BEIJING, March 12 (Xinhuanet) -- Forests of spruce
trees are invading the Arctic tundra because of global warming and evicting and
endangering species that live there quicker than scientists thought, a new study
was quoted as saying Monday by news reports.
Tundra is land area where tree growth is inhibited by
low temperatures and a short growing season. In the Arctic, the tundra is
dominated by permafrost, a layer of permanently frozen subsoil.
Lichens, grasses and mosses are the only
vegetation that can grow in such frigid conditions. Forests of spruce trees and
shrubs neighbor these tundra areas, and the boundary where they meet is called
The permafrost thaws in summer and the tundra becomes
covered in bogs and lakes, offering a unique habitat for plants. But global
warming has lengthened the summer warming season and promoted tree growth,
causing the treeline to encroach on the tundra.
Researchers reconstructed a 300-year history of tree
density and treeline position by looking at tree rings. The results show trees
can invade the tundra faster than previously thought.
"The conventional thinking on treeline dynamics has
been that advances are very slow because conditions are so harsh at these high
latitudes and altitudes," said Ryan Danby of the University of Alberta. "But
what our data indicates is that there was an upslope surge of trees in response
to warmer temperatures. It's like it waited until conditions were right and then
it decided to get up and run, not just walk."
While in many places the idea of more trees is a good
one, this Arctic takeover endangers species like caribou and sheep that thrive
in the tundra, as well as the native people who depend on these species for
The details of the study are published in the March
issue of the Journal of Ecology. Danby plans to continue his research as a part
of the United Nation's International Polar Year research effort.