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

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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.