Aspen, Oak and Other

Jan 28 - I received a question about the vegetation in the area. In addition to sage brush and some grass, there are four types of trees that grow here, aspen, oak, pine and spruce. I started on this topic a few months ago in Afternoon Drive but was talking more about the elevation the trees grow at rather than the trees themselves.

The photo above is from my front yard. The trees on the right are mature oaks. The two taller trees on the left are young aspens. To be more specific the aspens are bigtooth aspens, Populus grandidentata. Even in the winter you can tell they are bigtooths because the bark at the bottom of the trunk has furrows. The furrows will become bigger, more numerous, and darker with age. See below. In North America when you say “aspen” most people think of the more common Quaking Aspen, Populus tremuloides. Those trees have gorgeous smooth white bark.

Furrows in the Trunk of Bigtooth Aspen (with bear scratch)

Aspens are deciduous, turning a beautiful yellow in the fall. They are short lived trees but can still reach a height of 110 feet but typically only reach 50-75 feet. Which is why I said the aspens in the front yard are young. Ours are short and have starting showing furrowing but some white bark is still visible at the base. The base of the trunk will continue to darken as they age. When the tree dies, only the top part dies. The roots will then put up new shoots. This ability allows aspens to quickly grow back after a fire. It also means that aspens are usually found in groups. This makes me suspect my two were planted.

Aspens are in the same family as cottonwoods, Populus. They even have the similar leaf shape to cottonwoods.

Trying to be Poplar: Masquerading as a Cottonwood

We’ve received 18 inches of snow in the last two days which has left cottony puffs of snow in the tree’s branches. But, while it grows among poplars this is an oak. Thus I have made a brainy joke that only an arborist would get by knowing that this oak grows alongside aspens, which like cottonwoods, are poplars.

(I should point out that the tree in the photo above is at the end of someone’s driveway. They have piled snow around the base of the tree to a depth of about 5 feet. So you can’t see the trunk. The diameter at the base is probably about 5 or 6 inches.)

Gamble Oaks, Quercus gambelii, are not what most people east of the Rockies would think of when someone says “oak.” Gambles can be like the one above, that looks like a small single-stemmed tree. They can also look more like a blueberry bush or forsythia. That is, they can be very brushy with lots of stems coming up in a clump. Just like aspens, if there is a fire, the top can burn but the roots can survive and put up new shoots. The roots can live hundreds of years but even without a fire or being trimmed the tops will die back. If a person or animal trims off the shoots, several more shoots can come up around the one that was cut off. Examples like the one above, that has a lone trunk are found in the wild but they’re not the norm. If you look closely you can see houses on both sides of the oak. Someone has been tending this one. If you look back at the first photo in this post, all those trees on the right are probably coming from the same set of roots. In the first photo, in the background on the left, behind the aspens, you see another group of oaks; that’s probably a second plant.

Many people from Colorado think of these oaks as brush. But, they provide shelter and food for many animals including the grouse I blogged about in Jan 25’s post. In addition to birds; chipmunks, squirrels, deer, and even bear depend on these oak’s buds, leaves, bark, and acorns for food. The Colorado state butterfly, the Colorado hairstreak, Hypaurotis crysalus, spends it’s entire life cycle in Gambel oak thickets. It is a really pretty butterfly. I am hoping to see one this summer.

Hypaurotis crysalus, Colorado hairstreak butterfly*

*from https:/www.butterfliesandmoths.org

Next door to the tree in Masquarading as a Cottonwood is this Gambel oak.

I took both photos on the same day. Why then does one tree have no leaves while the other doesn’t look like it has lost a single leaf? Like all other oaks, and many other species of deciduous plants, in autumn, a layer of cells grow at the base of the leaves which close off the veins that supply nutrients and water to the leaves. When the leaves no longer get nutrients or moisture, they fall off. If a plant experiences freezing conditions prior to growing this layer of cells, the leaves will die but the leaves will stay on the plant. This is more common in very young plants. It’s called marcescence. It’s an advantage in some ways because the leaves protect new buds from loosing moisture in the wind and from being eaten from all those hungry animals I talked about earlier. It can also be a disadvantage as all those leaves hold snow which can break a limb. I had wondered why this group of trees was marcescent. They are at the top of the hill so they probably have less shelter from wind so freeze before the tree next door.

Next time you’re driving around, notice that some types of trees still have their leaves in winter, that is marcescence.

When I’m sit at my desk, looking out the window, I also see evergreens. These are spruce, pine, Douglas fir, and juniper. The photo above is the view from my office window. And no, you can’t move in with us to enjoy the view. You will notice that the foreground is the aspen and oaks from earlier.

Since they are across a valley and up a mountain with no road, I can’t tell you what kind of tree they are. But you can identify spruce by knowing that the needles will grown from the branch singly and will be square. Colorado spruce have needles that grow at 90 degrees from their branches. Engelmann needles grow at about 45 degrees from their branches. We have both species of spruce in the area.

If the needles were flat and carried singly it would be a fir tree. Their cones also stand upright rather than hang down. In this location we don’t have any true fir trees. Douglas firs are not considered true fir because their cones hang down.

If the tree’s needles came from the branch in bundles of 2, 3 or 5, then it’s a pine tree. Here we have both Colorado pinyon or ponderosa pine. These should be easy to tell apart as pinyon pine only reach about 30 ft and are just as wide at maturity. Ponderosa pine can reach 250 ft and are the tallest trees in the area unless they are young. While a young ponderosa might be the same height as an old pinyon their growth habit will be very different.

If I ever happen to climb that mountain, I’ll take some close up photos of their needles, bark, and structure and to see if I can identify what kind of trees I find.

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