Helena National Forest

Elkhorns Wildlife Management Unit

Elkhorns: Elkhorns and Fire: Aspen Project

Aspen sprouting after a prescribed fire

Slim Sam Aspen Project
by Jodie Canfield, Wildlife Biologist

Here and there among the meadows and dry forests that characterize the Helena National Forest, your eye will be drawn to the refreshing contrast of an aspen stand. Aspen leaves, a lively green in the spring and summer, turn to beautiful shades of yellow and orange as they “quake” in the autumn breezes. Even in the winter, the mottled white aspen trunks stand out.

Aspen stands are full of life and add dramatically to the “bio diversity” of the Helena National Forest. But, take a closer look and you may notice that aspen stands, across the forest, are literally falling apart. Researchers estimate that aspen has declined by 64% in Montana. Why is this and what can be done to keep aspen thriving on the Helena National Forest?

Aspen are a relatively short-lived tree species that reproduce mainly by sprouting. Aspen stands are really “one organism” that require some kind of disturbance to maintain a presence on the landscape. Historically, this disturbance came in the form of large wildfires.

Left without periodic disturbance, aspen clones mature and provide a place where shade-loving conifers can thrive. Because their bark is alive, aspen are inviting to browsing animals, which can scrape the bark with their teeth (or antlers). These “scars” in turn invite disease and insects. Aspen need sunlight and are “picky” in regard to soil temperature (not too warm, not too cold) and soil moisture (not too wet and not too dry). So without disturbance from fire, and in the presence of large browsing animals, aspen are being shaded and eaten to death.

Most of the mature aspen we see in southwest Montana originated around the turn of the century. There are two reasons for this – large fire events and low big game numbers due to market hunting.

In an effort to better understand the dynamics of small aspen stands, the Slim Sam aspen project, located in the southeast portion of the Elkhorn Mountains, was initiated in 1999. The objectives of the project were to inventory all aspen stands in the Slim Sam watershed, to determine what was affecting aspen sprouting and survival, to treat some of the stands with fire or removing conifers, and to measure how aspen responds to various treatments.

Eighteen aspen stands were inventoried. Before treatment, very few sprouts were counted in these aspen stands. On average, there were about 4 live sprouts per 100 square feet. The factors causing stands to decline in the Slim Sam project area included shading from juniper and Douglas fir (conifers), old age, and browsing and mechanical damage from livestock, moose, and elk.

In 2001, crews sawed the conifers that were shading the aspen either to prepare the stand for burning or to use in constructing a “slash” barrier around the aspen stand. Eight stands were burned in the spring of 2002. Because of livestock grazing and abundant elk in the area, six of the burned stands were fenced, with 7-foot high wildlife fencing, in the summer and fall of 2002. In 8 of the 18 stands, conifers were removed and placed around the outside of the stand to provide some protection from browsing animals. Two of the stands were not treated.

To see a graph of the results, click here

The first year following the initial treatments, aspen sprouts were counted again. The results were quite variable, but dramatic! In the stands that were burned, there was about a 35-fold increase. In unburned aspen where conifers were removed, there was a 4-fold increase. Aspen sprouts increased even in stands with no treatment.

Second year results were even more dramatic. Aspen sprouts declined significantly from the first year in all treatment types. What caused this dramatic change? Following fire, there is a tremendous flush in sprouts which naturally thin themselves over time. Also, a closer look at precipitation patterns showed that 2002 rainfall in May and June was 5" compared to 2" in 2003. This might explain why all aspen stands produced sprouts in 2002 compared to 2003. The rest of the story can be attributed to the "ice cream theory". Aspen sprouts are like “ice cream” to many browsing animals. Most of the brush fences did not keep either wildlife or livestock from enjoying a few tasty sprouts. Even the wire and mesh fences had problems. A moose crashed through one fence and deer had pawed holes and crawled underneath other fences. Still, the most dramatic declines were in untreated and unfenced stands. Aspen fences are expensive to construct and maintain, but may mean the difference between life and death of a regenerated aspen stand.

Findings from the Slim Sam aspen project will guide other aspen restoration projects on the Helena National Forest so that future generations can also enjoy golden aspen leaves rustling in an autumn breeze.

To see a more in-depth presentation on this project, click here

Stand treated with fire and fenced to keep out wildlife and livestock

USDA Forest Service - Helena National Forest
Last Modified: Monday, 02 July 2007 at 17:30:17 EDT