Trees on fire with title

The lab is littered with stumps. Matt Beaty heaves one onto the counter and runs his fingers along its severed edge and over its rough-hewn surface, where its autobiography has been written in the language of tree rings. Luckily for Beaty, he's fluent in Tree Ring. He knows the grammar of ring width, the syntax of discoloration, and the context clues of scar patterns that tell the story of one tree's life—and the scenes that interest him most are those in which the tree was injured: forest fire.

Beaty, a graduate student in Penn State's physical geography program, has spent the last two summers expanding and improving his library of stumps. He and a varying troop of undergraduates join their adviser, Alan Taylor, an associate professor of geography at Penn State, on trips to the Lake Tahoe Basin in northern California. Taylor is studying the impact of fire on forest health. The stumps provide the "when, where, and how of forest fire."

Beaty identifies his current sample as a Jeffrey pine by its thick covering of reddish bark, which protects the sensitive growth tissue inside. The outermost ring, the cambium, a thin band of cells between the bark and the wood of the tree, is the only part of the tree stem that is actually "alive." When part of the cambium is damaged by fire, a discolored scar forms. If the cambium is only slightly damaged, new rings can form and begin to heal the scar. If the burn is too severe, the tree will die.

Beaty indicates a hollowed-out section on one side of the stump, where most of the scarring is evident. The cambium is most vulnerable on the uphill side of the tree, he explains. Small twigs, dry leaves, and other debris are halted in their downslope path and build up a fuel source against the trunk of the tree. During a fire this fuel store will smolder and eat away at the bark of the tree, wounding the inner cambium.

"Remarkable," Beaty murmurs under his breath. He points toward the center of the stump, at the first ring of discolored wood that represents a fire scar, a ring the diameter of a hockey puck. "This tree was very young when it survived that first fire." In California's temperate climate a tree produces one growth ring per year, so a quick tally yields the age of the tree when it was scarred by fire. It can be trickier, though, to determine the calendar year in which the fire occurred.

"It's helpful if the bark is intact on the sample," Beaty confides. "Then you know you have the outer wood. The outer year should correspond to the year the tree was cut or logged, and we count backwards from there. This gives us a starting point, but we never know the outer year of ring formation. We cross-date all samples using marker years." Beaty refers to a sheet of paper bearing a complex table of dates, dashes, and codes indicating the average ring-width for each year. "Marker years are years that were either uncommonly wet or uncommonly dry. Wet years yield wider rings, while dry ones are much narrower."

Beaty slides the six-inch cross-section of Jeffrey pine under a microscope, grabs a nearby pencil, and peers through the lens. He counts nine rings from the bark and marks a small "x" on the wood. "There, that's 1990," he declares and proceeds to cross-date the stump, marking every tenth band. "See those two narrow rings, right at 1960 and 1961? Those are marker years." He gestures toward the pile of stumps towering behind him. "Almost all of these stumps will have those same narrow rings."

After a tree has been cross-dated, it is easy to pinpoint when a particular fire occurred. Gazing through his microscope at the alternating light and dark bands, Beaty can determine, not only the year of scarring, but also the season. Each ring is made up of lighter wood that formed early during the growing season and the outer, darker wood that formed during California's dormant season in the fall. "If a scar interrupts the lighter wood, then the fire occurred during the spring or early summer. If the scar forms after the dark wood, then the fire happened after the tree stopped growth for the year."

The job of scouring the forest, searching for stumps to add to the collection, fell to the undergraduate members of the team. "Stump-hunting" was Jeff Balmat's favorite duty, when he joined the Lake Tahoe project in 1998. Balmat, who majors in geography, loved "roaming around the forest looking for clues about the past," he says. And, according to the stumps, the Tahoe of the present is not the same as the Tahoe of the past.

Most of the stumps were cut when silver fever swept Nevada and California during the Comstock Lode Era of the 1860s and '70s. Entire stands of trees were logged and leveled. Now the oldest living trees in the Lake Tahoe Basin are mostly 100-120 years old; there are no remaining old-growth forests. Yet the stumps have carefully preserved a record of the forest's history. Mapping and inventorying the stumps yields a picture of how the forest used to look before it was changed so drastically by large-scale logging. Resource managers and ecologists like Taylor use this picture to evaluate how humans have altered the landscape.

Humans had a huge impact on forest structure when they introduced fire suppression as a forest management practice in the early 1900s. Fires were suppressed to prevent what was viewed as the destruction of a lucrative resource: the 2.5-foot wide pines felled to support the burgeoning population of people working in these rich silver mines. Yet, without frequent low-intensity burns, the accumulation of fuels could lead to more severe fires. Dead branches sway from treetops and act as ladder fuels, providing the fire easy access to the crown of the trees where leaves burn easily. Crown fires spread quickly and are much more destructive than surface fires.

rings of tree stump

Fire had previously acted as a disturbance agent, stirring up the ecosystem and setting the stage for change. Whether it burns for a few seconds or rages for months, fire leaves its mark upon the landscape: depositing mineral elements and stripping away the top organic layer of soil. Some trees will die; others will scar and survive like old warriors. As the ecosystem shifts, conditions may favor new species. Perhaps a severe fire destroys a leafy canopy, reducing a lush forest to a brush field. "It takes time for the forest to come back," Taylor explains. "And the returning trees may or may not be the same species that burned. Fire effects are very diverse, and this diversity promotes biological diversity."

Many trees depend on fire for their survival. Some types of conifer have developed cones that need the heat from fires to release their seeds. In areas of Tahoe where pine dominates, frequent, light surface fires previously killed most of the seedlings and saplings in the forest understory. Those that survived grew large and old without the pressure of competition from neighboring trees. Without fire checking their encroachment, new species, such as the shade-tolerant firs, are free to invade the pines' territory. The composition of the forest has changed significantly since the 1800s. Pioneers could no longer drive their covered wagons between the trees through the open spaces of the forest. The forest today is much denser, and the individual trees are much smaller.

stretched out tree ring
Matt Beaty

Balmat and the other student geographers identified the current forest composition by inventorying the types of trees and their physical characteristics. The forest was divided into plots 100 meters by 50 meters in size. The students mapped the location of every tree and recorded its species, height class, and diameter. To undergraduate Jeff Rubini the trees they mapped were more than just impersonal entries in an inventory. Rubini, who worked with Taylor and Beaty in the summer of 1999, had his own classification scheme: the Jeffrey bark and strong scent of vanilla and caramel; the fuzzy bark of the fine-grained cedar; the tall toothpick-like trunk of the lodgepole pine with its hat of needled branches and dark bark; the foot-long cones of the sugar pine; and the red and white firs that look like Christmas trees, distinguishable only by the presence of either red inner bark or white-striped needles.

But working in the forests of Tahoe was no summer vacation: It was hard work. The students' most rigorous duty was coring, or obtaining random samples of live trees from each plot. Pete DeLuca, who joined the project as a junior in geography in 1996, mastered the art of wielding an increment bore, a metal tube with a bit on the end that is screwed into the tree to extract a pencil-sized sample. The cores are transferred into a drinking straw for storage and sent back to the Tree Ring Lab at Penn State, where they are cross-dated and analyzed in much the same way as the stumps. "Coring was hard work on some of those trees, especially on a steep slope." Trees that grow on a steep hill are cored on the uphill side because they have more wood on the downhill side. "It was a good workout. I was in the best shape of my life," DeLuca says.

Despite the demanding nature of the work, or perhaps because of it, DeLuca, who now works for an environmental engineering firm in Virginia, learned what he refers to as "invaluable lessons I still use today." DeLuca uses the same field techniques he learned from Taylor in his present work, mapping the floodplains of states east of the Mississippi River. "Alan definitely trained me to be knowledgeable in the field, quick thinking, and able to work under extreme environmental conditions."

No matter how long the day, DeLuca knew he could always look to Taylor for inspiration. "He never slows down," DeLuca says. "He wears a bright orange vest and a crazy hat like Indiana Jones. We'd be struggling to climb up a hill, meanwhile Alan's already at the top. He never really lifts his feet off the ground. He just glides right over twigs and sticks."

For Taylor and Beaty, one of the joys of bringing undergraduate assistants into the project is witnessing the obvious awe in the faces of Eastern students unfamiliar with the wide-open landscapes of the West. Indeed, to Balmat, a native of Pennsylvania, working in the forests of Tahoe was like "studying abroad in a country that doesn't speak your native tongue." He explains in an e-mail message from New Zealand, where he spent last spring semester, "Growing up in the woods of the Appalachians, the flora of the Sierra Nevada range was completely new, but soon you recognize the smell of Jeffrey pine and learn to avoid painful thickets of manzanita." Manzanita, Balmat explains, is a bushy shrub whose branches are bendable but stiff, so that when you walk through it, you get scrapes on bare skin. "Sometimes," he adds, "we would have to wade though patches of manzanita, and it wasn't all that fun."

To burn or not to burn remains a hot topic among ecologists and resource managers, Taylor explains. "If you work with forests and fire, you can't not talk about resource management. Both components are there. That's what's fun about it," he claims. Perched upon a swivel chair with his wooly socks peeking out from a pair of Birkenstock sandals, Taylor propels himself across the office floor to his file cabinet. He pulls out a newspaper article. The headline screams, "$50 million for Lake Tahoe, a troubled treasure." Below the headline, a triumphant President Clinton raises two fists in a victory stance. Taylor explains, "Our funding comes from the USDA Forest Service through President Clinton's 1997 environmental forum for Lake Tahoe."

four researchers sit at base of giant tree

The President's support is evidence of widespread interest in how the Lake Tahoe Basin is managed. In 1992, the Forest Health Consensus Group (FHCG), whose members come from federal, state, and local governments; environmental organizations; private business; academia; and the general public, was formed in response to the public's perceived threat of wildfire. The group's goals are to protect Lake Tahoe forests, private property, and human lives. As Taylor explains, "The Forest Service tried to include a lot of people in the decision-making process. But the more people you invite to a party—the party can get out of hand pretty quick. It's complicated. Different people have different definitions of 'forest health.' It's like a little microcosm of how people and fire and ecology get tangled up in one place."

Taylor's part is to help people involved in conservation decide what kind of forest they want to maintain. "I can't define 'forest health,'" Taylor explains. "I am identifying a reference condition, and we assume that forests were more resilient then than now." In response to his findings, a limited program of prescribed burns began in the basin two years ago. These human-ignited fires are carefully supervised and kept under close control.

To help educate the public on management issues, Taylor has created a Web site called "Lands in Transition" that explains the many different perspectives that must be considered in managing the forest. Visitors to the Web site can play the role of a forest manager, entrusted to maintain forests that are resilient and resistant to changing environmental conditions. "The really neat thing about it," Taylor says, clicking his mouse as he navigates through the site, "is that you can consult with experts to make your management choices. Then you can see the results of your choice.

"Let's talk to Phil," Taylor suggests. Phil Weatherspoon, an authority on forest health at the Pacific Southwest Research Station in the Redding Silviculture Laboratory, appears in digital video and warns that, although light burning generally improves the vigor of trees, it could increase their susceptibility to bark beetle attack. Phil is one of a panel of five advisers, experts in fire ecology, forest health, atmospheric chemistry, soil and water science, and resource management, who help the viewer make wise choices—a difficult thing to do, according to Taylor.

"If you choose to implement fire and selective logging to thin the dense forest, yes, the trees will be healthier, but your actions may have a negative impact on air and water quality. Burning releases chemicals into the atmosphere and bares the soil, inviting erosion and sediment deposit into streams and ultimately into Lake Tahoe.

"There's no right answer to forest management. People may agree on what they want, but they can't agree on how to get there. It's a value-laden process filled with uncertainty. Forest managers at Tahoe are making decisions with imperfect information, but given our state of knowledge, they're doing the best they can."

Jeffrey Balmat and Jeff Rubini are geography majors in the College of Earth and Mineral Sciences. Peter DeLuca graduated in May 1998 with a B.S. in geography. Alan Taylor, Ph.D. is associate professor, 302 Walker Bldg., University Park, PA 16802; 814-865-3433; Matt Beaty is a doctoral candidate in geography; 302 Walker Bldg.; 865-3433; Taylor's work is funded by the USDA Forest Service. The CAUSE program (Center for Advanced Undergraduate Study in the College of Earth and Mineral Sciences) provides travel support for undergraduates. Taylor's Web site, Lands in Transition, can be found at Writer Anne Beausang will graduate in May 2001 with a B.S. in geography.

Last Updated September 01, 2000