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For the week of December 27 through January 2, 2000

USFS combats decline of aspen trees


"Over the last 150 years or so it is estimated that thousands of acres of aspen forest in Idaho have been lost. This loss can be attributed to some of our land management practices, primarily the exclusion of fire."

-Deb Bumpus, Sawtooth National Forest threatened and endangered species biologist


By GREG STAHL
Express Staff Writer

Gold-streaked mountainsides in autumn and the fluttering of aspen leaves during summer—two of the mountain West’s hallmarks—are becoming rarer sites as humans continue to manage the environment.

Though it’s not immediately apparent, aspen tree populations are declining across the West, and have been for more than a century.

"Over the last 150 years or so it is estimated that thousands of acres of aspen forest in Idaho have been lost," Sawtooth National Forest threatened and endangered species biologist Deb Bumpus said. "This loss can be attributed to some of our land management practices, primarily the exclusion of fire."

The Sawtooth National Forest is proposing to try reversing the trend on the Sawtooth National Recreation Area (SNRA) and Ketchum and Fairfield ranger districts. Forest biologists are drafting an environmental analysis for all three management areas.

"The analysis is being prepared to address aspen decline and includes various methods and alternatives for treatment and regeneration," Bumpus said.

According to the Wood River Watershed Analysis, a Forest Service study on the entire Wood River aquifer, aspen trees cover less than 1 percent of the landscape in the drainage. Historically, according to the study, 10 percent or more of the land was blanketed with aspens.

Aspen trees, according to Sawtooth National Forest biologist Robin Garwood, are a "pioneer species," meaning they grow more vigorously when their root systems or branches are disturbed.

When the West was settled, humans began taming fires, which are the most common natural form of disturbance for aspen trees. Also, humans introduced cattle and sheep to the tasty trees. The animals can chew up little aspens before they grow even a few inches off the ground.

The result of smaller and more limited fires and grazing in aspen country is that coniferous trees are taking over.

"Conifer species are coming in and taking over our larger aspen stands," Garwood said. "You’ll see a lot of Doug fir taking over with small aspens sort of mixed in throughout."

Beyond aesthetics, aspen play an important roll in interdependent ecosystems.

"It’s a desirable species," Garwood said. "There are a lot of wildlife species that use aspen. Elk and deer, particularly, eat young aspen."

Garwood acknowledged that deer and elk, like livestock, can overgraze when their populations are too dense.

The trees also create areas where grasses and shrubs can take root, creating havens for many other animals.

"They add diversity in otherwise similar habitat," Garwood said.

By learning why aspen stands gain more health when subjected to duress, forest managers are helping to stimulate aspen regeneration.

Aspen trees produce two different hormones under opposing circumstances.

One, called auxin, is a growth inhibitor. Auxin is common to mature aspen trees and ensures that other species don’t compete with a tree or stand for nutrients.

Because aspen primarily reproduce through suckers—a biological process whereby new trees grow from an existing tree’s roots—a tree can inhibit the growth of the new tree, called a clone, with auxin flows.

Studies show that disturbance can reduce the flow of auxin.

"Interference with the auxin supply by cutting, burning, girdling or defoliation decreases auxin concentrations in roots. This enables suckers to be initiated or, if their growth was suppressed by auxin, to continue to grow," according to a study by plant physiologist George Schier. Schier works for the Forest Service’s Intermountain Forest and Range Experiment Station in Ogden, Utah.

Schier also points out that aspen trees produce a growth-initiating hormone called cytokinin, which is also produced when trees are disturbed.

"Obviously then sucker production can be promoted by decreasing the concentration of auxin or increasing the concentration of cytokinins," Schier states.

On the Sawtooth National Forest, biologists Garwood and Bumpus have previously worked on ways to promote aspen regeneration.

In the fall of 1998, Forest Service officials authorized projects in Pole, Fourth of July and Champion creeks, in the White Cloud Mountains, in which roots around aspen trees were "ripped" using a tractor.

The idea, Garwood said, was to decrease auxin flows and increase cytokinins to stimulate sucker production.

"We haven’t gotten a huge response," Garwood said. "We got a little suckering around the edges."

When asked if aspens are really phasing out in the West, Garwood answered quickly.

"It’s a long process, but it’s currently happening as we speak. It’s a real problem. I feel it’s urgent, but I don’t know if it’s something we’ll be able to solve in our lifetime."

A short briefing paper describing the "purpose and need" for the environmental assessment is available at Sawtooth National Forest offices in Twin Falls or at the Fairfield, Stanley or SNRA forest offices.

The Forest Service is requesting that written comments be returned by Jan. 15.

 

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