The landscapes of the Arctic tundra are changing dramatically. Spurred by global warming, low grasses and sedges are being taken over by thick, woody shrubs, some of them growing as tall as a person. Scientists at the University of Minnesota have discovered the key cause of this ‘shrubification’ – June temperatures.
The shrubs grow in rings, similar to trees, though at a tiny scale. A cross section of these growth rings can be measured against historical weather patterns to determine when a plant is growing fastest, and why. By looking at 20,000 individual shrub rings from the North Slopes of Alaska, the University of Minnesota team could see that the rings grew the most during warmer Junes. In fact, other factors didn’t even get a look in.
‘It was a surprising result,’ says Daniel Ackerman, the PhD ecology candidate who led the study. ‘Other variables, including temperatures during the rest of the growing season in July and August, barely had an impact on shrub growth.’ As subsequent June months are predicted to get warmer, ‘we can expect shrubification to continue throughout northern Alaska,’ says Ackerman.
The transition to more shrubby landscapes is predicted to make life more difficult for Arctic species. It particularly impacts caribou herds, as shrubs have been observed to replace the lichen and other delicate tundra plants that they feed on. In fact, many scientists believe the greening of the Arctic is a foremost issue in relation to the mammals’ major decline. Meanwhile, some species may make use of a shrubbier ecosystem. ‘It seems like larger shrubs will benefit animals such as moose and ptarmigan, while others, such as caribou, could be harmed,’ says Ackerman.
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