Wildfire or logging? The truth about watershed health

Dr. Uldis Silins, a professor of forest hydrology at the University of Alberta, brought more than two decades of field-based research to the Frank Slide Interpretive Centre on June 16, offering an in-depth look at how wildfire and logging impact watershed health in southern Alberta.

In a follow-up interview on Tuesday, June 17, Silins expanded on the research presented the previous evening at the event hosted by the Crowsnest Conservation Society. The long-running Southern Rockies Watershed Project, he explained, has tracked hydrological changes in the region since the 2003 Lost Creek Wildfire, producing some of the most comprehensive data sets on cumulative watershed impacts in the province.

“There are no simple answers,” said Silins. “The effects of disturbance on watersheds vary widely depending on the local geology, climate, land use and the type of disturbance. What happens here in the Crowsnest Pass is very different from what happens in British Columbia or the southwestern U.S.”

Silins began his research in the Crowsnest Pass following the Lost Creek fire, setting up seven small watersheds to monitor the impacts of both fire and salvage logging. Of these, three were burned, two were later logged, and two were kept as undisturbed references. Over an 11-year period, his team studied everything from water quantity and flow timing to nutrient loads and aquatic ecosystem response.

“One of the more striking things we observed was the explosion of algal growth in burned streams,” he said, “These are nutrient-poor mountain rivers. But after the fire, with sediment and phosphorus entering the system, they became hotspots of biological activity almost overnight.”

The fire didn’t just change the chemistry of the water—it transformed the entire food web. Invertebrate populations boomed, which in turn provided more food for fish, altering stream dynamics for years. However, not all impacts were positive. Nutrient spikes such as nitrogen returned to baseline levels within five or six years, but other parameters, including sediment, phosphorus and dissolved organic carbon, showed little to no recovery even after a decade.

Following this, Silins and his collaborators expanded their research to other fire-affected areas, including the 2016 Horse River Fire near Fort McMurray and the 2017 Kenow Fire in Waterton Lakes National Park. These studies reinforced how fire impacts differ from region to region.

“In Colorado, they often see flash flooding and debris flows after fires,” he said. “But in the Alberta Rockies, we don’t get those dramatic floods. What we do get is long-term sedimentation and nutrient loading that persists year after year.”

The difference, he explained, lies in the bedrock. Southern Alberta’s sedimentary geology produces fine silts and clays, and glacial soils retain these sediments in large quantities. When fire removes the vegetative cover, those sediments are mobilised by snowmelt and rain. Unlike regions with granitic or metamorphic bedrock, where soils are thinner and recover faster, the Southern Rockies continue shedding fine sediment for years.

Silins also discussed studies on legacy logging impacts, including harvests from 30 and even 60 years ago in the Upper Oldman River basin. Despite the passage of time, his team was still able to detect hydrological changes in some of those older catchments, highlighting how land-use legacies can linger far longer than expected.

Perhaps the most surprising results came from the Star Creek Logging Study, a government-led initiative that involved three different harvesting methods applied to adjacent sub-catchments; conventional clearcutting, partial cutting, and shelterwood strip harvesting.

With baseline data already in place from earlier wildfire research, the Star Creek site allowed a before-and-after comparison of how each method affected flow and water quality. The results defied expectations.

“We didn’t just fail to detect sediment increases after logging, we actually saw a decrease,” said Silins, “And it wasn’t just in one cut block. It was consistent across all three treatments.”

The reason, he believes, lies in the meticulous application of modern best management practises. Roads were built and decommissioned in the same year. Erosion controls were installed immediately. Disturbed soils were recontoured and stabilized.

“Logging today is not what it was 30 or 40 years ago,” he said, “When done carefully, with attention to erosion control and road rehabilitation, it can be done without significant harm to watershed values.”

While the study was designed to compare impacts across different harvest types, the uniformly positive results meant those comparisons could not be made. Still, Silins said the findings are encouraging.

“It’s a bit of a good news story,” he said, “It shows what’s possible when forestry operations are conducted to the highest standards.”

In both fire and logging studies, one hydrological trend remained consistent: an increase in base flows during dry periods. Trees use a significant amount of water, and when they’re removed, either by fire or harvest, more water enters the subsurface and slowly recharges stream systems.

“These streams are heavily groundwater-supported,” Silins explained, “So after a disturbance, you’re not getting floods, but you are getting more consistent base flows, especially in winter and late summer.”

But Silins stressed that individual events are only part of a much larger picture. In recent years, his team has turned its attention to the entire Crowsnest River sub-basin, measuring flow and water quality from headwaters above Crowsnest Lake down to the confluence with the Oldman River.

“This is one of the most developed and impacted sub-basins in Alberta,” he said, “We’ve got forestry, historic and proposed coal mines, agriculture, growing communities, stormwater runoff, and climate pressures all acting at once.”

Of particular concern this year is water supply. Silins said spring snowpacks were well below normal, and the early melt has left river flows tracking six weeks ahead of schedule.

“The Crowsnest and Upper Oldman are about as low as I’ve ever seen them in June,” he said, “Without significant rainfall, we could be facing serious shortages later this summer.”

The ongoing cumulative effects study will examine everything from selenium loading to the role of wastewater treatment and storm sewer runoff in altering river health. Silins said the findings will be important not only for provincial regulators but for municipalities and residents trying to plan for long-term resilience.

“This work has been going for 22 years,” he said, “And we’re still learning. The more we understand how our activities shape water systems, the better we can manage them.”

Silins offered to provide updated photographs of the Star Creek area and burned watersheds to accompany the story. He said despite the challenges ahead, he remains hopeful that informed decisions, grounded in long-term research, can help protect water resources in the Crowsnest Pass and beyond.