Tree ID: Red Alder trees vs. Black Cottonwood trees

As I alluded to in my New Beginnings for Fall post, I've made it a project to learn more about trees over the last couple of years. I've been examining trunks, leaves, seeds, and cones on my walks, and deepening my tree identification skills by flipping through the wonderful Northwest Trees

For those of you who are new to tree identification, I thought I'd do a quick tutorial on how to tell the difference between a Black Cottonwood tree and a Red Alder tree. Both are trees that grow near streams and wetlands in British Columbia, so you might see them near ponds, lakes, rivers, or other places where their roots can access water.

Let's start with the leaves. Have a look at the following 2 pictures. Can you tell which leaves belong to the black cottonwood tree and which belong to the red alder tree?

Ready? If you guessed that the top image shows red alder leaves and the bottom displays black cottonwood leaves, you are correct! Still unsure? No problem - let's walk through the differences.

Shape: The red alder leaves have more of an egg shape with a pointed top, whereas the black cottonwood leaves have more of a rounded triangular shape.

Colour: The red alder leaves are a bright, fresh, matte lettuce green, whereas the black cottonwood leaves are darker and glossier on top, and whitish-green on the underside. You'll also notice that the underside of a black cottonwood leaf has some golden tones, which are from residual resin left from their springtime leaf bud. Sometimes you can smell this sweet resin on the leaf.

Leaf Veins and Margins: The red alder leaves have a toothed outer edge and very straight veins. The black cottonwood leaves are slightly toothed, but almost smooth on the outer edge, and have an upward curve in their veins.

Are you ready to look at some trunks? Here we go:

An alder trunk - notice the white patches.

An alder trunk - notice the white patches.

The image above is of a typical alder trunk. You'll notice that its outer skin is a greyish colour, but that it almost appears white because of the lichens that grow all over it.

And here is a big old cottonwood trunk. You'll notice that it is quite a bit thicker, browner and more corrugated than an alder trunk. Note, though, that this particular tree is quite old, and that younger cottonwood trunks tend to have thinner skin.

If you are walking near a patch of alders or cottonwoods in March or April, before the leaves have fully shown themselves, there are other ways that you can tell these trees apart. In the springtime, alder trees have dangly bits called catkins that hold the male part of the seed, and small, half-inch cones that contain the female parts. You'll notice the male catkins scattered all over the ground in the early spring.

Cottonwood trees have sticky buds that encase their new leaves in the springtime. Because these buds are filled with resin, you'll often be able to smell a sweet smell when you're walking near these trees in March or April. Once the leaves have emerged early in the season, you may notice clusters of spent buds surrounding the trees.

The emerging springtime leaves of a sitka alder tree, a smaller, shrubbier alder with multiple trunks. 

The emerging springtime leaves of a sitka alder tree, a smaller, shrubbier alder with multiple trunks. 

A black cottonwood branch.

A black cottonwood branch.

A final identifying feature of a black cottonwood tree is that it shimmers when it blows in the wind. I think this might be due to the slight glossy quality of its leaves, or the fact that the front and the back of its leaves are two different tones. One of the places you can see this lovely vision in action is along the Millenium Line of Vancouver's Skytrain. Watching the cottonwoods that line the train trajectory is a great way to add a bit of enjoyment to an otherwise mundane commute.