Longitudinal variation in the physiology, growth and reproduction of white spruce at the Arctic treeline in Alaska

北极林线的位置是高纬度环境中地表能源预算、碳循环、栖息地可用性和生存资源的重要调节器。北极森林的健康和空间范围的变化很大程度上取决于气候与树木的生理、生长和繁殖成功率之间的关系。先前沿着阿拉斯加布鲁克斯山脉的纵向梯度进行的研究显示，随着从西向东气温上升，植物生长下降的模式。这项研究旨在揭示这一趋势背后的过程，并研究对繁殖成功和在当前林线之外建立新树木的影响。其目标是测量和比较布鲁克斯山脉西部、中部和东部的树木小气候；比较和对比布鲁克斯山脉西部、中部和东部几个生长季节白云杉冠层气体交换的连续测量，以评估阿拉斯加北极林线干旱胁迫和寒冷土壤的相对重要性；详细测量布鲁克斯山脉西部、中部和东部白云杉所有主要器官的季节性和生长幅度，评估分配变化的潜力，并更准确地评估当前和未来的树木表现；对布鲁克斯山脉内种子产量、种子质量、幼苗建立和幼苗表现（生理和生长）的纵向变化进行详细研究，因为这些人口统计过程将在很大程度上决定林线是否会因气候变化而前进、保持静止或后退。研究结果将告知政策制定者和当地居民气候变化与阿拉斯加高度敏感的北极森林的健康和空间范围之间相互作用的可能结果。该团队将通过四项具体活动接触阿拉斯加农村和城市的学生和成年人。他们将扩大与科策布高中生物教师的现有关系，并参观他们的教室，介绍植被作为气候变化调解者的重要性，并分享该地区之前和正在进行的工作成果。他们将为 Kotzebue 高中的优秀学生提供加入库古鲁罗克现场研究团队的机会。他们将安排接受 Kotzebue 公共广播电台的采访，向社区通报他们的研究活动和发现，并且他们将参加 BLM 坎贝尔溪科学中心炉边聊天系列。

The position of the Arctic treeline is an important regulator of surface energy budgets, carbon cycling, habitat availability and subsistence resources in high latitude environments. Changes in the health and spatial extent of the arctic forest are largely governed by relationships among climate and the physiology, growth and reproductive success of the trees. Previous work along a longitudinal gradient in the Brooks Range, Alaska, showed a pattern of declining growth in response to rising temperatures from west to east. This study aims to uncover the processes underlying this trend and examine the implications for reproductive success and the establishment of new trees beyond the current treeline. Its goals are to measure and compare tree microclimates of the western, central and eastern Brooks Range; compare and contrast continuous measurements of white spruce canopy gas exchange over several growing seasons in the western, central and eastern Brooks Range in order to evaluate the relative importance of drought stress and cold soils at the arctic treeline in Alaska; make detailed measurements of the seasonality and magnitude of growth in all major organs of white spruce in the western, central and eastern Brooks Range, assess the potential for shifts in allocation and to more accurately evaluate current and future tree performance; and conduct a detailed study of longitudinal variation in seed production, seed quality, seedling establishment and seedling performance (physiology and growth) within the Brooks Range, as these demographic processes will largely determine whether a treeline will advance, remain static or retreat in response to climate change. Results of the study will inform policy makers and local residents of the likely outcomes of interactions between climate change and the health and spatial extent of the highly sensitive arctic forests of Alaska.The team will reach out to students and adults in rural and urban Alaska through four specific activities. They will extend an existing relationship with biology teachers at Kotzebue High School and visit their classrooms to introduce the importance of vegetation as a mediator of climate change and to share the results of previous and ongoing work in the area. They will provide opportunities for outstanding students from Kotzebue High School to join their research team in the field at the Kugururok site. They will arrange to be interviewed by Kotzebue Public Radio to inform the communities about their research activities and findings, and they will participate in a BLM Campbell Creek Science Center Fireside Chat series.