The following individual(s) were interviewed for today’s show. Our thanks to:

Mike Tatum
District Silivculturist
Prairie City Ranger District
Prairie City, OR
Malheur National Forest

Dr. Vicky Erickson
Geneticist
USDA Forest Service
Malheur National Forest
Oregon

Mike Feiger
Wildlife Biologist Prairie Ranger District
Malheur National Forest

The following web sites and articles provided information relevant to this script:

A May 2001 article from the newsletter Forestry Source about “disappearance of western aspen”:http://www.safnet.org/archive/aspen501.htm. Focuses on role of fire in regeneration of aspen.

Brigham Young University College of Agriculture and Forestry article on “the role of conifers in aspen decline”:http://bioag.byu.edu/botany/Rushforth/WWW/boulder/aspendecline

Good background info about “aspen”:http://bss.sfsu.edu/geog/bholzman/courses/fall99projects/aspen, from a course offered at San Francisco State University Department of Geography

A report on “the connection between healthy populations of wolves and healthy populations of aspen.”:http://abcnews.go.com/sections/science/DyeHard/dyehard000920.html (ABC News)

Author’s notes:

Populus tremuloides-the scientific name for quaking aspen-aptly describes the way the leaves shiver in the slightest breeze.

Aspens are small trees, only 40 to 70 feet tall when nature, with smooth, almost white bark and bright green leaves that turn golden yellow in fall. They often grow in moist soil along rivers and streams, where they provide important wildlife habitat. Woodpeckers are often abundant in aspen groves, because the dead trees are easy to excavate-the core rots while the outer layer of wood stays hard. Sapsucker will often drill into live aspens to release streams of sap that attract insects which the birds gobble up. Game birds such as ruff grouse and blue grouse also flock to aspen stands because the dense foliage provides good hiding places; aspen buds are a nutritious food for these birds in early spring. Black bears, rabbits, and porcupine all like to eat aspen bark, buds, and leaves. Beaver rely on aspen to build their dams and lodges. And during calving season, deer and elk like to take refuge in aspen stands, because they are often conveniently close to water, and cool and moist, while the young aspen shoots provide rich food.

Cloning humans may be controversial, but cloning aspen trees is NOT-the trees do it all by themselves. When you look at a grove of aspen trees, you are often looking at a grove of clones-trees that are genetically identical to one another. That’s because, unlike most other trees, aspens rarely grow from seeds. Instead, new trees sprout from the growing roots of existing trees.

The reason aspens rarely set seeds is that they are what scientists call dioecious-individual plants are either male or female. So a grove of clones will be either all male trees or all female trees, neither of which can make seeds on their own.

Periodic fires seem to be helpful in stimulating new growth in some aspen groves. Fire clears away the old, dead wood above ground, making room for new sprouts to grow. And it also lets in more sunlight, which warms the ground and stimulates growth hormones that cause new sprouts to shoot up. A mature root system can send up as many as a million shoots per acre. It’s easy to see how the century-long policy of fire suppression in the United States may have contributed to the decline of aspen.

Another reason aspens are declining has to do with changes in wildlife populations. We think of the United States as tamed and heavily settled, yet in some places deer and elk are now as abundant-or even more abundant-than they were before Europeans arrived on this continent. That’s because in many places, farm or rangeland has reverted to forest or grassland; meanwhile the big predators that used to keep deer and elk populations in check have been mostly killed off. (Hunting by humans doesn’t do as good a job controlling populations of browsers.) Deer and elk love to eat young aspen shoots, and where these animals are numerous, aspen groves have trouble regenerating. Free-ranging cattle also like to munch on aspen shoots.

Another factor contributing to aspen decline is the growth of other kinds of trees-specifically, evergreens. When grazers browse down aspen shoots, that opens up room for conifers (which are not as appealing to deer and elk) to grow. Over the seasons, as the evergreen trees drop their needles, the composition of the soil in the grove changes. Eventually, even if grazing is prevented the soil will no longer be suitable for aspens.

A researcher at Oregon State University has an unconventional idea for how to make aspen trees grow: release more wolves into the wild. Tests are underway to compare the growth of aspen groves in areas with and without healthy wolf populations.

Dr. Vicki Erickson, a geneticist with the USDA Forest Service who works in the Malheur National Forest in Oregon, has been involved with the effort to do genetic testing of aspen groves in the forest. She says, “In general we found trees within a stand were not very diverse. But we did find several examples in the Sugarbowl and Thompson Creek Drainage where there was a tremendous amount of variation within a stand compared to other stands. Because of this genetic variation, we would consider them a very high priority for protection.” Erickson says other stands that have been given high priority for protection are those with trees that have unique alleles or genes-genetic material not seen in other trees or other stands.

We asked Dr. Erickson why preserving genetic diversity is important-what’s wrong with a forest full of clones? Genetic diversity is generally considered an inherent component of a species potential to exist over the long haul, she replies. “So for that reason it’s important.” For example, most scientists now say there’s compelling evidence that the global climate is warming. A population of aspens that is genetically diverse is more likely to contain trees with traits that will allow them to persist in changing conditions.