Scientists in the Alaskan Arctic have discovered that shrubs are growing larger and spreading across previously barren territory in the tundra. The findings add to the scientific consensus that the region is gradually getting warmer.
Federal researchers combed through archives of aerial photos, comparing new images to those of the same locations taken 50 years ago. Of the 66 aerial photos taken for the study, growth increases were reported in 36 of those images, with the growth of some plants estimated to be as much as 15 percent
In the remaining 30 images, no changes to tundra shrub cover -- either growth or reduction -- were found.
''The Alaskan Arctic for three decades has gotten considerably warmer and experimental and model studies have shown that there should be more shrubs,'' said study co-author Matthew Sturm, a geophysicist at US Army Cold Regions Research & Engineering Laboratory at Fort Wainwright, Alaska.
''We come along and find these photos, and that's exactly what we're seeing,'' Sturm said.
The Army lab team said the study is the first time that tundra growth has been analyzed in the high-latitude area through picture comparisons. The results appear in the latest issue of the journal Nature.
The findings echo other Alaskan Arctic studies performed with satellite imaging in the Alaskan Arctic, according to scientists who did not participate in the photo analysis.
''It certainly opens the door for more work to support the suggestion that temperature is increasing,'' said Jeff Hicke, a research associate at the University of Colorado at Boulder, who recently conducted a separate study on tundra vegetation growth using satellite imagery.
Aerial photos were taken in July of 1999 and 2000 from a low-flying aircraft over a swath of land measuring 248 miles from east-to-west and 93 miles north-south. The tundra parcel is located between the Brooks Range and the Arctic coast.
They identify the exact area, including the same shrub clusters, that the military originally photographed between 1948 and 1950.
Scientists said the new photographs clearly illustrate a shift in the treeline over the past 50 years. They also show moose footprints, indicating the animals have migrated northward to follow the shrubs.
''The treeline is definitely moving. You can see the increase,'' said co-author Ken Tape, a research technician at the University of Alaska Fairbanks Geophysical Institute. ''There's more spruce in this picture than in that picture. The treeline is moving north.''
The deciduous shrubs below the treeline were identified as dwarf birch, willow and green alder. The photos represented changes in height, diameter and density. The largest increase in shrubbery was 15 percent, Tape said.
The research area is virtually uninhabited. Because the tundra is frozen for as long as nine months during the intense Arctic winter and is spongy in the summer, the region is not prone to fires.
''There's virtually no human impact, which makes it a particularly good laboratory for studying these kinds of vegetative change,'' Tape said.
According to a study published in February by the United Nations, climate change in polar regions is expected to be among the most dramatic anywhere on Earth. Already, the extent and thickness of Arctic sea ice have decreased, permafrost has thawed and the distribution and abundance of many species has been effected.
A second U.N. climate summary released in January estimated that global temperatures could rise as much as 10.5 degrees over the next century.
The Army lab study also suggests the additional shrub growth will extract more carbon dioxide from a warming atmosphere, helping to moderate the effects of global warming in future.
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