Just east of Bridal Veil on the Historic Columbia River Highway, a colony of white-barked Quaking Aspen (Populus tremuloides) suddenly appear along the road, seemingly transported from somewhere in the Rocky Mountains. Though these are North America’s most widespread tree species, they are uncommon in Western Oregon.
Many who spot these unlikely trees might reasonably assume they were intentionally planted here, given the nearby residential district. That’s possible, but it’s more likely that this is a native stand, one of only a few sprinkled on the western fringes of the aspen range, where it extends south from Canada along the eastern crest of the Cascades.
The stand is easy to find: drive one-third mile beyond the Angels Rest trailhead in the Bridal Veil area and watch for the trees on the south side of the road. There’s room to pull off, but use caution before wading in — this might be the only Aspen grove in Oregon with knee-deep poison oak! The stand is also fringed with lupine, coltsfoot and many other wildflowers in mid-spring, making for a dramatic scene.
Topographic maps give a hint as to why Aspen would grow here: marshy, river bottom soils, cool mountain air flowing off Larch Mountain and down Coopey Canyon and the generally brisk Gorge winters mimic prime aspen habitat. The grove also appears to be on public land, within Shepperds Dell State Park (see map, below).
It’s hard to know the future of Oregon’s aspen trees, given the expected effects of climate change on most northern species. The following map shows just how fragile the aspens along the Cascade Range are compared to the broad habitat found in the Rockies, Great Lakes region and Canada:
Even more isolated and fragile are the groves that dot the basin and range country of Southeast Oregon. These are the aspens growing on alpine islands in the desert, including Steens Mountain, Hart Mountain and a few other tall peaks in the high desert country.
Ecology of the Aspen
The name “Quaking Aspen” comes from the unique trembling that the slightest breeze creates among the leaves of Aspen trees. This is also where the botanical name of “tremuloides” is derived.
The “quaking” comes from flattened petiole, or stem, that connects the leaves to tree branches, and vibrates in the wind. The soft rustling is unmistakable to anyone who has spent time in Aspen country. Though Aspen are famous for their brilliant yellow fall color, the Gorge grove tends to be a paler yellow, possibly reflecting the milder fall temperatures at the site, compared to typical Aspen habitat.
Quaking Aspen reproduce mostly through root sprouts, with the young trees called “clones”, since they are genetically identical, and usually still connected to the parent tree. Whole groves of Aspen often consist of clones from a single originating tree, and share a single root system, and are thus called clone colonies.
This shared root system help explain why these colonies leaf out in spring and abruptly turn color in the fall as a complete unit, but often out of sync with nearby colonies running on their own clock.
The survival advantage of a clone colony can be seen in the Pando colony in Southern Utah, located high on the Colorado Plateau. Scientists estimate the 100-acre colony to have nearly 50,000 individual “stems” (trees) in the grove, all sharing a common root system. Amazingly, the root system is estimated to be at least 80,000 years old, with some scientists estimating the colony to be over million years old. This makes the Quaking Aspen both the oldest and largest organism on the planet, as defined by a continuously living DNA marker.
One disadvantage of clone colonies is that Aspen trees come in male and female varieties, and thus the clones in a colony are usually the same sex, making seed production more difficult.
Even when Aspen seeds are produced, they lack sufficient food and coating to make them durable enough to survive for long in harsh environments. This could be why Aspen rarely grow from seed, but also underscores the vulnerability of the species, since seed reproduction allows a species to migrate much more quickly in period of rapid climate change.
In the mid-1990s, scientists began to notice a mass die-off in Quaking Aspen trees across the Western US. Often, the older trees in a grove were afflicted, but increasingly, entire clone colonies have died. There are a variety of theories about the decline, though most attribute it to a combination of changing climate and a century of fire suppression.
Like most western trees, Aspen are well adapted to fire, and quickly spring back after a burn, since the common root system of a colony is generally left unscathed, even if fire kills most of the trees growing from the root system. Under this theory, the die-off is a response to older Aspen groves simply outliving their viability, and abruptly falling victim to disease.
Another theory focuses on the drought conditions that have plagued the west during the past two decades. Some scientists believe this has simply left Aspen too stressed to cope with insects and diseases that normally not be life-threatening to the trees. One study showed that more than 80% of the die-off has occurred in areas predicted to lose Aspen trees as a result of climate change — usually south-facing and lower-elevation habitats. This evidence also reinforces the risks that climate change will eventually bring for the Aspen forests.
Yet another theory is that over-grazing is causing the decline, with young tree sprouts being grazed before they can reach maturity, and replace older trees within a grove. In a unique study of wolves at Yellowstone, a variation on this research showed the same relationship where deer and elk populations were not checked by predators, causing a similar decline in Aspen colonies.
The phenomenon is now known collectively as “Sudden Aspen Decline”, and is the focus of much concern among researchers.
Though the die-off seems to be slowing in recent years, thanks to record rainfall in several previously drought-stricken areas, the damage has been extensive: Colorado has lost nearly 500,000 acres of aspen since the die-off began, or nearly 20 percent of its standing aspen. Other Rocky Mountain stands show similar damage, with scientists estimating that Aspen groves surviving today accounting for just 40% of what stood in the mid-1800s.
The Future of the Gorge Aspen?
The recent ecology of Aspen in the west is alarming, but researchers are busy looking for answers. In Oregon, studies are underway on the resiliency of Quaking Aspen in the Warner and Trout Creek mountains, and Oregon State University is providing ongoing research with The Aspen Project.
And what is the future of the Aspen grove near Bridal Veil? The good news is the trees seem to be on public land, and thus easier to protect and manage. New clones can also be seen growing at the edge of the stand, though the trees still face heavy competition from a thicket of underbrush, and a growing canopy of big conifers and Bigleaf Maple. In the long term, these Aspen won’t survive the competition unless the colony is actively managed to help them survive.
Other small Aspen stands dot the Gorge and the western foothills of Mount Hood, including one emerging stand along US 26, just east of Gresham, that might just be the western-most in the state. Much larger stands flank the east slope of the Cascades in places like the Hood River Valley, Metolius River and Klamath Lake.
While these isolated stands are small and remote from the prime Aspen habitat of the Rockies and Canada, that could be a very good reason to help them survive: it’s possible that these intrepid Oregon Aspen will be better situated to survive climate change, and may represent a genetic insurance policy for the species.
Scientists are learning much about Aspen and how to perpetuate the species in the face of the die-off. Hopefully, Oregon’s public land managers will also apply these lessons to the tiny, isolated healthy stands in places like the Gorge, as one more safeguard for an increasingly vulnerable species.