Polar Bear Blog – A Tale of Two Treelines

Churchill lies along the treeline. This is the northern edge of the boreal forest, a giant swath of evergreen trees that stretches across much of northern Canada. When you drive out east, you can see the treeline just a few kilometres inland. However, tree islands and small clumps of tree are found out on the thin line of ‘tundra’ that parallels the coast of Hudson Bay.

Well, basically, there are two ‘treelines’. The main treeline is the northern extent at which spruce trees have enough warm days to grow and reproduce. This treeline extends from, essentially, Churchill northwest to Great Slave Lake and then further north to Inuvik in the west arctic.

The modern treeline is kind of a rough outline of the last major glaciation and its retreat in North America. The last ice of the glaciers was actually found from Arviat stretching north to Repulse Bay, west to Baker Lake. Smaller amounts were present in Nunavik, Quebec. Glacial ice from our last ice age actually remains only on Baffin Island, all of the Rocky Mountain glaciers in the west are around 5,000 years old.

The secondary treeline could almost be considered a ‘phantom treeline’. There are pockets of trees that hold out due to sheltered microclimates but also trees growing right out in the open tundra, exposed to the elements. These clumps are quite often just one tree. The conditions are too difficult to produce seeds (cones) so these trees actually grow ‘out’ instead of ‘up’. Basically, cloning instead of reproducing.

When conditions are warm enough, these ‘clones’ will start to grow upwards like a normal tree. Through this action, you end up with these clumps where one larger tree can be found in the middle and a series of smaller trees ring around it. In a strange way, these smaller trees likely aid the main tree by gathering snow and protecting it from the cold winter winds.

Most commonly this occurs with black spruce, a rugged tree adapted to muskeg conditions prevalent in the north. Churchill is one of the very few places in the planet where White Spruce will ‘clone’ in this fashion, due to the arctic influence of Hudson Bay and its southern location.

What is interesting is that these trees are actually a glimpse into the past. About 3500 years ago, the treeline extended over 200-300 kilometres north of its present location. Once the climate cooled, the treeline migrated south leaving a few holdouts along the way. Churchill’s trees, of course, are much younger as this coastline was still underwater at that point.

This phantom treeline has disappeared in many parts of the arctic, used by Inuit, whalers and explorers as fuel or building materials. Given that these trees no longer can sexually reproduce, once these clumps die off through fire or human impact, they will not return. At least, not until the climate warms enough for the treeline to once again migrate northwards. So be careful!

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