California Sketches: How forests recover from fire

08/24/2014 12:00 AM

08/23/2014 8:39 PM

After the Rim fire devastated more than 250,000 acres of the Sierra Nevada and part of Yosemite National Park last year, I wondered how forests recover from catastrophic fire and what the process looks like.

One answer can be found in an experimental research forest east of Sonora near Yosemite, in an area that hasn’t experienced a fire since 1889. An ecologist discovered old research maps that led to an experiment on how forests best recover from fire and what creates a more resilient forest.

Eight years ago, Eric Knapp, an ecologist with the U.S. Forest Service, discovered 1929 research maps in a dusty cupboard in his office. As if on a treasure hunt, he searched the National Archives and found corresponding records in old leather-bound ledgers. He followed the maps into the Stanislaus-Tuolumne National Forest to the original research sites. He found identification tags still nailed to tree trunks. Knapp remapped each site to compare how the forest had changed over 85 years – from soil to shrubs to trees and to the forest canopy.

Knapp and his student assistants established new research sites adjacent to the old, preserved experimental forest. They performed prescribed burns last fall. By comparing two main management concepts, they are documenting new growth and wildlife in the two new experimental areas. In one, they thinned the forest so there was variable spacing, with trees grouped together and open spaces, mimicking how a forest grows naturally. In the second, they cut trees in an even pattern, as is often found where trees have been harvested.

Knapp sends me into the burned experimental areas with his assistants. As we move softly over hot, dusty soil, ash poofs into the air with each step. One raven calls and several bright orange butterflies provide the only excitement in this hushed place.

Bark looks and feels like burned popcorn. Ominous holes pit the forest floor, evidence of where mighty cedar, oak, fir and pine trees once stood. The ground is deceptive. I’m warned to avoid areas where fire has devoured trunks and followed roots into the earth, leaving treacherous voids just under the surface.

Twenty months after the prescribed burns, I can clearly see the difference between the two experiments. In the first, variable spacing allows sunlight to reach the forest floor. Lilac seeds that can hide in soil for a hundred years have been liberated, sprouting green shoots from barren soil. Green oak leaves sprout from stumps.

In the second experiment, shade from the forest has prevented new growth. I touch the remnants of a pine bough, brittle, sharp and dangerous. The green canopy above that survived the fire provides the only vibrant color in this landscape.

Knapp is optimistic but says, “We don’t manage for short-term conclusions, but for long-term. Maybe in five years, we’ll have answers.”

The Rim fire is a landscape of extremes. Patchy forest and meadows are flourishing with grasses, lupine, lilies and tree seedlings. Vastly scorched areas, sterilized of life-producing plants, must depend on man and the wind. Or take another 150 years to recover.

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