Breen
Amy L.
Breen
Amy L.
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ArticleShallow soils are warmer under trees and tall shrubs across arctic and boreal ecosystems(IOP Publishing, 2020-12-18) Kropp, Heather ; Loranty, Michael M. ; Natali, Susan M. ; Kholodov, Alexander L. ; Rocha, Adrian V. ; Myers-Smith, Isla H. ; Abbott, Benjamin W. ; Abermann, Jakob ; Blanc-Betes, Elena ; Blok, Daan ; Blume-Werry, Gesche ; Boike, Julia ; Breen, Amy L. ; Cahoon, Sean M. P. ; Christiansen, Casper T. ; Douglas, Thomas A. ; Epstein, Howard E. ; Frost, Gerald V. ; Goeckede, Mathias ; Høye, Toke T. ; Mamet, Steven D. ; O’Donnell, Jonathan A. ; Olefeldt, David ; Phoenix, Gareth K. ; Salmon, Verity G. ; Sannel, A. Britta K. ; Smith, Sharon L. ; Sonnentag, Oliver ; Smith Vaughn, Lydia ; Williams, Mathew ; Elberling, Bo ; Gough, Laura ; Hjort, Jan ; Lafleur, Peter M. ; Euskirchen, Eugenie ; Heijmans, Monique M. P. D. ; Humphreys, Elyn ; Iwata, Hiroki ; Jones, Benjamin M. ; Jorgenson, M. Torre ; Grünberg, Inge ; Kim, Yongwon ; Laundre, James A. ; Mauritz, Marguerite ; Michelsen, Anders ; Schaepman-Strub, Gabriela ; Tape, Ken D. ; Ueyama, Masahito ; Lee, Bang-Yong ; Langley, Kirsty ; Lund, MagnusSoils are warming as air temperatures rise across the Arctic and Boreal region concurrent with the expansion of tall-statured shrubs and trees in the tundra. Changes in vegetation structure and function are expected to alter soil thermal regimes, thereby modifying climate feedbacks related to permafrost thaw and carbon cycling. However, current understanding of vegetation impacts on soil temperature is limited to local or regional scales and lacks the generality necessary to predict soil warming and permafrost stability on a pan-Arctic scale. Here we synthesize shallow soil and air temperature observations with broad spatial and temporal coverage collected across 106 sites representing nine different vegetation types in the permafrost region. We showed ecosystems with tall-statured shrubs and trees (>40 cm) have warmer shallow soils than those with short-statured tundra vegetation when normalized to a constant air temperature. In tree and tall shrub vegetation types, cooler temperatures in the warm season do not lead to cooler mean annual soil temperature indicating that ground thermal regimes in the cold-season rather than the warm-season are most critical for predicting soil warming in ecosystems underlain by permafrost. Our results suggest that the expansion of tall shrubs and trees into tundra regions can amplify shallow soil warming, and could increase the potential for increased seasonal thaw depth and increase soil carbon cycling rates and lead to increased carbon dioxide loss and further permafrost thaw.
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ArticleBiomass offsets little or none of permafrost carbon release from soils, streams, and wildfire : an expert assessment(IOPScience, 2016-03-07) Abbott, Benjamin W. ; Jones, Jeremy B. ; Schuur, Edward A. G. ; Chapin, F. Stuart ; Bowden, William B. ; Bret-Harte, M. Syndonia ; Epstein, Howard E. ; Flannigan, Michael ; Harms, Tamara K. ; Hollingsworth, Teresa N. ; Mack, Michelle C. ; McGuire, A. David ; Natali, Susan M. ; Rocha, Adrian V. ; Tank, Suzanne E. ; Turetsky, Merritt R. ; Vonk, Jorien E. ; Wickland, Kimberly ; Aiken, George R. ; Alexander, Heather D. ; Amon, Rainer M. W. ; Benscoter, Brian ; Bergeron, Yves ; Bishop, Kevin ; Blarquez, Olivier ; Bond-Lamberty, Benjamin ; Breen, Amy L. ; Buffam, Ishi ; Cai, Yihua ; Carcaillet, Christopher ; Carey, Sean K. ; Chen, Jing M. ; Chen, Han Y. H. ; Christensen, Torben R. ; Cooper, Lee W. ; Cornelissen, Johannes H. C. ; de Groot, William J. ; DeLuca, Thomas Henry ; Dorrepaal, Ellen ; Fetcher, Ned ; Finlay, Jacques C. ; Forbes, Bruce C. ; French, Nancy H. F. ; Gauthier, Sylvie ; Girardin, Martin ; Goetz, Scott J. ; Goldammer, Johann G. ; Gough, Laura ; Grogan, Paul ; Guo, Laodong ; Higuera, Philip E. ; Hinzman, Larry ; Hu, Feng Sheng ; Hugelius, Gustaf ; JAFAROV, ELCHIN ; Jandt, Randi ; Johnstone, Jill F. ; Karlsson, Jan ; Kasischke, Eric S. ; Kattner, Gerhard ; Kelly, Ryan ; Keuper, Frida ; Kling, George W. ; Kortelainen, Pirkko ; Kouki, Jari ; Kuhry, Peter ; Laudon, Hjalmar ; Laurion, Isabelle ; Macdonald, Robie W. ; Mann, Paul J. ; Martikainen, Pertti ; McClelland, James W. ; Molau, Ulf ; Oberbauer, Steven F. ; Olefeldt, David ; Paré, David ; Parisien, Marc-André ; Payette, Serge ; Peng, Changhui ; Pokrovsky, Oleg ; Rastetter, Edward B. ; Raymond, Peter A. ; Raynolds, Martha K. ; Rein, Guillermo ; Reynolds, James F. ; Robards, Martin ; Rogers, Brendan ; Schädel, Christina ; Schaefer, Kevin ; Schmidt, Inger K. ; Shvidenko, Anatoly ; Sky, Jasper ; Spencer, Robert G. M. ; Starr, Gregory ; Striegl, Robert ; Teisserenc, Roman ; Tranvik, Lars J. ; Virtanen, Tarmo ; Welker, Jeffrey M. ; Zimov, Sergey A.As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%–85% of permafrost carbon release can still be avoided if human emissions are actively reduced.
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ArticleThe footprint of Alaskan tundra fires during the past half-century : implications for surface properties and radiative forcing(IOP Publishing, 2012-12-19) Rocha, Adrian V. ; Loranty, Michael M. ; Higuera, Philip E. ; Mack, Michelle C. ; Hu, Feng Sheng ; Jones, Benjamin M. ; Breen, Amy L. ; Rastetter, Edward B. ; Goetz, Scott J. ; Shaver, Gaius R.Recent large and frequent fires above the Alaskan arctic circle have forced a reassessment of the ecological and climatological importance of fire in arctic tundra ecosystems. Here we provide a general overview of the occurrence, distribution, and ecological and climate implications of Alaskan tundra fires over the past half-century using spatially explicit climate, fire, vegetation and remote sensing datasets for Alaska. Our analyses highlight the importance of vegetation biomass and environmental conditions in regulating tundra burning, and demonstrate that most tundra ecosystems are susceptible to burn, providing the environmental conditions are right. Over the past two decades, fire perimeters above the arctic circle have increased in size and importance, especially on the North Slope, indicating that future wildfire projections should account for fire regime changes in these regions. Remote sensing data and a literature review of thaw depths indicate that tundra fires have both positive and negative implications for climatic feedbacks including a decadal increase in albedo radiative forcing immediately after a fire, a stimulation of surface greenness and a persistent long-term (>10 year) increase in thaw depth. In order to address the future impact of tundra fires on climate, a better understanding of the control of tundra fire occurrence as well as the long-term impacts on ecosystem carbon cycling will be required.