JACKSON, Wyo. (AP) - Several studies are being conducted in Jackson Hole on how hoofed species, such as elk, deer and moose, affect the aspen stands, which are on the decline across the Rocky Mountains.
In one study on the National Elk Refuge, published in the Intermountain Journal of Sciences, researchers clear-cut aspen stands to spur new growth.
Older trees in an aspen stand produce a chemical that limits production of new sprouts, called suckers, from the root system. When the older trees are killed, the chemical production diminishes, allowing young suckers to sprout.
Researchers compared the growth of clear-cut aspen inside fenced areas, designed to prevent elk browsing, to clear-cut stands that were not enclosed.
The study found that all stands produced lots of suckers. But over time aspen inside the fences had higher densities of saplings tall enough to escape browsing on the highest buds, allowing them to grow into mature trees and replace aging stands.
Another study by University of Wyoming graduate student Eric Anderson documented a similar trend comparing 30 aspen stands - 15 near elk feedgrounds, including the Refuge, and 15 distant from feedgrounds.
Anderson found higher densities of saplings tall enough to increase the likelihood of escaping browsing from animals and growing into mature trees in stands far from feedgrounds.
Anderson also studied bird species using the aspen. In stands with lots of shrubs growing around their base, he found higher densities of songbirds, such as the MacGillivray's Warbler. The warbler is among birds that nest and forage in these shrubs, which are called the understory.
Those species were less abundant near elk feedgrounds where elk browsing reduced understories.
But Anderson found higher densities of cavity-nesting birds, such as Downy Woodpeckers and Red-naped Sapsuckers, near feedgrounds. In fact, as elk strip bark from aspen they allow fungi and insects easier access to the trees. More decay and insects mean more nesting cavities and food for woodpeckers and sapsuckers.
Overall, he found bird densities about equal in stands both near and distant from feedgrounds, he said.
But observations that stands near feedgrounds are not producing enough saplings to replace aging trees suggests those stands could eventually convert to sagebrush, eliminating habitat many birds depend on, Anderson said.
In a separate study, researcher Joel Berger found less diversity among songbirds in willows where moose had no natural predators. He documented greater songbird diversity in areas where human hunters have limited moose numbers.
But Colorado State University scientist Tom Hobbs said he is not convinced reducing elk numbers would cause aspen and willows to rebound.
Even if the elk population is cut in half, he said, "You may see very little impact on those woody plant communities. They may be heavily used because they are rare and they are preferred."
Wolves may be a more important factor than elk numbers in limiting habitat damage, Hobbs said.
A group of Oregon researchers, who studied the tree cores of aspen stands in Yellowstone National Park, found that new trees stopped growing tall enough to join the canopy about the same time wolves were exterminated from the park.
Today, those researchers are monitoring how wolves, which were reintroduced to Yellowstone in 1995 and 1996, may be altering elk movement and eating patterns.
Already, observers in Jackson Hole and Yellowstone have witnessed wolves herding elk.
