Quaking Aspen: Species of the Week

This time of year, I’m one of many throughout the West enthralled by – and worried about – one of our most striking fall color trees: Quaking Aspen (Populus tremuloides ). Utah and Colorado have acres and acres of aspens.  In northeast Oregon, we have smaller groves dotting the more prevalent bunchgrass slopes and ponderosa pine forests.

Partial view of a one acre aspen grove in eastern Oregon, October 2009.

I’ve become particularly fond of an acre of aspen we see from our yurt.  Our year-round spring bubbles up at the corner. But I’m worried because some of the older trees there are dying.

Throughout the West, aspen trees have been disappearing, though experts disagree on whether the declines are widespread or part of localized processes of natural forest succession. The causes are not agreed upon, but scientists point to climate change, prolonged drought in some areas, lack of fire opening up forest canopies, elk and deer populations that have lost their natural predators, insect infestations, fungal diseases. Of course, the precise causes may overlap and vary from place to place.

Most of my initial reading led me to believe that the trees in a grove share one root system and the same genetic material. Aspen trees sprout from large underground root systems, some of which could be as old as 10,000 years.   Some claim the Pando grove in Utah to be the largest such clone, covering over 100 acres.  It may also be the heaviest and oldest living organism, but those claims are disputed.

Part of the challenge in laying claim to “oldest” or “heaviest” is figuring out what makes-up a single organism.  And not all aspen groves are single clones. For example, researchers in Rocky Mountain National Park discovered a surprising amount of genetic diversity in trees growing next to one another. It appears that some trees grow from original parent roots, but others grow from windblown seeds that sprout and form new root systems among the older ones.

This genetic diversity is more than intriguing. It means that some aspens in a particular grove may adapt to local stresses better than others and (perhaps with a little help from fire or fencing) be the foundation of renewed growth.

Young aspens sprouting among older ones with damaged trunks. Large ponderosa pines like the one in the background also shade the trees and reduce growth.

I have no idea what kind of root system we have.  But several foresters have visited our place and assured us that our grove has good “reprod.” We do have a lot of young sprouts – thickets of them actually.  The greatest worry is for aspen groves that have no young sprouts, and unfortunately there are many of those throughout the West.  Perhaps our grove is just going through a natural phase where young trees replace the older ones, and all we need to to is put up a fence to keep elk and deer from browsing and rubbing on the trees.  We also need to cut down some large ponderosa pines that have invaded the grove.  Aspens don’t like shade.

Meanwhile, if anyone knows of other research or resources on protecting and restoring aspen groves that might prove useful, I’d love to hear about them.

Coming Soon: Photos of fall color, including many more aspens.

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Further Reading:

Biogeography of Quaking Aspen

Regenerating Quaking Aspen: Management Considerations

Cross-posted as Biodiversions at The Clade.

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