Yellowstone National Park's Cache Creek burn area
Image Credit: Bill Schaefer, Idaho State Journal

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ISU stream ecologists find resurgent stream life amid the ashes of '88

One sunny day last August, stream ecologist Colden Baxter stood on the rocky banks of Cache Creek deep in the wilds of Yellowstone National Park, where he and other scientists were studying the effects of the wildfires of 1988.

Baxter, director of Idaho State University's Stream Ecology Center, was encouraged by what the research expedition was finding amid mountains and meadows where charred pines still stand.

"Things are not degraded here at all," the Montana native said. "In general, the stream is coming back in a way that was predictable and expected."

During the summer of 1988, fires of epic proportions swept across 1.2 million acres of the Yellowstone region, including about 793,000 acres in Yellowstone National Park. News accounts at the time depicted devastation.

Two decades later, however, ecologists are finding positive impacts of wildfire, impacts that support the idea that wildfire is an important process of a natural ecosystem.

Idaho State University stream ecologists began studying the Yellowstone fires literally while the embers still glowed. During the event's 20th anniversary last summer, an ISU team returned to the park after a long absence. They spent 12 days in the wild, revisiting sites they'd not seen in years.

What they found was not the ruin that some news accounts, written from the front lines in the heat of the moment, seemed to convey. Instead, they found evidence that the ecological systems of streams like Cache Creek are, by some measures, more productive than before the fires.

Baxter, Ph.D., and renowned ISU stream ecologist Wayne Minshall, Ph.D., now professor emeritus of biological sciences and the founder of the Stream Ecology Center, led last summer's scientific journey into the legacy of fire.

They were joined by former students, current students and some ISU biological sciences seasonal workers who headed into the backcountry for seven days to Cache Creek, a tributary of the Lamar River in the northeast corner of the park. They then spent five days studying sites closer to the park's road system.

Few places in the park burned more completely than did the upper portion of the Cache Creek drainage; about 80 percent was charred. On lower Cache Creek, less than 50 percent of the drainage burned. This entire drainage is an excellent area to study the effects of wildfire and the ability of nature to heal itself. The contrasts between the two areas offer fodder for the researchers to make comparisons on the effect of wildlife in relation to total burn area.

"The most important thing to note is that, until we began our studies, nobody had documented the longterm effects on wildlife and collected data to evaluate it," Minshall said. "It was just all speculation, a lot of it, in terms of the destruction that fire causes, the slow recovery, how it damages the ecosystem and stuff like that. What we've shown is that there is considerable recovery soon after the fire and, at the 20-year mark, that recovery is occurring in a dynamic with the landscape."

For the first five years following the fires, Minshall and other ISU faculty, graduate students, undergraduate students and volunteers studied a number of sites in the park each year. Then, over the next five years, they studied Cache Creek sites annually, and visited other sites irregularly, before studying the bulk of the sites again in 1998. That was the last year they visited the majority of the sites.

"Whatever is done here is new ground, a new piece of the puzzle because no one else has obtained longterm data sets on this type of a natural disturbance," said Minshall, part of the field team last summer. "This will give us the opportunity to reflect on the last 20 years, to confirm changes we predicted, and discover unexpected things."

The most striking and obvious feature the researchers found at Cache Creek was how many of the partially burned trees from 1988 had fallen.

"We were struck by the amount of wood that has fallen down into and across the stream that is both potentially and already providing a lot of habitat," Minshall said. "We expected it, but it was still striking to see. In some places 95 percent of the burned timber had fallen over, is lying on the ground or in the stream. This provides a lot of cover for the stream itself, and on the land it stabilizes the soil."

Although trees and shrubs have reseeded and are growing back again in the Cache Creek drainage, they're not coming back as quickly or growing as fast as the researchers expected.

Still, the health of the stream is robust.

Minshall's studies have focused on the status of the aquatic organisms in the streams, checking which species are present and their abundance. He focuses on bottom-dwelling invertebrates, including various insect species that spend a large portion of their lifecycle in the stream. These little critters, and what sustains them, are a big window through which to view the health of a stream.

What ISU researchers found last summer was that the two major food sources for these aquatic organisms, algae and leaf litter, were in high supply.

"There's plenty of sunlight, a lot of nutrients and the algae are doing well," Minshall said. "At the same time, the riparian plants are coming back and contributing more quantities of leaves. This benefits the fast-growing organisms, such as the insects and the fish—in this case native cutthroat trout—that feed on them."

Cache Creek is now more productive for creek-dwelling organisms than it was prior to the fires, the scientists say.

Baxter said he has found that, several years after the fire, severely burned watersheds also supported a higher density of fly-catching birds, bats, and riparian spiders, among other species.

Minshall and Baxter are quick to note that the fire studies in Yellowstone are occurring in a pristine, natural environment. In a less natural environment, they say, recovery would most likely be much different.

For example, the fallen logs that are now providing streambed habitat and erosion control on the slopes of Yellowstone might have been cleared away in a less-protected environment. In a setting where roads exist, they might have increased the negative effects of post-fire erosion.

"Revisiting the park has fortified in our minds that you have to have a natural reference base like Yellowstone from which to work, to compare it to areas where humans have had a more dramatic effect on the land," Minshall said. "Without that, you can't really appreciate how much we've done to upset natural balances. Yellowstone provides that vantage point."

And from that vantage point, ISU researchers have collected valuable data that has many applications.

"No matter what we find—whether our predictions hold true or are disproved—we further the knowledge on this topic," Minshall said. "And the power of these long-term data sets is that they can be used to make predictions on future events. The power of long-term data sets cannot be overstated."

Andy Taylor
ISU Magazine