Gondola fire provides clues to researchers: Scientists find prescribed burns best to decrease nutrient flow into Lake Tahoe

A wildfire that destroyed 673 acres of forest three years ago under Heavenly's gondola is helping researchers understand how a fire's intensity affects the amount of algae-feeding nutrients flowing into Lake Tahoe.

High-intensity wildfires produce the most nutrients in runoff, scientists believe, while low-intensity prescribed burns actually decrease the nutrients washed away from the land.

Nutrients such as phosphorous and nitrogen account for about half the lake's loss of clarity by encouraging algae growth. Some of these nutrients come from fertilizers golf courses and home owners use on their lawns.

Since algae needs both nutrients to grow, the Tahoe Regional Planning Agency is encouraging companies and residents to choose "zero phosphorous" fertilizers, creating a phosphorous-limited system in the lake.

But nitrogen and phosphorous exist naturally in Tahoe's soils as well. As fires have been suppressed over decades, those nutrients have been building to high levels.

But when an intense wildfire comes through an area, it releases nutrients in even higher numbers than in an unburned area, said Wally Miller, a soil scientist with the University of Nevada, Reno.

Miller had set up runoff collectors in the area of the Gondola fire before it happened, intending to study nutrients in runoff before and after prescribed burns. But when an actual wildfire raged through the area, he ended up with three sets of data: for unburned areas, wildfire burned areas, and prescribed fire burned areas.

While the study is not complete and he has not made a concrete conclusion yet, Miller said his numbers are starting to indicate the most nutrients are released after a high-intensity wildfire.

Prescribed fires release the least amount of nutrients, even less than an unburned area, Miller contends.

"It's looking like the best way to decrease the nutrient load in the runoff is prescribed fires or mechanical treatment," he said.

Prescribed fires are intentionally set by land management agencies like the U.S. Forest Service. While initially unpopular, public support for intentional fires has grown in the past few years, said Forest Service spokesman Rex Norman.

"Throughout the West, we are finding a great deal more of not only support, but encouragement from communities to get work done," Norman said.

"It was very difficult to get any kind of work done just three or four years ago. People either didn't want the smoke or didn't want the trucks or the crews going through the neighborhood," he said.

The Forest Service studies have also found a connection between nutrients and fire.

"We've found the intensity of the fire has a great deal to do with the type of algae-feeding nutrients that get released," Norman said.

There are two stages to controlled burns. The first is to gather the smaller debris into piles. Small trees, branches and forest debris contribute to the heat of an uncontrolled fire and provide a ladder for the fire to climb to the tree canopy.

Piles provide a controlled way to burn the smaller debris. The piles sit to season for a couple of years to decrease smoke when they are burned. Unhealthy trees are also eliminated in this stage.

The second stage is landscape burning, a controlled low-intensity burn which slowly creeps across the land, opening areas to new growth.

Low-intensity fire was the biggest architect of the Sierra Nevada's ecosystem, experts believe, and some trees depend on fire to open sunny areas for their seeds to germinate.

After decades of fire suppression, Western forests are now unhealthy, with too many trees competing for limited water, thereby becoming susceptible to beetle infestation and intense wildfires.

Agencies like the Forest Service and National Park Service have been applying a more hands-on approach to managing forest ecosystems which, although untouched by man for decades, are now far different from their historically natural states due to lack of fire.