On July 13 2002, lightning storms sparked a series of wildfires in southwest Oregon. The smaller blazes merged and were eventually dubbed the Biscuit Fire.
The fire lasted five months. It consumed 700 square miles from the edge of the California Redwoods to Oregon’s Rogue River. It was one of the largest recorded fires in the Northwest.
Much of land that burned was in the Kalmiopsis Wilderness and the Rogue River Siskiyou National Forest. After a fierce debate over the value of salvage logging and replanting conifer seedlings, the land was largely left to recover, and reforest, on its own.
From trees that can literally resurrect themselves to vanishing soil, here are five surprising lessons ecologists have learned from the Biscuit Fire and recovery.
1. A Mighty Wind
The Biscuit Fire utterly transformed the soils in areas that burned intensely. Bernard Bormann, an ecologist with the Forest Service’s Pacific Northwest Research Station, says all the organic material in the top layer of soil — decomposing leaves and roots, bacteria, microbes — burned up in the fire. When Bormann examined the soil closely he realized about an inch of fine mineral and small rock particles were also missing. And minerals don’t burn.
In a fire like the Biscuit, air speeds can reach up to 100 miles an hour at the surface of the soil. After consulting with fire meteorologists and reviewing satellite images of the fire’s smoky plume, Bormann has hypothesized that the missing soil minerals were swept up into the fire’s plume and carried out over the ocean.
2. Resurrection Trees. Or, Why It Pays To Have a Burl Conifer species like Douglas fir and incense cedar have relatively shallow roots, which are easily killed by fire. Many of them died in the Biscuit. But a few fire-adapted hardwood species — Madrone, Tanoak, and chinquapin — have deep roots that sink into bedrock, and survived the fire even when their branches and trunks burned down.
In addition to deep roots, madrone and tanoak have a hidden, underground woody structure -— a giant tuber, essentially — called a burl.
“It’s a burl that’s full of little hidden buds, called primordia. And they can sprout from thousands of places on this burl,“ Bormann says.
The burls also contain a store of sugar, an energy source. This adaptation meant that madrones were resprouting just weeks after the fire, with a mature root system ready to go.
One more mind-bending fact about hardwood burls: they’re old. Bormann says that based on the growth patterns he observed, some individual madrone trees may be several thousands of years old, and have resurrected themselves on the same site dozens of times.
3. Hardworking Hardwoods Help Rebuild the Soil
Bormann has been measuring soil respiration, the exhalation of carbon dioxide produced by all the living microbes and bacteria in the dirt. His respiration measurements show that 10 years after the fire, about 50 percent of the life in the soil has returned.
That represents a huge loss of life in the forest ecosystem, but also an impressive recovery.
And Hardwood species like madrone and tanoak are proving key to rebuilding the fertility and health of the soil. Their deep roots deploy organic acids to dissolve rock and extract important minerals. The trees use those minerals to build branches and leaves. And when those branches and leaves fall and decompose, nutrients and minerals are added into the soil.
“The soil organic matter is rebuilding after the fire principally due to hardwoods,” Bormann says.
Bormann thinks there is a broader lesson in this: Foresters should consider mixing in or rotating hardwoods with commercial timber species like Douglas fir to help maintain soil fertility.
4. Fire Produces Winners and Losers
Drive into the Kalmiopsis Wilderness, ground zero of the Biscuit Fire, and you will see an entire generation of scorched trees giving way to a new generation. It’s a slow recovery process that will take longer than my human lifespan to play out.
Ecologist Tom Sensenig, also with the Forest Service, likes to say that fires produce winners and losers. In broad strokes, the losers tend to be mature forest species: firs, cedars, spruce and spotted owls. The winners,called early-seral species, make up a long list: manzanita, madrone, wildflowers, butterflies, and elk. Some species, like knobcone pine, can only germinate after a fire. Its seed cones are sealed shut with pitch that melts at 200 degrees Celsius.
However, the real picture is more complicated. A fire as large as the Biscuit burns with variable intensity across numerous microclimates and different forest types.
In some places, the fire stayed on the ground, clearing out underbrush but leaving intact mature and old growth conifers. And in those areas, the underburn has encouraged seedlings from species like Douglas fir and even rare Brewer spruce to sprout.
5. What We Haven’t Learned Yet
In the aftermath of the Biscuit Fire, a public controversy erupted over whether or not to salvage log some of the standing timber in the burn zone. To address the controversy, the Forest Service proposed a large-scale management study, to compare the long-term recovery in stands that were salvage logged and replanted against stands that were left alone. A third study area would have looked at the impact of controlled burning and fuel reduction.
10 years later, lawsuits over the salvage logging, a lack of funding, and the study’s ambitious scale have made it difficult to implement and monitor.
Both Sensenig and Bormann say the Forest Service will release preliminary results from the management study later this year, but neither ecologist is optimistic that the study will have clear results at this point.
What’s more, while both scientists hope the study will yield some useful observations, they say the scaling back of salvage logging and delay in some controlled burning treatments may limit the study’s long-term conclusions.
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