Is the subarctic treeline moving under global warming?
Did you know?
Trees that grow on mountain slopes can move up, down or remain stable during global warming
  • If the climate is favourable the trees can move upwards.
  • If the slope is steep, has rocks and boulders the treeline stays the same even if the climate is more favourable
  • Insect pests active at the treeline, because of increasing temperatures that allow eggs to survive in winter, can kill the trees so that the treeline can move lower down.
Tree expansion is not welcome in many places .
  • Very biodiverse old hay meadows (they have many species) that are abandoned lose many of their species when shrubs and trees move in. (Experiments moving reindeer on to these meadows show tree growth might be controlled).
  • Reindeer herders like open areas because they can see their reindeer and predators that can hide when shrubs and trees grow.
If climate change continues at the current rate, computer models predict trees may move North by up to 2km a year! However, observations show that the treeline is more likely to move by 100m a year.
As the tree line moves north, it squeezes the tundra zone between the forest and the ocean. As the treeline moves uphill, it pushes Arctic/alpine tundra plants off the edge.
In mountainous places other than the Arctic, there is a lower tree line as well as an upper tree line. The lower one is usually caused by agriculture and grazing animals.

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Moving Treelines
A treeline is known as a limit to where trees can grow. This can be due to low temperatures associated with elevation (altitude) and latitude (although there are many other causes too like deforestation). Climate warming is now shifting the tree's growth limits, allowing trees to survive higher up the mountains and further North.

Where trees are spreading, there can be many problems as well as benefits. One problem is the loss of tundra habitat and many plant and animal species within it. If we look at three different northern landscapes; the taiga (where cold adapted trees are able to live), the tundra (plains that are treeless and only small shrubs can grow) and the high Arctic (an area of ice, mountains and snow with no shrubs or trees), we expect the taiga to invade the tundra and the tundra to invade the high Arctic. This would affect habitats and wildlife, like the Arctic fox and the snowy owl.
Photo: Shutterstock
Photo: T.V. Callaghan
High Arctic
Photo: W. Vincent
Illustration: T. V. Callaghan
Answer the following STEM questions about the rate of treeline movement:
If the treeline in Siberia is 1km from the coast and trees move at 8m per year, how many years would it take for the treeline to reach the coast?
50 years ago, the treeline on a mountain was 600m below the summit. This year, the trees got to the summit and the tundra disappeared. How many meters per year are the trees moving?