木年轮记录，以评估与树皮甲虫爆发的气候模式的作用。 从树木年轮中得到的演替模式、气候变化和甲虫活动的记录将与湖泊沉积物记录进行比较，在湖泊沉积物记录中，替代物在时间上重叠，以校准沉积物记录，并进一步改善对过去的解释。 首先，该项目将调查潜在的使用代理记录重建过去的山松甲虫爆发。 第二，该项目将提供一种新的花粉分析方法，包括比较仪器和树木年代学重建的气候。 对花粉与近1,000年来树木年轮重建的气候之间关系的校准，将加强对无法获得仪器和树木年代学数据的时期气候条件的推断。 第三，结果将被用来分析森林演替动态山松甲虫爆发，并提供有关如何植被组成可能会改变山松甲虫虫害的结果。 除了对甲虫爆发、森林演替和气候控制科学做出贡献外，这项研究还将直接应用于管理。 这项研究将确定山松甲虫爆发与夏季气候条件之间的联系，可用于更好地为负责在气候变化的情况下制定森林可持续性计划的管理人员提供信息。 白皮松是这些生态系统中的关键物种，目前正面临着许多威胁，包括山松甲虫活动的潜在增加。 了解气候，植被和山松甲虫如何在长时间尺度上相互作用，将为管理人员提供关键信息，以制定管理计划，减轻气候变化的有害影响。 研究人员将在整个研究过程中与资源管理人员密切合作，使研究结果易于获得，以便管理人员在研究进展时了解研究情况，并及时使用重要的研究结果。

The last half-century has witnessed substantial alterations in the disturbance regimes of western forest ecosystems resulting from both changes in climate and human activities. While much attention is being focused on disturbances like fire and floods, eruptive bark beetle species have had equal or greater impact on western forest communities. Like all insects, bark beetles are highly sensitive to slight shifts in temperature, and recent warming trends may have resulted in increased outbreak frequency and range expansion into environments that were previously unoccupied by the beetles, such as high-elevation and high-latitude forests. Mountain pine beetle outbreaks are more common in lower elevation lodgepole pine forests but are thought to be relatively rare events in whitebark pine ecosystems. Outbreaks of mountain pine beetle in whitebark pine may be somewhat novel, with only a few documented outbreaks over the twentieth century. In recent years, however, mountain pine beetle outbreaks appear to be occurring more frequently in whitebark pine forests. The recent widespread appearance of mountain pine beetle in whitebark pine forests may be the result of changes to the life-cycle characteristics of mountain pine beetle or host susceptibility brought about by a warming climate. The long-term dynamics of mountain pine beetles in forests and the potential role of climate variability remains little understood because outbreaks are infrequent and historical records rarely extend beyond the twentieth century. This limits the number of events that can be examined and hinders the search for potential mechanisms producing outbreaks. This collaborative research project will increase the record of mountain pine beetle outbreaks in two watersheds using paleoecological reconstruction methods. The investigators will calibrate the historical record of mountain pine beetle outbreaks in common (e.g. lodgepole pine) and potentially novel (e.g. whitebark pine) forest ecosystems to extend outbreak histories further back in time by integrating dendrochronological techniques with lake sediment analyses. The use of these two paleoecological reconstruction methodologies takes advantage of the main strengths of each -- the annual resolution afforded by tree rings and the extraordinary depth of time that can be gleaned from lake sediments, which often exceed several thousand years. The investigators will develop detailed records of forest successional patterns following the most recent mountain pine beetle outbreaks using tree rings for comparison with longer records of vegetation and disturbance history available from pollen and insect remains found in lake sediments. Annually resolved reconstructions of summer temperature will be developed using tree-ring records from temperature sensitive trees to assess the role of climatic patterns related to bark beetle outbreaks. Records of successional patterns, climate variability, and beetle activity developed from tree rings will be compared with lake sediment records where the proxies overlap temporally to calibrate the sediment record and improve interpretations further into the past.The results of this project will be relevant to management efforts in the forests where the study is conducted, and they will provide a number of longer-term benefits. First, the project will investigate the potential use of proxy records to reconstruct past mountain pine beetle outbreaks. Second, the project will provide a new method of pollen analysis that includes comparisons between instrumental and dendrochronological reconstructions of climate. The calibration of relationships between pollen and reconstructed climate from tree rings for approximately the last 1,000 years will strengthen inferences of climate conditions for periods of time for which instrumental and dendrochronological data are not available. Third, the results will be used to analyze forest successional dynamics following mountain pine beetle outbreaks and provide information regarding how vegetation composition may shift as a result of mountain pine beetle infestations. In addition to contributing to the science of beetle outbreaks, forest succession and climate controls, there will be direct management applications as a result of the research. The study will identify the linkages between mountain pine beetle outbreaks and summer climate conditions that can be used to better inform management personnel charged with developing plans for forest sustainability in the face of a changing climate. Whitebark pine is a keystone species in these ecosystems and is currently facing a number of threats including potential increases in mountain pine beetle activity. Understanding how climate, vegetation, and mountain pine beetles interact at long time scales will provide managers with critical information to develop management plans that could mitigate the deleterious impacts of a changing climate. The investigators will make the results accessible by working closely with resource managers throughout the study so that the managers are aware of the research as it progresses and can use significant findings in a timely manner.