The most widespread tree in North America is hard to find in Southern Oregon.
Quaking aspens thrive from Maine to California and from Alaska to Mexico, but they’re scarce in the Rogue Valley. You can see occasional specimens here and there, where an ambitious gardener or landscape architect has brought them in, but Populus tremuloides struggles with our summer heat and dry winds.
Aspens are hailed everywhere for their spectacular fall colors. You can see a few scattered aspen stands close to home (in the Siskiyous, west of Mount Ashland and on Wagner Butte) but if you want to see big stands of Wild West aspens, you have to go east — to Klamath Lake.
Aspens thrive all over Klamath County, but the easiest ones to see grow along a five- to six-mile stretch of Highway 140 near Rocky Point. The Klamath Basin’s higher elevation provides just what aspens like — relatively cool summer days and abundant winter snow.
Every year around this time the trees light up in spectacular shades of yellow, orange and gold before shutting down for the long Klamath winter. There’s more to aspens than fall color, however. Some scientists now recognize them as some of the oldest and largest living things on Earth.
Aspens were cloning themselves long before scientists started to duplicate sheep and cats. They reproduce by sending up new shoots from the roots. Every shoot has the same genetic material as its parent tree, so in one sense they’re the same organism.
"There can be thousands of trees in a clone," says Bill Ripple, a forest scientist at Oregon State University.
Individual aspen stems don’t live much longer than 100 years. When the big trees die, the smaller ones take over.
"Some of the clones may be thousands of years old," Ripple says. "The process continues indefinitely."
Each clone runs on its own clock when it comes to fall color. Some even have their own shade of yellow. When clones intermingle, fall-color fans can see shades of yellow, orange and gold close to green trees from another clone that’s on a different timetable.
The bright colors, of course, were always in the leaves, masked by chlorophyll, the chemical that allows trees to synthesize food from carbon dioxide and water — and also gives them their green color.
As the days get shorter, trees prepare to shut down for the winter. The first step is to stop making chlorophyll, exposing the carotene pigments that are also in the leaves.
After a hard frost, the leaves come down.
While aspens are widespread, they are vulnerable to wildfire. Aspen bark, with its distinctive shade of pale gray-green, is thin and provides little protection against fire, but the roots quickly send up new shoots when adult trees are killed by flames.
Researchers have counted more than 100,000 shoots per acre under optimum conditions.
Human efforts to suppress wildfires during the past century, however, have made life more difficult for aspens. Without fire, other tree species often invade aspen groves. The aspens need bright, full sun, and they’ll die if invaders such as conifers overtop them and shade them out.
Ripple says aspens face threats in some areas from overgrazing by livestock. The trees also may have been affected by the disappearance of wolves from much of their range.
Elk and deer like to eat aspen shoots just as much as cattle. Ripple’s study of aspens in Yellowstone National Park indicates that aspen stands that were in decline through much of the 20th century have revived since wolves were reintroduced to the ecosystem.
The wolves have killed and eaten a number of elk, but their mere presence also seems to change the way elk behave. Ripple calls the phenomenon "the ecology of fear."
When elk no longer have to worry about wolves they tend to stay in one place longer, eating the tender young aspen shoots down to the roots. With wolves in the neighborhood, elk spend less time in any one place. The young aspens suffer less damage, and some can eventually grow large enough to replace the mature stems in the clone.
The aspens’ bright fall colors will last until the leaves come down — usually after the first hard frost. That could come at any time, so if you want to see them at their best, now’s the time.
Reach reporter Bill Kettlerat 776-4492, or e-mail bkettler@mailtribune.com.
