A Walk in an Aspen Stand

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Back in Wisconsin, aspen suckers grew like weeds after an area was logged. It came as a surprise to learn, when I moved out West, that here aspens are in serious decline and the focus of conservation efforts. Above is a stand that we’re going to be building a fence around soon at work, to protect it from damage from cattle, deer, and elk.

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It’s doubtful that elk actually spend much time in this pasture anymore (though they’re definitely around in the hills), but the dark scars on the trunks of the trees come from elk scraping at the bark with their teeth to get at the nutritious, photosynthetic layer of bark under the white outer layer.

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While aspen trees do produce flowers, most of their reproduction is vegetative, in the form of new shoots or “suckers” growing from existing root systems. Young, tender suckers are super tasty food for deer – the ones in the photo above, growing in the shelter of a fallen adult, have been heavily browsed. Fencing the deer out of the stand will help young trees get established.

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The way suckering works is actually pretty interesting – the crown of the tree produces a hormone called auxin that inhibits the production of suckers. When the tree falls and auxin is no longer produced, the growth of new suckers increases in response to keep the stand going. An aspen stand is really one big organism, interconnected by the root system that keeps on living even as individual trees die and are replaced. One particular aspen clone in Utah is a candidate for the world’s largest, oldest organism.

There are multiple reasons for aspen decline in the West, including the removal of top predators from ecosystems (no wolves -> more elk and deer -> more browsing of aspen) and the suppression of natural wildfires, which allows other trees like junipers to become established and crowd out aspen. Climate change is almost certainly playing a role, as well. More information:

Aspen Caterpillars?

Last spring when I first noticed these fuzzy oblong shapes in the grass along the path, at first I mistook them for caterpillars.

001Upon closer inspection, definitely not caterpillars. These are the catkins (male flowers) of aspen trees, and they are all over the place right now. Another sign of spring.

Aspen Galls

I promised you a little winter tree ID. Well, clumps of these young trees grow along our trails in abundance, particularly in fairly open areas. Know what they are?

Okay, I kind of gave it away with the title of the post – these are young quaking aspen, Populus tremuloides. Even when they’re this young, their smooth, pale bark and tendency to grow in clusters (the form “clonal colonies,” with many trunks growing from the same set of roots) give them away. They’re an early-successional species, meaning they’re one of the first trees to grow back in an area that’s been disturbed. Another thing to look for is pointy reddish buds. On the trees here, many of the buds have swollen, almost bubbly-looking areas at their bases.

These are galls, caused by a fly called the poplar twiggall fly laying its eggs at the bases of the buds. They’re generally not harmful to the tree.

Do you have aspens where you are? In the fall their leaves turn a beautiful golden color, and as far as I’m concerned they’re one of the most beautiful trees in the North Woods.