This most commonly occurs in northern subarctic taiga forests of Black Spruce (Picea mariana) under which discontinuous permafrost or ice wedges have melted, causing trees to tilt at various angles.
Tilted trees may also be caused by frost heaving, and subsequent palsa development, hummocks, earthflows, forested active rock glaciers, landslides, or earthquakes. In stands of spruce trees of equal age that germinated in the permafrost active layer after a fire, tilting begins when the trees are 50 to 100 years old, suggesting that surface heaving from new permafrost aggradation can also create drunken forests.
Permafrost, which is soil (or rock) that remains below 0 °C for at least two consecutive years, forms a solid matrix in soil which can extend to a depth of hundreds of meters. The permafrost prevents trees from developing deep root systems; for example, the Black Spruce that has adapted to permafrost soils has no significant taproot. In areas where the permafrost temperature is near the melting point of water, climate variations, or loss of surface vegetation from fire, flooding, construction, or deforestation, can thaw the upper extents of the permafrost, creating a thermokarst, the scientific name for a ground slump caused by melting permafrost. The thermokarst undermines the shallow root bed of these trees, causing them to lean or fall. Thermokarst lakes are surrounded by a ring of drunken trees leaning toward the lake, which makes these land features easily identifiable.
Drunken trees may eventually die from their displacement, and in ice-rich permafrost, the entire drunken forest ecosystem can be destroyed by melting. Tilted trees that do not topple over may recover by using gravitropism to resume vertical growth, thereby taking on a curved shape. The reaction wood formed by this process can be studied using dendrochronology using annual growth rings to determine when the tree was subjected to tilting.
Relationship to climate change
Drunken trees are not a completely new phenomenon—dendrochronological evidence can date thermokarst tilting back to at least the 19th century. The southern extent of the subarctic permafrost reached a peak during the Little Ice Age of the 16th and 17th centuries, and has been in decline since then.
Permafrost is typically in disequilibrium with climate, and much of the permafrost that remains is in a relict state. However, the rate of thawing has been increasing, and a great deal of the remaining permafrost is expected to thaw during the 21st century.
Al Gore cited drunken trees caused by melting permafrost in Alaska as evidence of global warming, as part of his presentation in the 2006 documentary film An Inconvenient Truth. Similar warming leading to permafrost thawing in neighboring Siberia has been attributed to a combination of anthropogenic climate change, a cyclical atmospheric phenomenon known as the Arctic oscillation, and feedbacks due to albedo changes after melting ice exposes bare ground and ocean which absorb, rather than reflect, solar radiation.
- Nikiforoff, C. (1928). "The perpetually frozen subsoil of Siberia". Soil Sci. 26: 61–79.
- Stevens, William K. (1998-08-18). "Dead Trees and Shriveling Glaciers as Alaska Melts". The New York Times. Retrieved 2007-12-19. "Here and there, roadside utility poles destabilized by the melting tilt at crazy angles. So do trees, creating a phenomenon known as drunken forest."
- de Villiers, Marq (2001). Water: The Fate of Our Most Precious Resource. Boston: Mariner Books. ISBN 0-618-12744-5. "…caused what the locals call "drunken forests," the trees tilting and leaning…"
- Kolbert, Elizabeth (2005). "The Climate Of Man—ii" (PDF). New Yorker. Retrieved 2007-12-17. "Romanovsky pointed out a long trench running into the woods. The trench, he explained, had been formed when a wedge of underground ice had melted. The spruce trees that had been growing next to it, or perhaps on top of it, were now listing at odd angles, as if in a gale. Locally, such trees are called “drunken.”"
- Kokelj, S.V.; Burn, C.R. (2003). "Tilt of Spruce Trees near Ice Wedges, Mackenzie Delta, Northwest Territories, Canada". In Phillips, Marcia; Springman, Sarah M.; Arenson, Lukas U. Permafrost—Proc. 8th Int Conf. Permafrost. Rotterdam: A.A. Balkema. pp. 567–570. ISBN 90-5809-582-7. "This observation suggests that aggradational ice development associated with post-fire active-layer thinning causes the overlying ground to heave … forests with tilted trees were underlain by permafrost of high ice content and forests with straight trees were underlain by ice-poor permafrost."
- Ranson, Jon (2007-08-01). "Science Blog - Expedition to Siberia". Siberia Blog. NASA Earth Observatory. Retrieved 2007-12-19. "Permafrost that has not melted provides a solid foundation that holds trees upright. When permafrost melts, as it has here, the layer of loose soil deepens and trees lose their foundations, tipping over at odd angles."
- Crum, Howard Alvin (1988). A Focus on Peatlands and Peat Mosses (Great Lakes Environment). University of Michigan. p. 278. ISBN 0-472-06378-2. "drunken forest A stand of black spruce in subarctic regions of discontinuous permafrost … where the ice core melts causing trees to lean or fall"
- Pielou, E.C. (1991). After the Ice Age: the return of life to glaciated North America. Chicago, Illinois: University of Chicago Press. p. 84. ISBN 0-226-66812-6. "The occasional groups of stunted trees that do manage to establish themselves often form a "drunken forest"; their trunks lean in all directions because frost-heaving takes place and the rising mounds of freezing soil tilt the trees growing on them."
- Scott, Peter A.; Hansell, Roger I.C.; Erickson, William R. (1993). "Influences of wind and snow on northern tree-line environments at Churchill, Manitoba, Canada" (PDF). Arctic 46 (4): 316–323. Retrieved 2007-12-19. "Such trees develop in association with frost heaving and subsequent palsa development, resulting in “drunken forests”"
- Zoltai, S.C. (1975). "Tree Ring Record of Soil Movements on Permafrost". Arctic and Alpine Research (INSTAAR, University of Colorado) 7 (4): 331–340. doi:10.2307/1550177. JSTOR 1550177. "Trees growing on hummocky permafrost terrain are subject to periodic tilting, and this tilting is recorded as compression wood."
- ""Drunken Forest" in Colorado". Incorporated Research Institutions for Seismology. Retrieved 2007-12-16. "Photo showing tilted trees in the "drunken forest". The trees grow atop the Slumgullion earthflow, which is four miles long and 2000 feet wide, near Lake City, CO."
- Wicander, Reed; Monroe, James S. (2004). Physical Geology : Exploring the Earth (with PhysicalGeologyNow and InfoTrac). Pacific Grove: Brooks Cole. p. 419. ISBN 0-534-39987-8. "Slow mass movements advance at an imperceptible mate and are usually detectable only by the effects of their movement, such as tilted trees and power poles…"
- van Everdingen, Robert (ed. 1998 revised May 2005). "drunken forest". Multi-language glossary of permafrost and related ground-ice terms. Boulder, Colorado: National Snow and Ice Data Center/World Data Center for Glaciology. "Active, forested rock glaciers may also exhibit this phenomenon due to differential movements."
- Rozell, Ned (1995-09-21). "Formerly Frosty Footing Causes Drunken Forests, Alaska Science Forum". Geophysical Institute, University of Alaska Fairbanks. Retrieved 2007-12-16. "Melting permafrost is the most common cause of the drunken forest.… Landslides and earthquakes also can create drunken forests,…"
- "Permafrost Landscapes" (PDF). Denali National Park and Preserve. National Park Service. Retrieved 2007-12-16. "Permafrost is soil or rock that remains below 0°C for at least two consecutive years.… Spruce trees leaning in different directions (known as “drunken forest”) can be a clue to frost heaving or melting of permafrost beneath."
- Scoggins, Dow (2004). Discovering Denali: A Complete Reference Guide to Denali National Park and Mount McKinley, Alaska. iUniverse Star. pp. 64–65. ISBN 0-595-29737-4. "…the soil is freed and sinks into spaces left by the retreating liquid. Thus, the ground often slumps beneath the trees, causing them to lean drunkenly."
- Pitcher, Don (2007). Moon Alaska (Moon Handbooks). Avalon Travel Publishing. p. 357. ISBN 1-56691-929-0. "As an adaptation to the permafrost, these spruce trees have evolved a root system that spreads horizontally across the surface soil; there's no tap root to speak of."
- Fitzpatrick, E.A. (1997). "I. Arctic soils and permafrost". In Marquiss, Mick; Woodin, Sarah J. Ecology of Arctic Environments: 13th Special Symposium of the British Ecological Society. Symposia of the British Ecological Society. Cambridge, England, United Kingdom: Cambridge University Press. p. 20. ISBN 0-521-83998-X. "It can form naturally by a change in an environmental factor such as an increase in temperature, or the death of the vegetation following a fire or flooding. Often in the forested tundra, thermokarst is induced by humans due to deforestation."
- Sater, John E. (1969). The Arctic Basin. Arctic Institute of North America. p. 102. "A thermokarst lake often has a distinctive border of "drunken trees", and may thus be identified readily."
- Vitt, H.D.; Halsey, L.A.; Zoltai, S.C. (2000). "The changing landscape of Canada’s western boreal forest: the current dynamics of permafrost" (PDF). Can. J. For. Res 30 (2): 283–287. doi:10.1139/cjfr-30-2-283. Retrieved 2007-12-17. "As permafrost is in disequilibrium with climate, much of the permafrost that remains is in a relict state.… As the permafrost surface subsides, trees die and are tilted resulting in the development of “drunken forests” and the formation of compression wood…"
- Osterkamp, T.E.; Viereck, L.; Shur, Y.; Jorgenson, M.T.; Racine, C.; Doyle, A.; Boone, R.D. (2000). "Observations of Thermokarst and Its Impact on Boreal Forests in Alaska, USA". Arctic, Antarctic, and Alpine Research (INSTAAR, University of Colorado) 32 (3): 303–315. doi:10.2307/1552529. JSTOR 1552529. "At sites generally underlain by ice-rich permafrost, forest ecosystems can be completely destroyed.… Tipped trees at the edge of thermokarst can be used to age the time of thawing of the underlying permafrost…"
- Alman, Josh. "Drunken Trees - OISE-UTS - ENCORE" (wiki). Canadian biodiversity concerns. University of Toronto Schools. Retrieved 2007-12-16. "Some drunken trees recover by using gravitropism to re-orient themselves upwards; others simply topple sideways and die."
- Huisman, L.M. (2002). "Development of Compression Wood in Trees of the Drunken Forest, Central Yukon Territory". Unpublished MA thesis (Carleton University, Ottawa). "Ninety-two cross-sectional discs were extracted from tilted trees growing in hummocky and non-hummocky permafrost terrain near Mayo, Yukon Territory, in order to investigate the development of compression wood between 1900 and 2000."
- "Dendrochronology - the study of tree rings". Activities. GLOBE Canada. Retrieved 2007-12-18. "Trees on the edge of a patch of degrading permafrost … will all exhibit reaction wood starting as soon as the event happens or in the following spring, if the tilting happened in the winter."
- Perkins, Sid (2007-03-10). "Not-So-Perma Frost". Science News. Archived from the original on 2007-10-16. Retrieved 2007-12-16. "When the centuries-long cold spell called the Little Ice Age ended about 150 years ago, glaciers and permafrost reached their maximum extent of the past few millennia."
- Halsey, L.A.; Vitt, D.H.; Zoltai, S.C. (1995). "Disequilibrium response of permafrost in boreal continental western Canada to climate change" (PDF). Climatic Change 30 (1): 57–73. doi:10.1007/BF01093225. Retrieved 2007-12-19. "In the midboreal zone, internal lawns are present in bogs and in fens. These internal lawns do not presently contain permafrost but did in the recent past, representing degradation of permafrost since the Little Ice Age."
- Jorgenson, M.T.; Racine, C.H.; Walters, J.C.; Osterkamp, T.E. (2001). "Permafrost Degradation and Ecological Changes Associated with a Warming Climate in Central Alaska" (PDF). Climatic Change 48 (4): 551–579. doi:10.1023/A:1005667424292. Retrieved 2007-12-19. "Evidence indicates this permafrost degradation began in the mid-1700s and is associated with periods of relatively warm climate during the mid-late 1700s and 1900s."
- "Permafrost - Permafrost and Climate Change". Geological Survey of Canada. Natural Resources Canada. 2006-06-15. Retrieved 2007-12-18. "…permafrost … is in disequilibrium with the present climate and has been slowly disappearing in response to climate warming since the Little Ice Age.… Much of the area of discontinuous permafrost is already in disequilibrium with the current climate and is still responding to changes of the last century."
- "Climate Change And Permafrost Thaw Alter Greenhouse Gas Emissions In Northern Wetlands". TerraDaily. 2007-08-12. Retrieved 2007-12-19. "But rising atmospheric temperatures are accelerating rates of permafrost thaw in northern regions, says MSU researcher Merritt Turetsky."
- Payette, S.; Delwaide, A.; Caccianiga, M.; Beauchemin, M. (2004). "Accelerated thawing of subarctic peatland permafrost over the last 50 years". Geophysical Research Letters 31 (18): L18208. Bibcode:2004GeoRL..3118208P. doi:10.1029/2004GL020358. "Rapid permafrost melting over the last 50 years caused the concurrent formation of thermokarst ponds and fen-bog vegetation with rapid peat accumulation through natural successional processes of terrestrialization."
- "Earth's permafrost starts to squelch". BBC News. 2004-12-29. Retrieved 2007-12-18. "Boreholes in Svalbard, Norway, for example, indicate that ground temperatures rose 0.4C over the past decade, four times faster than they did in the previous century, according to Charles Harris, a geologist at the University of Cardiff, UK, and a coordinator of Permafrost and Climate in Europe (Pace), which is contributing data to the GTNP."
- Camill, P. (2005). "Permafrost Thaw Accelerates in Boreal Peatlands During Late-20th Century Climate Warming" (PDF). Climatic Change 68 (1): 135–152. doi:10.1007/s10584-005-4785-y. Retrieved 2007-12-19. "Permafrost thaw in central Canadian peatlands has accelerated significantly since 1950,… This magnitude of warming will begin to eliminate most of the present range of sporadic and discontinuous permafrost in central Canada by 2100."
- Lawrence, D.M.; Slater, A.G. (2005). "A projection of severe near-surface permafrost degradation during the 21st century" (PDF). Geophys. Res. Lett 32 (24): L244010. Bibcode:2005GeoRL..3224401L. doi:10.1029/2005GL025080. Retrieved 2007-12-21. "CCSM3 projections show dramatic permafrost degradation by 2100 under both high and low greenhouse gas emission scenarios."
- "Siberia's rapid thaw causes alarm". BBC News. 2005-08-11. Retrieved 2007-12-18. "The warming is believed to be due to a combination of man-made climate change, a cyclical atmospheric phenomenon known as the Arctic oscillation and feedbacks caused by melting ice"
- Pearce, Fred (2005-08-11). "Climate warning as Siberia melts". New Scientist. Retrieved 2007-12-19. "Western Siberia has warmed faster than almost anywhere else on the planet, with an increase in average temperatures of some 3°C in the last 40 years.… Similar warming has also been taking place in Alaska:…"
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