SANTA FE, N.M. — Their boss says trees are “libraries,” serving to document and archive the ecological history of the areas where they grew.
And Collin Haffey and Ellis Margolis have already shelved quite a few slices of tree trunks at a new tree ring laboratory, which formally opened last month in a corner of the Bureau of Land Management building in Santa Fe.
Margolis grabs one sample and explains what can be learned from that nearly perfectly round piece of ponderosa pine found at Chaco Canyon. It tells part of the story of the ancient pueblo people who lived in that part of northwest New Mexico for several centuries before a 50-year drought, beginning about 1130, apparently caused them to abandon the area.
“They built their houses with wood, just like we do today,” he says, showing the sample of what was once a ceiling beam. “So we can tell that this was cut in 1045 … and maybe they added a room in 1052.”
This is what can be learned by reading between the lines of those tree rings, each one representing a year of growth. They tell a story, and it’s Haffey and Margolis’ job is to translate it, not only for archeologists interested in learning about the past, but also for land managers looking ahead to the future.
Reading between the lines
The scientific method of analyzing tree ring patterns is called dendrochronology, and the tree ring lab in Santa Fe, which is actually called the Jemez Mountain Field Station, is the latest advance in a growing field of study that is becoming more relevant during this time of climate change.
The roots of dendrochronology date at least as far back as the 15th century.
“Da Vinci noticed variability in tree rings and that climate determined how trees grow,” Margolis says. “There’s a climate record in tree rings. The power in that is, with climate change, now you can show change compared to what.”
Generally, wider spaces between the rings reflect years of good moisture, while narrow spaces represent dry years. The patterns become recognizable almost at a glance to a trained eye. With near certainty, Margolis can pick out 1748 on some trees because he recognizes the pattern surrounding that year.
“You know 1748 will be small. That was a damn dry year in New Mexico and Arizona,” he says.
By collecting samples from trees whose life spans overlapped, the researchers are able to piece together a chronology of wet and dry years, and everything in between, dating back centuries. “It’s basically pattern matching,” he says of the process known as cross dating. An untested sample is held up against a known one until the patterns match. “The pattern helps with dating and is linked to what we can learn about climate.”
Lane Johnson, a data analyst with the National Park Service, is performing a lot of the cross dating now. He puts the sliced stumps, called “cookies” by the researchers, under a microscope and attempts to match tree ring patterns against other samples taken from the Santa Fe National Forest.
Ultimately, the goal is to track the histories of the forests in the Jemez and Sangre de Cristo mountains, and chronicle fire records for each watershed.
In the Jemez Mountains, the group is expanding on 30 years of work conducted by prior researchers, among them Tom Swetnam, a Jemez Springs native who headed a ground-breaking tree lab in Tucson for many years, and their current boss, Craig Allen, who is based at Bandelier National Monument.
Some of the groundbreaking tree ring research was conducted in the mid 1950’s by Florence Hawley Ellis, who taught at the University of New Mexico from 1934 to 1971.
“One of the cool things about all this is it’s built on an accumulation of work by researchers,” Haffey said.
Finding answers for land managers
Dendrochronology grew out of the forests of the Southwest.
In 1937, Andrew Douglass, who recognized that trees from the same region developed near-exact tree ring patterns and whose research was able to precisely date some of the Southwest’s Anasazi ruins, founded the Laboratory of Tree Ring Research at the University of Arizona in Tucson. It has turned into a pipeline for dendrochronologists, whose science has grown to include the application of tree-ring analysis to ecological questions.
Margolis, a U of A graduate, and Haffey, who attended Northern Arizona University, work for the U.S. Geological Survey. Their field station is an offshoot of the USGS’s Fort Collins Science Center.
“Our stuff is basic, first principles of ecological science,” said Haffey. “We ask, ‘What is the history here?’ and we take that and work with our land management partners … . This science is playing a significant role in helping land managers achieve their goals.”
Haffey says they share their work with such groups as the National Park Service, the U.S. Forest Service, the Bureau of Land Management, Los Alamos National Laboratory, local pueblos, the city of Santa Fe and others.
Their analysis of tree rings provides temperature and rainfall patterns, insect outbreaks and the structural composition of forests to provide a perspective for today’s issues.
“Trees don’t lie. The data is tangible and direct,” Haffey said.
Alan Hook, a water resources analyst for the city of Santa Fe, said some of Margolis’ work in the Santa Fe watershed has been invaluable.
“Ellis’ work really helped us with the vegetation component within the Santa Fe municipal watershed plan, which is a 20-year plan put together by the city, the U.S. Forest Service, the watershed association and the Nature Conservancy,” Hook said, adding that the plan is used to guide vegetation management, water management, outreach and education.
Margolis was able to take 100 years of stream flow data collected from a monitoring gauge between the McClure and Nichols reservoirs, and correlate it with tree ring growth.
Hook said Margolis’ work also helped them understand tree densities, how they are really high in the watershed and how to approach thinning the forests.
Haffey said one thing they wanted to look at was how often fires from outside the watershed burned into it. It turns out it was quite often.
Answering burning questions
From burn scars that leave resin cooked in the wood between rings, they are able to determine the size, frequency and intensity of wildfires over the years.
What the research, much of it conducted by Swetnam and Allen, shows in the Jemez Mountains is that, historically, fires were low-intensity blazes that burned close to the ground, removing debris and seedlings, but not killing many trees. As a result, the forest was less dense and the fires didn’t burn very hot.
That began to change dramatically beginning in the late 1800s, when cattle and sheep grazing helped to remove the fuel that would normally have been consumed by fire. Coupled with a forest management policy to suppress wildfires, the forest became denser and woodier. Over the course of 100 years, the Jemez Mountains became a time bomb that exploded with the likes of the Cebollita fire in 1971, the Cerro Grande fire in 2000 and the Las Conchas fire in 2011.
Forest fires in the Jemez Mountains had changed, crowning more often and burning much hotter.
“It’s one thing to have a fire on the stove; you can deal with that,” Haffey said. “What you don’t want is for the kitchen to be on fire.”
Haffey said that, based on the wet winter so far, the upcoming summer looks like a good time to conduct fire management operations.
“Wet years are good years to do fire management, because the risk for massive fire is low. These are years you want to see smoke in the air,” he said.