A Closer Look: Quaking Aspen

Any comprehensive survey of the Colorado’s treescape would not be complete without a solid mention of the quaking aspen. In fact, the quaking aspen is so bountiful in Colorado that it covers an area that spans 5 million acres of land – that’s 20 percent of the forested area throughout the state! This deciduous tree can be found at elevations of ranging from 6,500 to 11,500 feet, particularly west of the front range throughout the West Slope. Ideal growing conditions include moist, well-drained soil with a more acidic pH that is more often found at such high altitudes. For this reason, you are not likely to to see many quaking aspen in Denver, as conditions are not ideal for them to thrive.

In honor of this majestic native species, we couldn’t help but dedicate an article to our readers profiling the quaking aspen, and luckily came across some fantastic detail in the book Around The World In 80 Trees. We highly recommend reading through the entirety of the book (which is also beautifully illustrated), but in the meantime, enjoy this passage on the quaking aspen…

Photo by Logan Fisher on Pexels.com

The most widespread North American tree species, the quaking aspen, thrives in the high country of the west, especially in Colorado and Utah, where it is the state tree. A stand of aspen makes the heart leap. Its leaves flicker and shimmer, vivid green on top and pale grey underneath, becoming first yellow and then brilliant gold in autumn, glorious against clear mountain skies. The leaf stalks, or petioles, are long and flattened like ribbons so that leaves bend and twist in the slightest air, rustling with the soothing sound of a rippling stream. Nobody knows for sure why aspen leaves have evolved to quiver. One theory is that the flexibility of the stalks helps aspens to avoid having their leaves stripped by mountain winds. The constant movement might also allow light to filter through dense woods to the aspens’ pale trunks, which – tinged green with chlorophyll – can also photosynthesize.

The aspen hates shade. It can’t reproduce beneath its own canopy, let alone compete with a blanket of pines, but after a fire it can quickly repopulate fire-cleared ground before other species. That is why there are often whole groves of aspens of exactly the same height, having all sprouted simultaneously. Out west, where dry spells make life hard for seeds, aspens abstain from sexual reproduction and instead generate new tree stems directly by suckering. What look like separate trees may actually be genetically identical tree trunks rising from a common root system, collectively known as clone. In fact, the heaviest known living organism on the planet may be a single stand of quaking aspens in Utah, affectionately called Pando (Latin for “I spread”), which contains 45,000 trees, covers more than 40 hectares (100 acres) and probably weighs 6,500 tons. The colony (but not any individual tree) may be 80,000 years old.

The risk of reproducing this way is that plants may lack the genetic diversity to overcome disease or to adapt quickly to a changing environment. However, distinct aspen populations are remarkably diverse and can also revert to sexual reproduction; as a result, the species are very successful. Counter-intuitively, one of the main threats to large groups of aspen is the presence of protected areas and visitor centers with campsites. This is not because of what campers might do to the trees, but because fire in such places is more likely to be controlled or extinguished, giving the edge to competing shade-tolerant conifers.

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