Canada Tundra Turning Green

Canada Tundra Turning Green



March 2007 - Northern Canada's 
tundra is disappearing at a rapid rate, with forests of spruce 
trees and shrubs taking over the once frozen landscape, new 
research finds. The study offers further evidence of climate 
change and the authors warn it shows that the shift in the 
Canadian tundra can happen at a much faster speed than 
scientists originally thought. 
The research examines changes in the treeline between forest 
and tundra ecosystems, a prominent landscape feature in both 
Arctic and mountain environments. 
Scientists have long believed that the treeline will advance 
as global temperatures continue to increase, but the new study 
shows that such a shift will not always occur gradually. 
"The conventional thinking on treeline dynamics has been that 
advances are very slow because conditions are so harsh at 
these high latitudes and altitudes," explained study author 
Ryan Danby, a biologist with 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 just right and then it decided to get up 
and run, not just walk." 
Coniferous trees are invading the tundra, a consequence of the 
changing climate. 
The study, published in the "Journal of Ecology," analyzes 
reconstructed changes in the density and altitude of treeline 
forests in southwestern Yukon over the past three centuries. 
The research team used tree rings to date the year of 
establishment and death of spruce trees and reconstruct 
changes in treeline vegetation. They found that a rapid change 
in response to climate warming during the early mid 20th 
century was observed at all locations. 
On warm, south-facing slopes the treeline advanced as much as 
278 feet in elevation. Tree density increased as much as 65 
percent 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 favorable for seedling growth and 
survival," said Danby. 
Danby noted that there is also the concern about a "positive 
feedback" effect, which has been associated with the decrease 
in the Arctic ice cap. As the treeline advances, he explained, 
the reflectance of the land surface declines because 
coniferous trees absorb more sunlight than the tundra 
This light energy is then re-emitted to the atmosphere as 
heat, adding to warming and further fueling the advance of the 
treeline. 
"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, a participant in an 
International Polar Year project that will be examining 
treeline dynamics across the circumpolar north. 
Danby added that the shift will have adverse impacts on tundra 
species such as caribou and wild sheep, which will also be 
forced upwards as tundra habitats fragment and disappear. 
"The problem is that in mountainous areas you can only go so 
high so they get forced into smaller and smaller areas," said 
Danby. 
Danby added that the changes are of particular importance in 
these northern regions where indigenous people still rely 
heavily on the land. 
Caribou and sheep populations have already declined across 
southwestern Yukon, he said. cr.middlebury.edu 





 

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