More to Tracing Aspens' Family Tree than Meets the Eye

New research from Utah State University suggests that identifying the lineage of similar-looking groups of aspen trees may not be as simple as once thought. USU geneticist Karen Mock and colleagues have discovered clusters of aspen in Utah’s Logan Canyon that, though close in proximity and appearance, are genetically dissimilar.

Mock was among the presenters at USU’s recent Restoring the West Conference, which focused on aspen restoration. The gathering was hosted by USU’s Ecology Center, the Department of Wildland Resources, Cooperative Extension, the USDA Forest Service Rocky Mountain Research Station and USDA Forest Service State and Private Forestry. It attracted more than 150 forestry professionals and scholars from throughout the West.

A valued forest resource, aspen trees provide scenic beauty with their distinctive, shimmering leaves – which merit their nickname, “quakies.” These stands are also important as wildlife habitat, and their understory provides excellent forage for livestock.

Ensuring the health of these forests has long been a topic of interest for forest managers in the West, and in recent weeks this issue has played prominently in national media outlets such as The Washington Post, CNN, MSNBC, National Public Radio, The New York Times and USA Today.

Aspen management requires different strategies than are used for other forest types because the life cycle of aspen is fairly unique. Although aspen produce viable seeds, successful seedling establishment is thought to be very rare in the dry conditions found throughout most landscapes in the West. Instead, the trees’ primary means of reproduction is to send up new root sprouts, called “suckers,” from an existing root system. These suckers are genetically identical to the root system from which they sprung, and the entire system of trees and roots is called a “clone.”

Until now, forest managers were taught, and have taught others, that distinct aspen clones could be easily identified by looking for similar patterns in branching habits and leaf color and size. Mock’s findings suggests otherwise. Based on her research, Mock, an assistant professor in the College of Natural Resources’ Department of Wildland Resources, explains that the similar leaf and branch characteristics traditionally used to identify clones “are not perfect predictors of genetic identity.”

In order to determine the genetic makeup of one supposed aspen clone, Mock and colleague Ron Ryel, also an assistant professor in Wildland Resources, and conducted research on a cluster of similar-looking aspen trees on Swan Flats near the summit of Logan Canyon. Aided by student researchers, Mock and Ryel collected leaves from more than 800 individual trees at the site, which covers several square miles.

Early results of genetic analysis performed on the leaf samples indicate that the aspen stands at Swan Flats are much more genetically diverse than most foresters would have guessed by simply looking at the stand. This finding suggests that managers cannot base decisions on the visual characteristics of aspen they have used in the past. It also suggests that the directing principles of aspen ecology might prove to be inaccurate. For instance, although aspen reproduction by seed has been considered extremely rare in western landscapes, it is perhaps the simplest explanation for the genetic diversity at Swan Flats. Another explanation for the genetic diversity at Swan Flats is that mutations have accumulated within the clone, which over time has altered the clone’s genetics.

Further analysis should determine how each mechanism is contributing to genetic variation among aspen at the experimental site. But either scenario could have important implications for aspen management in the West. If aspen reproduction by seed is a more common occurrence than currently thought, managers will have to significantly adjust their knowledge of aspen landscape dynamics. Alternately, if accumulating mutations within a clone can significantly alter its genetics, finding out how these mutations affect aspen health and survival throughout the West will be an important task in understanding and managing these forests.

Finding the answers to these questions is increasingly urgent in light of the high mortality that is currently occurring in many western aspen stands. Conference presenters pointed out that while scientists and forest managers have observed gradual declines in western aspen for decades, in recent years, areas of mass die-offs have occurred. The reason remains a mystery, but scientists speculate that drought, disease, climate change and insects, or a combination of these factors, may be the cause. Finding out how genetics influence aspen response to these threats will be a crucial step in managing these valuable forests and ensuring that quakies remain an iconic fixture of our western landscape.

This article originally appeared in the Summer 2006 issue of Utah Forest News, Utah Forest Landowner Education Program newsletter, a production of USU Extension. It is reprinted with permission.