Burned in wood: Study uses tree rings to trace Taos-area fire history

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Ellis Margolis tears a shield-sized slab of bark from a rotten ponderosa pine stump up Taos Canyon and shakes it above his head.

“That’s evolution, man,” Margolis exclaims, gripping the hunk of sturdy tree armor with both hands.

His point: This and other ponderosas didn’t just tolerate wave after wave of wildfire over their centurieslong lives. They depended on them.

Lively and lanky as a young pine, Margolis is an expert in tree ring analysis. He specializes in piecing together the history of fire on landscapes in the Southwest. This summer, Margolis and other researchers are combing the forests above Taos looking for evidence of wildfires going back hundreds of years.

Margolis says if we know more about the way wildfires naturally burned — back before humans started stamping them out indiscriminately — we might be able to take steps to make our forests more resilient.

“If you take fire out of a system, it’s like taking water out of a river,” Margolis says, scanning the hillside that probably hasn’t seen a real blaze for 130 years.

Low-intensity fire helped clear out underbrush and smaller trees that compete for water and nutrients. Fire also helped enrich the soil and kept potential fuels from accumulating to dangerous levels. “So much of what was going on here depended on the kind of returning fire that we haven’t seen for a long, long time,” Margolis says.

That’s why a complete fire history can serve as a kind of map to get forest health back on track. “It tells us this is the way it was, this is the way the forests were the healthiest and this is the way it should be,” he says.

Forest evolution

Margolis explains that all trees and forest types in our region evolved with fire. However, he and other land managers say most of the Carson National Forest is out of whack. Very successful fire suppression efforts over the last century kept blazes from threatening human lives and infrastructure, but they also prevented fires from fulfilling their ecological duty.

In many places, the result is a thicket of smaller, weaker trees that are actually primed to blow up into far more powerful infernos.

Margolis points to the Jemez Mountains near Santa Fe, where massive wildfires like the Las Conchas Fire tore through the forest with an intensity that was way outside the norm. The aftermath included a barren landscape and landslides that dumped rivers of ash into the Río Grande.

“A third of that forest has turned into shrubland and it’s changing the landscape,” says Margolis, who’s done extensive research on that side of the basin. “And it’s probably going to stay like that. [The forest] is not going to come back.”

Fire and water

In response to those sorts of catastrophic blazes, a public/private coalition known as the Río Grande Water Fund has formed to pool resources and treat hundreds of thousands of acres of forests in New Mexico that serve as a water source for much of the state.

Margolis is part of a research team hired by the Río Grande Water Fund to develop a long-term fire history for parts of the Río Grande Basin, including areas of Taos County. That history is meant to serve as irrefutable evidence that moderate fire had always been intrinsic to the forest – and should be again.

The U.S. Geological Survey and The Nature Conservancy are collaborating on the current study. The study is funded with a $125,000 grant from the Taos Ski Valley Foundation, with another $115,000 from federal and local governments.

This summer, field crews have been scouring the forest looking for evidence of past fires. Around Taos, they’re doing studies for the Río Fernando, Río Pueblo and Río Hondo watersheds.

By cobbling together hundreds of samples, researchers say they’re able to paint a vivid and surprisingly specific picture.

At one location up Taos Canyon — a west-facing slope near the summit of Palo Flechado — the team collected 10 samples from ponderosas that were probably harvested for lumber in the ‘70s. Crews cut cross-sections from the leftover stumps, which had tell-tale markings of fire damage.

“There are distinctive cathedral-shaped wounds that go to the ground,” says Lane Johnson, a data analyst with the National Park Service who has been in the field turning over logs and inspecting stumps for weeks.

Fire on some trees can leave a wound, which is prone to reopen during successive fires. The tree survives, but with scars. And the scars tell the story.

Samples from this hillside will be taken to the lab, where they are buffed up with sandpaper to make it easy to distinguish the growth rings. On a complete sample, growth patterns usually tell researchers exactly when the tree sprouted, when it was exposed to fire and when it finally died.

Samples from Taos County haven’t yet been analyzed in the lab, but Johnson says these stumps show at least seven fires that probably date back to the 1600s. The most recent fire was probably around the 1880s, Margolis says.

On average, that’s fire every 30 years or so. It was fire that was strong enough to burn the tree and most likely take out some of its competition, but not strong enough to kill it.

But there’s no evidence of fire at all in the last 130 years. Instead, Margolis expects tree rings to show stunted growth because of competition from tiny trees that now fill open areas across the slope.

For Gabriel Romero, a silviculturist with the Carson National Forest, that’s useful knowledge. “This kind of information reinforces what we’re thinking and helps us in the decision-making process,” Romero says.

The ultimate goal of the Río Grande Water Fund is to find the money and the political will to restore forests to a more natural condition. If the Forest Service decides to thin a part of the forest with chainsaws or use prescribed fire to reduce fuels, it’s up to Romero to decide which trees should stay and which should go. If he knows the frequency of fire in a specific draining or even up a specific canyon, he says he’s better able to create a plan that mimics the natural ecology.

“The data will tell us what’s been lacking in this system and what we need to do to bring it back,” Romero says.

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