Treeline and Global Warming

Looking at our local mountains, it’s easy to assume they’ve always been the same: trees in the valley, a treeless (alpine) area above, and the same rough treeline between.

In spite of appearances, the treeline is anything but stable. The last ice age ended about 11,000 years ago and ever since the treeline has, with some set-backs, moved inexorably back up the mountains.

Treeline is the leading edge of the forest, the front lines in the forest’s attempt to move higher. Limiting that movement are the difficult growing conditions beyond the forest border. Without the protection of other trees, seedlings in the open are buffeted by winds and suffer from more frost damage and desiccation. Depending on climatic conditions, sometimes they survive, sometimes they don’t.

When the climate cools, like in the Little Ice Age (from the 1600s to the mid-1800s), seedlings can’t survive and the treeline moves lower – as shown by trees extracted by researchers from glaciers. When the climate warms, as it has for the last 150 years, snow melts earlier, glaciers retreat, and the treeline marches back up the hill. Recent tree “invasions” have been reported from Garibaldi Park, Vancouver Island, the Canadian and U.S. Rockies, and as far away as the Himalayas.

Which brings up the subject of global warming. The main worry about global warming isn’t the warming itself: temperatures have fluctuated wildly throughout the earth’s history. It’s the rapidity of the warming and its unknown consequences on global weather patterns. So far its likely some areas will get wetter, some drier, and some may even get cooler. There’s lots of theories but nothing yet certain.

If the only thing to happen in the future is warmer temperatures, treeline is likely to move higher. But if the timing of precipitation changes and we get more snow in winter or less rain in summer, treeline could actually move lower (as expected for some subalpine forests in Argentina).

What is pretty certain is that there’s more tree skiing available now than 100 years ago. Whether there will be more or less tree skiing in Whistler’s future (or any skiing at all) is less certain. For more on this subject, watch for Karl Ricker’s report next week on how local glaciers have fared over the past year (his early results show a slight retreat).

Upcoming Events:

September 23 – A Day in the Alpine. 10:00 a.m. to 4:00, Whistler Mountain. Meet for a 10:00 upload at the Whistler Gondola. We’ll have informal presentations by Jack Souther (geology), Nancy Ricker (birds), and other naturalists on flowers and alpine ecology. Bring a lunch and your season’s pass (or you can purchase a sightseeing ticket).

September 23 – Wedgemount Glacier Measurement, 7:00 a.m. at the trailhead. For a more rigorous day, join Karl Ricker on a (very full) day trip as he does his yearly survey of the state of the glaciers.

Written by: Bob Brett



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