Tree rings tell CSUF students about droughts and fires in the Sierra

Some students plant trees. Some hug them. This summer, eight Cal State Fullerton students sampled trees.

Really, the students were listening to what trees had to say about the droughts and fires they had lived through.

Specifically, the students extracted cores from trees in the Sierra Nevada – including some in Yosemite that had burned a few years ago – and are now examining the cores back on campus.

A new laboratory, the Cal-Dendro Tree Ring Laboratory, has been set up to conduct research on the cores, which are expected to reveal valuable data going back 500 to 1,000 years.

Such data will give researchers a better idea of what the area’s normal hydroclimate is and help inform policies involving water management, said Trevis Matheus, assistant professor of geography and the environment, who specializes in dendroclimatology.

“This also helps put climate change into context, as it is hard to know where you are going if you do not know where you’ve been,” said Matheus, who joined the CSUF faculty a year ago.

Matheus had been interested in the physical sciences since he was a kid. He would stare up at the clouds in awe and wonder what processes were involved. In high school, he competed in national and international science fairs with projects involving climate research.

Matheus took eight students in his Mountain Field Geography class to Sequoia and Yosemite national parks for 10 days over the summer to learn how to sample trees.

The sites they visited had been sampled in the 1970s and 1980s in relation to precipitation totals. With new techniques, CSUF researchers are hoping to reconstruct snowpack totals in the Sierra Nevada over the past 500 to 1,000 years.

“What we can do is look at light bands in tree rings and correlate that to snowpack,” said Matheus. “Looking at snow, rather than runoff, is an important distinction because it is the source of our water supply.

“When we have droughts, they might seem severe on a local time scale, but the trees are going to report how droughts fit into a long-term context and give us some idea of what we can expect for the future.”

In Yosemite, the team sampled trees that burned a few years ago, extracting data that could lead to insights in the field of dendropyrology, which examines fire scars in trees.

“Every time a tree burns, it will have a scar,” Matheus said. “Looking at the scars under a microscope, you can determine when a fire occurred in a tree. If you can sample enough trees over a large area, you can also determine how widespread the fires were and how common they are.”

For every hour the researchers are in the field, Matheus estimates they return home with roughly five to eight hours of lab work. The new CSUF lab houses field sampling gear, two microscopes, sanding equipment and a computer to analyze the data. Matheus anticipates that two to three research papers will result from this summer’s trip.

By examining how far apart or close together the rings are, researchers can determine how well the surviving trees are growing after a fire, he added.

Graduate student Raymond Villalba is using the lab to work on his thesis project on the growth response of sugar pines in the Sierra.

Villalba described the summer field work as “mentally and physically challenging” – waking up at 5:30 a.m. and hiking several hours through steep terrain to reach sites up to 10,000 feet altitude – and “a great experience” he will never forget.

The process of sampling included drilling into a tree and extracting two pencil-size cores – which doesn’t harm the trees – recording the latitude and longitude of the tree, measuring the diameter of the tree, and using an inclinometer to estimate its height. Matheus and his students sampled 80 trees.

“I’m growing this love for dendrochronology, and I want to keep doing this,” Villalba said.

With climate change a global concern, Villalba’s goal is to teach geography at the community college level to help educate future policymakers.

“Maybe someone who is planning to be a lawyer, a politician or an engineer will learn more about the environment in one of my classes,” he said. “Maybe that’s the contribution I can make to this world.”

To view a one-minute video of the students sampling trees, go to youtu.be/MIVfHTdvdYs.

Cal State Fullerton News Service contributed to this report.