A new University of Alberta study shows that forests of spruce trees and shrubs in parts of northern Canada are taking over what were once tundra landscapes because of global warming and evicting and endangering species that live there quicker than scientists thought.
Tundra is land area where tree growth is inhibited by low temperatures and a short growing season. The Arctic tundra is underlain by permafrost and is usually saturated.
The boundary, or treeline, between forest and tundra ecosystems is a prominent landscape feature in both Arctic and mountain environments. As global temperatures continue to increase, the treeline is expected to advance - but the new research shows that this shift can surge ahead.
"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 Dr. Ryan Danby, from the U of A Department of Biological Sciences. "But our data indicates that there was an upslope surge of trees in response to warmer temperatures. It's like it waited until conditions were just right and then it decided to get up and run, not just walk."
Researchers reconstructed a 300-year history of tree density and treeline position by looking at tree rings. They found that a rapid change in response to climate warming during the early mid 20th century was observed at all locations. Treelines advanced considerably - as much as 85 metres elevation - on warm, south-facing slopes and tree density increased as much as 65 per cent on cooler, north-facing slopes.
"The mechanism of change appears to be associated with occasional years of extraordinarily high seed production, triggered by hot, dry summers, followed by successive years of warm temperatures favourable for seedling growth and survival," said Danby.
Widespread changes to treelines could have significant impacts, says Danby. As tundra habitats are lost and fragmented, species and habitats are forced to move upwards as well. "The problem is that in mountainous areas you can only go so high so they get forced into smaller and smaller areas," said Danby.
"These results are very relevant to the current debate surrounding climate change because they provide real evidence that vegetation change will be quite considerable in response to future warming, potentially transforming tundra landscapes into open spruce woodlands," said Danby, who will be participating in an International Polar Year project that will be examining treeline dynamics across the circumpolar north.
Source : University of Alberta
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