If you want to know about a fire that burned in the Sangre de Cristo Mountains a thousand years ago, chances are that a bristlecone pine tree that can tell you all about it.
“Here in the Southwest, New Mexico and Arizona, pine forests are growing in dry, rocky landscape and they get to be really old – up to 1,000 years old lying on the ground,” said Tom Swetnam, former director of the Laboratory of Tree-Ring Research at the University of Arizona.
“There are probably some living trees, bristlecones up in the Sangre de Cristos, that are a thousand years old.”
Swetnam is part of a team of tree-ring researchers working on a long-term study of fire history in the forests near Taos in an effort to chart a course for better fire management in the future.
The idea is to use thinning to restore forests to some semblance of the shape they were in when fires burned naturally, before people started messing with things better left alone.
The trees remember how it used to be.
Using chain saws, researchers cut cross sections out of dead trees or employ a coring process to extract pencil-shaped sections from living trees.
Then, by analyzing burn scars, the cooked resin between tree rings, they can determine when a fire burned, how big it burned and how hot it burned. Even if that fire blazed hundreds of years before Smokey Bear was a cub in the Capitan Mountains.
“For the most part, pine – ponderosa and white – have better fire scar records,” said Ellis Margolis, a research ecologist with the U.S. Geological Survey and part of the Taos fire-history team. “These trees have evolved so that they have characteristics – thicker bark – that survive fires. We look for pines that have survived five, to 10 to 15 fires.”
Besides Swetnam and Margolis, other members of the team include Craig Allen, also a USGS research ecologist, and Lane Johnson of the National Park Service who heads up the project’s field team.
Margolis said that the Taos study cranked up about six months ago and that field work started in June. It focuses on the forests in the Rio Hondo, Rio de Pueblo de Taos and Rio Fernando watersheds.
“I’m not sure just how many acres that adds up to, but it’s a lot of country,” he said.
The project is a collaboration between the Nature Conservancy, an environmental organization, and the USGS.
Tracey Stone, a Nature Conservancy spokeswoman, said the study is part of the conservancy’s Rio Grande Water Fund program, which uses private and public funding to enhance forest thinning. Stone said the Taos Ski Valley Foundation provided the water fund with a $125,000 grant and that, combined with $115,000 in federal and local money, is paying for the fire-history survey.
The goal of the study is to determine what areas of the forests were historically the targets of healthy fires, those low-intensity fires that consumed debris and seedlings, thinning out woods naturally without killing off mature trees.
“If you find trees that have five, six, eight fire scars on them, you know they were in low-severity fire areas,” Margolis said. “You thin out those areas. Those are the areas that have changed the most because we have all those young trees that were waiting for fires to kill them out. But those fires did not come, and the place filled in and got really thick.”
Why didn’t the fires come?
“Sheep,” Margolis said. “Sheep ate all the grass.”
The arrival of the railroad in New Mexico in the late 1870s spurred settlement of the territory and with settlement came livestock, lots of livestock.
Swetnam said there were 5 million to 6 million sheep, cattle and horses in New Mexico by 1900.
He said sheep in the high country grazed down the grasses, the fine fuels that used to feed those low-intensity fires. And the gaps in the terrain created by herds of sheep being driven back and forth to water every day made very effective firebreaks.
“That’s when we see the first decrease in burning,” Swetnam said. “After World War I, the Forest Service cut back on the grazing. But that’s when fire-prevention efforts started.”
As a result, forests that were once relatively sparse grew dangerously dense. When fires started in these choked sections, they burned hot and high, destroying most things in their path and setting the stage for floods that sent ash and sediment into rivers and reservoirs, tainting precious drinking water supplies.
But the trees that might feed a catastrophic fire tomorrow also hold the clues to preventing them in years to come.
“New Mexico is such a rich cultural and ecological landscape,” said Swetnam, who was born in Ruidoso, the son of a ranger working in the Lincoln National Forest. “There are lots of examples of Pueblo and Hispanic people living in these (forest) areas without catastrophic fires burning up their pueblos or villages.”
Swetnam, who now makes his home in the pine forest north of Jemez Springs, hopes it is possible to return to those days when people lived more in harmony with the forest and the fires that burned in them, a time when fires maintained a more stable situation.