Wolves linked to vegetation improvements
By Amber Travsky
March 18 ,2004, Wyoming Tribune-Eagle newspaper.
This disappearance is puzzling, especially since aspen grows rapidly and can quickly resprout from its extensive underground root systems or from seeds after fires, floods, and other disturbances.
1997, William Ripple,
had several theories on the cause of the decline,” Ripple said in an interview
To answer the question, the researchers studied tree rings, tree size classes, and aerial photographs of the park. “We took core samples of the aspen to count the rings,” Ripple said. “From that data we developed an age structure for the aspen.”
The results were surprising. Ripple discovered the aspen quit regenerating in the 1920s. For 70 years, young aspen hadn’t faired well, with few surviving to become mature trees.
About the same time that the aspen quit regenerating, wolves were eliminated from the park. Ripple said the timing begged the question: Is there a connection?
“We developed the hypothesis that there was some link among wolves, elk and aspen,” Ripple said.
The primary culprit for the loss of young aspen was elk feasting on the sprouts. The elk browsed in the willow bottoms and other open country, leisurely gobbling up tender young trees, shrubs and grasses.
absent, the elk grazed anywhere they liked and for decades have been
able to kill, by browsing, nearly all the young aspen. Other streamside species such as willows and
berry-producing shrubs also suffered.
That in turn began to play havoc with an entire streamside ecosystem and
associated wildlife, including birds, insects and fish.
Wolves were reintroduced to
Some ten years ago
"The first thing that happened was that the elk ignored the wolves," said Wildlife Conservation Society senior scientist Joel Berger in a recent interview with Guy Gugliotta of the Washington Post. "The elk were treating 90- and 100-pound wolves like they were 35-pound coyotes,” Berger said. “The elk were naive. They aren't naive anymore."
biologists are noticing improvements in
the streamside vegetation. Ripple
and his colleague Robert Beschta recently released the results of two studies
that indicate wolves may be closely linked to recent changes in cottonwood
trees and willow shrubs. Their research
has focused on
Ripple credits the changes to the wolf reintroduction. In some areas, elk are no longer free to browse in the willow areas unless they want to risk becoming a wolf dinner. "For 70 years, the elk congregated next to the rivers, eating the vegetation," he said. "They don't do that anymore and the changes in vegetation are a direct result of wolves being reintroduced.”
Ten years ago,
Yellowstonenorthern herd had 17,000 elk, the largest single population in the world. Elk, not surprisingly, have suffered, both from weather and wolves, their numbers in the park shrinking to about 8,000 today.
The changes don’t just stop with wolves, elk and willows. Ripple said research is showing other improvements. In 1996 beaver were scarce and there were no known colonies in the
. Now there are seven colonies because the beavers can eat the low-hanging willow branches. The beavers build dams, creating marshland that brings back the otters, mink, muskrats and ducks. Lamar Valley
Fish in the stream benefit from the improved willow and cottonwood vegetation. “Trout are attracted to shaded areas of a stream,” Ripple said. “With more shrubby vegetation, there’s more shade. It’s an ecological chain reaction that can go on and on.”
Ripple said it is the first time in 70 years, that the park has a complete suite of predators and prey. “This is just the beginning of a grand experiment,” he said. “It will take several decades to understand all of the interactions.”
On the Web: for more information on connections among wolves, elk, and vegetation, go to www.cof.orst.edu/wolves.