Evidence and implications of recent and projected climate change in Alaska’s forest ecosystems 1, 2 1 3 4 JANE M. WOLKEN, TERESA N. HOLLINGSWORTH, T. SCOTT RUPP, F. STUART CHAPIN, III, SARAH F. TRAINOR, 5 6 7 3 8 TARA M. BARRETT, PATRICK F. SULLIVAN, A. DAVID MCGUIRE, EUGENIE S. EUSKIRCHEN, PAUL E. HENNON, 9 10 11 8 1 ERIK A. BEEVER, JEFF S. CONN, LISA K. CRONE, DAVID V. D ’AMORE, NANCY FRESCO, 8 3 12 11 13 THOMAS A. HANLEY, KNUT KIELLAND, JAMES J. KRUSE, TRISTA PATTERSON, EDWARD A. G. SCHUUR, 14 14 DAVID L. VERBYLA, AND JOHN YARIE 1Scenarios Network for Alaska and Arctic Planning, University of Alaska, 3352 College Road, Fairbanks, Alaska 99709 USA 2United States Department of Agriculture Forest Service, Pacific Northwest Research Station, Boreal Ecology Cooperative Research Unit, P.O. Box 756780, University of Alaska, Fairbanks, Alaska 99775 USA 3Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775 USA 4Alaska Center for Climate Assessment and Policy, University of Alaska, 3352 College Road, Fairbanks, Alaska 99709 USA 5United States Department of Agriculture Forest Service, Pacific Northwest Research Station, Anchorage Forestry Sciences Laboratory, 3301 C Street, Suite 200, Anchorage, Alaska 99503 USA 6Environment and Natural Resources Institute, Department of Biological Sciences, University of Alaska, Anchorage, Alaska 99508 USA 7United States Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska, Fairbanks, Alaska 99775 USA 8United States Department of Agriculture Forest Service, Pacific Northwest Research Station, Juneau Forestry Sciences Laboratory, 11305 Glacier Highway, Juneau, Alaska 99801 USA 9Northern Rocky Mountain Science Center, United States Geological Survey, Bozeman, Montana 59715 USA 10Agricultural Research Service, United States Department of Agriculture, University of Alaska, Fairbanks, Alaska 99775 USA 11United States Department of Agriculture Forest Service, Pacific Northwest Research Station, Alaska Wood Utilization Research and Development Center, 204 Siginaka Way, Sitka, Alaska 99835 USA 12Forest Health Protection, State and Private Forestry, United States Department of Agriculture Forest Service, Fairbanks Unit, 3700 Airport Way, Fairbanks, Alaska 99709 USA 13Department of Biology, University of Florida, 220 Bartram Hall, P.O. Box 118526, Gainesville, Florida 32611 USA 14Department of Forest Sciences, School of Natural Resources and Agricultural Sciences, University of Alaska, Fairbanks, Alaska 99775 USA Citation: Wolken, J. M., et al. 2011. Evidence and implications of recent and projected climate change in Alaska’s forest ecosystems. Ecosphere 2(11):124. doi:10.1890/ES11-00288.1 Abstract. The structure and function of Alaska’s forests have changed significantly in response to a changing climate, including alterations in species composition and climate feedbacks (e.g., carbon, radiation budgets) that have important regional societal consequences and human feedbacks to forest ecosystems. In this paper we present the first comprehensive synthesis of climate-change impacts on all forested ecosystems of Alaska, highlighting changes in the most critical biophysical factors of each region. We developed a conceptual framework describing climate drivers, biophysical factors and types of change to illustrate how the biophysical and social subsystems of Alaskan forests interact and respond directly and indirectly to a changing climate. We then identify the regional and global implications to the climate system and associated socio-economic impacts, as presented in the current literature. Projections of temperature and precipitation suggest wildfire will continue to be the dominant biophysical factor in the Interior-boreal forest, leading to shifts from conifer- to deciduous-dominated forests. Based on existing research, projected increases in temperature in the Southcentral- and Kenai-boreal forests will likely increase the frequency and severity of insect outbreaks and associated wildfires, and increase the probability of establishment by invasive plant species. In the Coastal-temperate forest region snow and ice is regarded as the dominant biophysical factor. With continued warming, hydrologic changes related to more rapidly melting glaciers and rising elevation of the winter snowline will alter discharge in many rivers, which will have important v www.esajournals.org 1 November 2011 v Volume 2(11) v Article 124 WOLKEN ET AL. consequences for terrestrial and marine ecosystem productivity. These climate-related changes will affect plant species distribution and wildlife habitat, which have regional societal consequences, and trace-gas emissions and radiation budgets, which are globally important. Our conceptual framework facilitates assessment of current and future consequences of a changing climate, emphasizes regional differences in biophysical factors, and points to linkages that may exist but that currently lack supporting research. The framework also serves as a visual tool for resource managers and policy makers to develop regional and global management strategies and to inform policies related to climate mitigation and adaptation. Key words: Alaska; boreal forest; climate change; climate projections; coastal-temperate forest; conceptual framework; disturbance regime; ecosystem services; insects and disease; invasive species; permafrost; wildfire. Received 11 October 2011; accepted 13 October 2011; published 21 November 2011. Corresponding Editor: D. P. C. Peters. Copyright: Ó 2011 Wolken et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits restricted use, distribution, and reproduction in any medium, provided the original author and sources are credited. E-mail: [email protected] INTRODUCTION and globally. Ninety percent of the forests are classified as boreal (42 million ha), collectively Currently, climate changes are significantly representing 4% of the world’s boreal forests impacting Alaska’s ecosystems (ACIA 2005). (Shvidenko and Apps 2006); these occur These impacts have been repeatedly synthesized throughout the Interior-, Southcentral- and Ke- for arctic tundra (ACIA 2005, Hinzman et al. nai-boreal regions (Fig. 1B). Coastal-temperate 2005, McGuire et al. 2009) and portions of the forests (5 million ha) comprise 10% of Alaska’s boreal forest (Chapin et al. 2006a), but there has forests and represent 19% of the world’s coastal- been no comprehensive review of climate-change temperate forests (NAST 2003). Forests in Alaska impacts on the broad spectrum of Alaskan play a large role in the economies and livelihoods forests, which is the goal of this review. Changes of people, as a result of their proximity to urban in high-latitude forests have important implica- and rural communities, and a diversity of tions both regionally and globally. Shifts in the associated ecosystem services (MEA 2005). disturbance regimes of Alaska’s forests (boreal Changes in forest structure and function will and coastal-temperate rainforest biomes) at the not only directly impact the biological compo- regional scale directly affect the global climate nents of these ecosystems, but will also have system through greenhouse gas emissions (Tan et important consequences for society (Flint 2006, al. 2007) and altered surface-energy budgets Chapin et al. 2008, Trainor et al. 2009). (Chapin et al. 2000, Randerson et al. 2006). Changes in boreal forests have the potential to Climate-related changes in Alaskan forests also affect the global climate system for several have important regional societal consequences, reasons. First, the boreal biome comprises one- and human responses to these changes may third of the Earth’s total forested area (Shvidenko amplify their impact on forest ecosystems. and Apps 2006) and is one of the biomes Understanding the current and potential future expected to change most rapidly with future impacts of contemporary climate change is climate change (Christensen et al. 2007). Second, important not only for regional-level adaptive boreal ecosystems contain 40% of the earth’s management, but also for national and interna- reactive soil organic carbon (McGuire et al. 1995). tional decision- and policy-making related to Third, the age-dependent stand structures and mitigation and adaptation strategies. species compositions characteristic of boreal Alaska’s forests (Fig. 1A) cover one-third of the forests modulate high-latitude energy budgets state’s 172 million ha of land (Parson et al. 2001) by affecting surface albedo (Euskirchen et al. and are functionally significant, both regionally 2009a). And fourth, carbon cycling, albedo, and v www.esajournals.org 2 November 2011 v Volume 2(11) v Article 124 WOLKEN ET AL. Fig. 1. Alaska maps illustrating (A) total forested area, (B) forest region boundaries of the: (1) Interior-boreal forest that is bounded by the Brooks Range to the north, the Alaska Range to the south, and the Seward Peninsula to the west; (2) Southcentral-boreal forest that includes the forests south of the Alaska Range, west of the Alaska- Yukon border, and east of the Alaska Peninsula; (3) Kenai-boreal forest that includes the western side of the Kenai Peninsula; and (4) Coastal-temperate forest that occurs on the Alaska Panhandle, the eastern portion of the Kenai Peninsula, Prince William Sound, and the islands of the Kodiak archipelago, (C) average annual temperature from 1950–2008, and (D) length of growing season from 1950–2008. Length of growing