OOS 38
Advancing Knowledge of Alpine and Arctic Treeline Ecotones and Responses to Environmental Change

Thursday, August 14, 2014: 8:00 AM-11:30 AM
307, Sacramento Convention Center
Lara Kueppers, University of California Merced
David M. Cairns, Texas A&M University; Melanie A. Harsch, University of Washington; and Constance I. Millar, USDA Forest Service, Pacific Southwest Research Station
Lara Kueppers, University of California Merced
Treeline research has been advancing rapidly, motivated in part by the need to predict land surface feedbacks to regional and global climate change, water resources in mountain regions, and impacts of environmental change on high latitude and high elevation biodiversity. Upper elevation and northern treeline ecotones are boundary zones between forest and arctic or alpine treeless zones. Although presence of upright trees has defined the treeline per se, treeline is more accurately described as an ecotone structured by complex interactions among vegetation, soils, animals, climate, snow, topography, and disturbance regimes. Responses of this ecotone to environmental change have been observed, but complex lags and feedbacks -- in addition to topographic influences that confound of responses in mountain treelines -- challenge predictions of change. This session brings together diverse perspectives and expertise in treeline research to report recent advances, both in basic understanding of treeline dynamics and in predicting responses of alpine and arctic treelines to environmental change. By including talks from diverse subfields in ecology the session seeks to foster new collaborations and insights that will advance integrative science of the treeline ecotone. A further objective is to bridge the historical divide between arctic and alpine treeline research. The session comprises ten talks on different aspects of treeline research: paleoclimate and paleoecology, tree demography, ecophysiology, modeling treeline, plant-animal interactions, experimental ecology, ecosystem processes, and the role of disturbance in structuring treeline. Speakers represent the international nature of treeline research and work in both arctic and alpine treeline ecotones.
8:00 AM
 Physiological explanations of current and future treeline positions require a stringent treeline definition
Günter Hoch, Institute of Botany, University of Basel; Christian Koerner, University of Basel
8:20 AM
 From source- to sink limited vegetation modelling
Sebastian Leuzinger, Auckland University of Technology; Simone Fatichi, ETH Zurich; Corina Manusch, ETH Zurich; Harald Bugmann, ETH Zurich; Annett Wolf, University of Umea; Christian Körner, University of Basel
8:40 AM
 Soil nutrient availability constrains growth and allocation of treeline trees in northwest Alaska
Patrick F. Sullivan, University of Alaska Anchorage; Robert W. McNown, University of Alaska Anchorage; Annalis H. Brownlee, University of Alaska Anchorage; Sarah B.Z. Ellison, University of Alaska Anchorage; Bjartmar Sveinbjornsson, University of Alaska Anchorage
9:00 AM
 The impact of herbivory within the treeline ecotone
James D. M. Speed, Norwegian University of Science and Technology; Gunnar Austrheim, Norwegian University of Science and Technology; Alison J. Hester, James Hutton Institute; Øystein Holand, Norwegian University of Life Sciences; Atle Mysterud, University of Oslo
9:20 AM
 Fire effects on boreal treeline responses to climate change
Jill F. Johnstone, University of Saskatchewan; Carissa D. Brown, Memorial University
9:40 AM
10:10 AM
 Climate isn't everything: Biotic interactions, life stage, and seed origin will also affect range shifts in a warming world
Ailene Ettinger, Arnold Arboretum of Harvard University; Janneke HilleRisLambers, University of Washington
11:10 AM
 Getting to the root of the matter: The role of mycorrhizal fungi in post-fire seedling establishment at treeline
Rebecca E. Hewitt, University of Alaska Fairbanks; Michelle C. Mack, University of Florida; D. Lee Taylor, University of New Mexico; Teresa N. Hollingsworth, Pacific Northwest Research Station; F. Stuart Chapin III, University of Alaska Fairbanks