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According to scientists, melting ground is to blame for tilting spruce trees.


Drunken Trees: Dramatic Signs of Climate Change

As the permafrost melts in the north, forests no longer grow straight.

Sarah James, an Alaska Native elder, says global warming is radically changing her homeland. Even the forests no longer grow straight. Melting ground has caused trees to tilt or fall.

"Because permafrost melts, it causes a lot of erosion," says James, who lives in Arctic Village, a small Native American village in northeastern Alaska. "A lot of trees can't stand up straight. If the erosion gets worse, everything goes with it."

Permafrost is permanently frozen ground. But climate change has caused much of that ground to melt at an unprecedented rate. The ground buckles and sinks, causing trees to list at extreme angles.

Sometimes the trees survive the stress and continue growing, uprighting themselves to vertical. Other times they collapse or drown from rising water tables as subterranean ice melts. Because such trees seem to stagger across the landscape, people often call them "drunken trees."

Although trees can lean or curve for a number of reasons, including disturbance of soil caused by man-made excavations or landslides, the melting permafrost is making leaning trees more prevalent.

It's not just trees. Slumping land caused by melting permafrost also cracks pavement, breaks pipelines, and opens holes, causing expensive damage to houses and roads. "We have whole families who have had to move because their houses are not safe anymore," says James.

Wildlife has been affected by the shifting landscape as well. James has seen declines in spawning fish, nesting birds, and small mammals.

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Fallen trees after the permafrost melted in Fairbanks, Alaska, in 2004.

The Science of Drunken Trees

Torre Jorgenson, a scientist in Fairbanks, Alaska, who studies permafrost, says melting of ice crystals below the ground can cause slumps as large as 10 meters (33 feet). That can "swallow a whole house," says Jorgensen, who heads Alaska Ecoscience, which does research for government agencies.

Drunken trees are becoming most prevalent in lowland arboreal forests across Alaska, Canada, and northern Eurasia, says Jorgenson. On steeper slopes, meltwater usually runs downhill quickly, which causes less disturbance on the surface. Birch and black spruce—with their shallow root systems—are the species most likely to lean.

Some climate models have predicted that most permafrost could melt by the end of the century. Jorgenson thinks it will take longer, since soil layers above the frozen ground are good insulators. But the area north of Fairbanks is predicted to warm by four to six degrees Celsius by the end of the century.

"In the last hundred years we've increased about 1.5 degrees Celsius, so that's going to be a huge sledgehammer coming down," says Jorgenson.

In that case, there are likely to be more drunken trees. Right now, around 7 to 8 percent of the land in the middle boreal zone in Alaska is showing some signs of drunken trees or other melting-related impacts, says Jorgenson.

With the impacts hitting home, the road that winds near his house has to be rebuilt every few years because of damage caused by slumping. This year, engineers are adding insulation to try to reduce the impact of the melting, but that's expensive. (See "World Not Ready for Climate Change.")

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This boreal pond formed after the permafrost melted in the Alaska Range.

What's a "Thermokarst"?

Drunken, or "collapsed" trees, are one of the more visible signs of change in the north. Ground that collapses as a result of melting permafrost has a technical name: thermokarst. (Thermo means heat, and karst refers to collapse.)

In addition to collapsed trees, slumping land often leads to the formation of new thermokarst lakes, if enough meltwater collects in a depression. In that case, drunken trees are often found ringing the water.

"The melting permafrost as a process in the region is very, very serious," says Tero Mustonen, who leads the Snowchange Cooperative, a nonprofit organization in Finland. A warming north has "profound consequences for both the global system and the local human societies," he says, adding that the release of methane, a potent greenhouse gas, from thawed ground is a particular worry.

Other impacts include disruption to reindeer migrations, changes in river courses, and stress on fisheries. (See "7 Species Hit Hard by Climate Change.")

Downstream Effects

On the upside, drunken trees could benefit some Native communities, says Jon Rosales, a professor of environmental studies at St. Lawrence University in Canton, New York. More downed trees could mean more driftwood—an important source of fuel and building material for these communities—flowing into rivers and toward the coast.

"Climate change, global warming, is real here in the Arctic," Sarah James, the elder, concludes. "It seems like when I go other places they're not worried about it, but one way or another it's going to get there."

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