Drunken trees, tilted trees, or a drunken forest, is a stand of trees displaced from their normal vertical alignment.
This most commonly occurs in northern subarctic taiga

Taiga

Taiga , also known as the boreal forest, is a biome characterized by coniferous forests.Taiga is the world's largest terrestrial biome. In North America it covers most of inland Canada and Alaska as well as parts of the extreme northern continental United States and is known as the Northwoods...

 forests of Black Spruce (Picea mariana) under which discontinuous permafrost

Permafrost

In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...

 or ice wedge

Ice wedge

An ice wedge is a crack in the ground formed by a narrow or thin piece of ice that measures up to 3-4 metres wide at ground level and extends downwards into the ground up to several metres. During the winter months, the water in the ground freezes and expands...

s have melted, causing trees to tilt at various angles.
Tilted trees may also be caused by frost heaving

Frost heaving

Frost heaving results from ice forming beneath the surface of soil during freezing conditions in the atmosphere. The ice grows in the direction of heat loss , starting at the freezing front or boundary in the soil...

, and subsequent palsa

Palsa

thumb|right|300px|A group of well developed palsas as seen from abovePalsas are low, often oval, frost heaves occurring in polar and subpolar climates, which contain permanently frozen ice lenses...

 development,hummock

Hummock

A hummock is a boss or rounded knoll of ice rising above the general level of an ice-field, making sledge travelling in the Arctic and Antarctic region extremely difficult and unpleasant....

s, earthflow

Earthflow

An earthflow is a downslope viscous flow of fine grained materials that have been saturated with water, and moves under the pull of gravity. They are an intermediate type of mass wasting that is between downhill creep and mudflow...

s,forested active rock glacier

Rock glacier

Rock glaciers are distinctive geomorphological landforms of angular rock debris frozen in interstitial ice which may extend outward and downslope from talus cones, glaciers or terminal moraines of glaciers. There are two types of rock glaciers: periglacial glaciers, or talus-derived glaciers, and...

s,
landslides, or earthquakes. In stands of spruce trees of equal age that germinated in the permafrost active later after a fire, tilting begins when the trees are 50 to 100 years old, suggesting that surface heaving from new permafrost aggradation

Aggradation

Aggradation is the term used in geology for the increase in land elevation due to the deposition of sediment. Aggradation occurs in areas in which the supply of sediment is greater than the amount of material that the system is able to transport...

 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

Taproot

A taproot is an enlarged, somewhat straight to tapering plant root that grows vertically downward. It forms a center from which other roots sprout laterally.Plants with taproots are difficult to transplant...

. In areas where the permafrost temperature is near the melting point

Melting point

The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

 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

Thermokarst

Thermokarst is a land surface characterised by very irregular surfaces of marshy hollows and small hummocks formed as ice-rich permafrost thaws, that occurs in Arctic areas, and on a smaller scale in mountainous areas such as the Himalayas and the Swiss Alps...

, 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

Gravitropism

Gravitropism is a turning or growth movement by a plant or fungus in response to gravity. Charles Darwin was one of the first to scientifically document that roots show positive gravitropism and stems show negative gravitropism. That is, roots grow in the direction of gravitational pull and stems...

 to resume vertical growth, thereby taking on a curved shape. The reaction wood

Reaction wood

Reaction wood forms when part of a woody plant is subjected to mechanical stress, and helps to bring parts of the plant into an optimal position. This stress may be the result of gravity, wind exposure, snow buildup, soil movement, etc. The reaction wood is not externally visible, although...

 formed by this process can be studied using dendrochronology

Dendrochronology

Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree-rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year...

 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

Permafrost

In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...

 reached a peak during the Little Ice Age

Little Ice Age

The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

 of the 16th and 17th centuries, and has been in decline since then.
Permafrost is typically in disequilibrium

Thermodynamic equilibrium

In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, radiative equilibrium, and chemical equilibrium. The word equilibrium means a state of balance...

 with climate, and much of the permafrost that remains is in a relict

Relict

A relict is a surviving remnant of a natural phenomenon.* In biology a relict is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas....

 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.

Nobel laureate and former Vice President of the United States

Vice President of the United States

The Vice President of the United States is the holder of a public office created by the United States Constitution. The Vice President, together with the President of the United States, is indirectly elected by the people, through the Electoral College, to a four-year term...

 Al Gore

Al Gore

Albert Arnold "Al" Gore, Jr. served as the 45th Vice President of the United States , under President Bill Clinton. He was the Democratic Party's nominee for President in the 2000 U.S. presidential election....

 cited drunken trees caused by melting permafrost in Alaska

Alaska

Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

 as evidence of global warming

Global warming

Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

, as part of his presentation in the Academy Award winning 2006 documentary film

Documentary film

Documentary films constitute a broad category of nonfictional motion pictures intended to document some aspect of reality, primarily for the purposes of instruction or maintaining a historical record...

 An Inconvenient Truth

An Inconvenient Truth

An Inconvenient Truth is a 2006 documentary film directed by Davis Guggenheim about former United States Vice President Al Gore's campaign to educate citizens about global warming via a comprehensive slide show that, by his own estimate, he has given more than a thousand times.Premiering at the...

, directed by Davis Guggenheim

Davis Guggenheim

Philip Davis Guggenheim is an Academy Award-winning American film director and producer. His credits as a producer and director include Training Day, The Shield, Alias, 24, NYPD Blue, ER, Deadwood, and Party of Five and the documentaries An Inconvenient Truth and Waiting for 'Superman...

; but global warming skeptic

Global warming controversy

Global warming controversy refers to a variety of disputes, significantly more pronounced in the popular media than in the scientific literature, regarding the nature, causes, and consequences of global warming...

 Marlo Lewis, senior fellow of the Competitive Enterprise Institute

Competitive Enterprise Institute

The Competitive Enterprise Institute is a non-profit think tank founded on March 9, 1984 in Washington, D.C. by lobbyist Fred L. Smith, Jr to advance economic liberty and fight over-regulation by big government...

, claims that, "drunken trees may partly be a consequence of the PDO shift," referring to the 1976 switch to the warm phase of the Pacific decadal oscillation

Pacific decadal oscillation

The Pacific Decadal Oscillation is a pattern of Pacific climate variability that shifts phases on at least inter-decadal time scale, usually about 20 to 30 years. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20° N...

.
Similar warming leading to permafrost thawing in neighboring Siberia

Siberia

Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...

 has been attributed to a combination of anthropogenic climate change, a cyclical atmospheric phenomenon known as the Arctic oscillation

Arctic oscillation

The Arctic oscillation or Northern Annular Mode/Northern Hemisphere Annular Mode is an index of the dominant pattern of non-seasonal sea-level pressure variations north of 20N latitude, and it is characterized by pressure anomalies of one sign in the Arctic with the opposite anomalies centered...

, and feedbacks due to albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 changes after melting ice exposes bare ground and ocean which absorb, rather than reflect, solar radiation.

External links

• Tilted trees, edge of thermokarst lake, Yukon image at Iowa Digital Library
• Word Spy citations