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I’d spent the morning trekking through a typical northern forest woodland of 100-foot maples, oaks, and poplars tightly knit with wild grapevines. The umbrella of trees was shading me from the midday sun when the forest canopy suddenly opened, and I stepped into a sun-filled gap. I squinted in the sun as I tried to decipher the unique scene. Shrubs no higher than my waist
hugged the ground. Unfamiliar grasses blanketed every inch of the opening.
Why had this tiny grassland emerged within such a dense hardwood forest? I looked for clues. There were four snags, bleached corpse-white and perforated with more holes than a sieve, serviceberry, and miniature oaks. Three maples I guessed to be about 25 years old grew on top of each other at one end of the clearing. A wide beech stretched skyward, a few dead leaves flapping in the breeze, a triangular scar on its trunk. An old oak lay on its side, its exposed rings telling stories of drought, monsoon, and fire.
I was in a forest that I guessed had burned 5 years earlier, and some 30 years before that, too. Now the rejuvenated soil was nursing new trees that would eventually tower overhead. How did I know all this history? Every woodland is like a mystery novel waiting to be read, the evidence gathered and analyzed, the enigma unraveled. The culprit in this case, fire, is easy to identify because it leaves such obvious clues blazed into the landscape. Learn to identify and interpret these clues and a forest becomes an open book, ready to reveal a story.
From ground to crown
The effects of a few types of fires will be most obvious to hikers.
Ground fire: Always caused by lightning, ground fires burn beneath the duff, so you won’t see flames. Keen observation is needed to uncover traces of this kind of burn. Ground fires char mosses and some roots, but rarely harm living plants taller than your ankle.
Surface fire: Caused by controlled burns or unextinguished campfires, surface blazes creep across the land and consume leaf litter and downed branches. These fires actually promote life by baking open sealed cones (called serotinous cones) of ponderosa, lodgepole, jack, and pitch pine, as well as the seedpods of buck-brush, manzanita, golden eardrops, whispering bells, and mountain balm. Once the seeds drop, reproduction begins. A multitude of these fire-dependent plants in one area indicates a recent fire.
Crown fire: With ambient temperatures as high as 20,000°F (almost 95 times the temperature at which water boils), these fires incinerate everything—dead and living plants, seeds, minerals, even soil bacteria. The resulting dark, solidified soil grows nothing for years.
THE DAY AFTER
Immediately after a fire, it may seem that no burning questions about its cause and effect exist. The local newspaper and rangers will already have stated the facts. The sharp observer can glean more information from the scene, however. For instance, inspection of a tree’s charred remains can reveal the state it was in when it burned.
- Dead trees leave behind shiny black, cobblestonelike charcoal.
- Living trees become a dull black charcoal.
- Standing dead trees generally burn completely and quickly. There’s often nothing left but a 1- or 2-foot snag sticking out of the ground. You can also deduce which way the fire traveled across the land.
- Windblown flames can carve odd shapes into the windward side of a dead tree, creating a “totem tree.”
- Trees blackened on one side but only slightly charred on the other are known as “two tones.” These trees were alive and healthy at the time of the fire, and the side of the tree that’s blackened faced downwind.
THE DECADES AFTER
Years later, you can still decipher when fire last hit an area. The easiest way is by observing the flora and fauna that returned. As blazes level tall trees and undergrowth, holes are left in the forest canopy, “so all of a sudden you have sunlight hitting the forest floor,” explains Jack Cohen, Ph.D., a fire physicist at the Intermountain Fire Research Laboratory in Missoula, Montana. “This produces a profusion of shrubs, flowers, and shade-intolerant plants like fireweed, and the soil in these areas is rejuvenated. More insects come in, as do animals that forage on the plants and bugs. This brings in the predators, like wolves and bears, to prey on ungulates.”
Other signs of a past fire:
- A basal scar, or triangular score on a tree trunk often is the result of a surface fire that didn’t kill the tree. The taller the scar, the faster the fire that moved through the area, says Ronald Wakimoto, Ph.D., of the University of Montana School of Forestry.
- Trees with multiple trunks can result if the trunk was destroyed by fire but the rootstock wasn’t, according to Tom Wessels, author of Reading the Forested Landscape. Called rhizomes, these roots produce numerous shoots that ensure the survival of the plant. Many of the new shoots die or nourish deer and other browsers, but occasionally two or more adjacent seedlings survive and grow in tandem. The height of these sprouts indicates how long ago the fire occurred.
You can guess how often fire occurs in an area by looking at the vegetation. Trees in frequent fire areas (a fire cycle of 20 years or less) grow thick bark to resist heat, and they also self-prune, or drop their lower branches. Douglas firs, ponderosa pines, and redwoods fit this description. When fire sweeps through, the downed wood, rather than living trees, is consumed.
In areas of infrequent fires (a 70- to 400-year fire cycle), the trees aren’t as well adapted to flames. They have thin bark and their bottom branches usually remain intact even when dead. Fire quickly burns up this “ladder” of branches and sets the crown of the tree alight. Subalpine firs and Engelmann spruces generally indicate areas of longer fire cycles.
Even with all this fire knowledge, you can be misled easily by the many variables in nature. “There are no rules, only general principles (in fire succession), and there are exceptions to every principle,” cautions Dr. Cohen.
Still, you should now be able to decipher a forest well enough to understand your surroundings, and in the end, that’s what makes a hike most fascinating and memorable.
Steven Hawley assisted with this article.
Online Extra: Firewalking
Some 84,000 fires blazed through the West during the summer of 2000. Does that mean all the great hiking spots west of the Mississippi went up in smoke? Hardly. Plenty of destinations were untouched. Those that were kissed by flames offer a peek at an ancient cycle older than man and a fundamental truth of nature: Destruction breeds rebirth. Follow one backpacker who rediscovered a landscape he thought he knew. Then check out seven hikes that’ll take you to the heart of last summer’s flash points.