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

在过去的半个世纪里，由于气候变化和人类活动，西部森林生态系统的干扰机制发生了重大变化。虽然人们的注意力都集中在火灾和洪水等干扰上，但爆发树皮甲虫物种对西部森林群落产生了同等或更大的影响。像所有昆虫一样，树皮甲虫对温度的轻微变化高度敏感，最近的变暖趋势可能导致爆发频率增加，范围扩大到以前没有甲虫居住的环境，如高海拔和高纬度的森林。山松甲虫的爆发在低海拔的黑松林中更为常见，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颖，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林。近年来在白皮松林中广泛出现的山松甲虫，可能是气候变暖导致山松甲虫生活史特征改变或寄主易感的结果。森林中山松甲虫的长期动态和气候变化的潜在作用仍然知之甚少，因为暴发不频繁，历史记录很少超过20世纪。这限制了可以检查的事件数量，并妨碍了寻找产生疫情的潜在机制。本合作研究项目将利用古生态重建方法增加两个流域山松甲虫爆发的记录。研究人员将通过将树木年代学技术与湖泊沉积物分析相结合，校准常见（如黑松）和潜在的新型（如白皮松）森林生态系统中山松甲虫爆发的历史记录，从而将爆发历史进一步追溯到过去。使用这两种古生态重建方法利用了各自的主要优势——树木年轮提供的年度分辨率和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。研究人员将利用树木年轮与湖泊沉积物中发现的花粉和昆虫遗骸中较长的植被记录和干扰历史进行比较，详细记录最近山松甲虫爆发后的森林演替模式。利用对温度敏感的树木的年轮记录，将开发夏季温度的年度分解重建，以评估与树皮甲虫爆发有关的气候模式的作用。从树木年轮中得到的演替模式、气候变率和甲虫活动记录将与湖泊沉积物记录进行比较，其中代用物在时间上重叠，以校准沉积物记录并进一步改进对过去的解释。这个项目的结果将与进行研究的森林的管理工作有关，并将提供若干长期利益。首先，该项目将调查代理记录的潜在用途，以重建过去的山松甲虫爆发。其次，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。根据树木年轮对花粉和重建气候之间的关系进行校准，这将加强对没有仪器和树木年代学数据的时期的气候条件的推断。第三，研究结果将用于分析山松甲虫爆发后的森林演替动态，并提供关于山松甲虫侵袭如何导致植被组成变化的信息。除了有助于甲虫爆发、森林演替和气候控制的科学研究外，这项研究还将有直接的管理应用。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，可以用来更好地向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，将为管理者提供关键信息，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，使结果易于获取，以便管理人员了解研究的进展情况，并及时使用重要的发现。

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.