How much rain could a rainforest get, if a rainforest could get rain?

Bamfield Marine Center is located in a temperate rainforest, which means that it gets a lot of precipitation. But how much precipitation is a lot of precipitation? And why do I say precipitation instead of rain? In temperate rainforests such as Bamfield, moisture can come in the form of rain, hail, snow, and fog. All of this adds up to about 2846 mm per year! In contrast, Vancouver, a city that prides itself on getting a lot of rain, only gets 1,199 mm per year. Luckily when we went on our nature walk through the forest it was a bright clear day, which is unusual since Bamfield receives precipitation 193 days of the year.

So what does all of this rain mean for the kinds of things that can grow here? Because of all the rain, many of the nutrients and things trees need to grow get washed out of the soil by the water. This is good news for the marine systems that receive all of this run off, but for the forests it means that there aren’t a lot of nutrients left. Because of the way dead matter accumulates and decomposes on the forest floor, the top layer of soil is typically the most rich. All of this means that in order for trees to get the nutrients they need to grow, their roots have to grow out instead of down. With the large amounts of precipitation the forest relieves the tree roots don’t have to go very deep to reach moist soil, so they’re quite happy to stay surface level. All this moisture means that the forest floor is quite muddy, which can be a problem if you don’t stick to the trail and get stuck!

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Stuck in the muck! Photo credit: Emily Lim

Shallow roots work great for getting nutrients and water, but when strong wind storms come along the trees are very poorly rooted and are vulnerable to getting toppled over. In fact, in these forests wind storms are the largest source of disturbance! All of that rain keeps things nice and damp, so forest fires aren’t as much of a risk here as they are in drier climates. When trees are toppled over by storms, they become part of the decomposing matter that will provide nutrients for generations of trees to come. The dominant tree in Bamfield’s forest is the Western Hemlock. It’s quite common to see a bunch of hemlocks all perfectly in a line, and it’s not because of tree planters! Hemlocks will often start growing out of a fallen tree, called a nurse log, such that you end up with a whole line of them along the dead tree. Eventually, the new trees grow and the dead one decays, leaving you with a perfect line of hemlocks.

Check out http://wwf.panda.org/about_our_earth/ecoregions/pacific_temperate_rainforests.cfm if you want to read more about temperate rainforests and the things living in them!

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