Study: Ponderosa pine ecosystems on brink of collapse
“We’ve developed a monoculture, instead of an ecosystem, and a forest that can’t sustain itself,” said Covington.
Fire, like the bark beetle, was once an important part of a healthy forest. Now it is a relentless predator. Whereas the bark beetle would break down dead wood and help put nutrients back into the soil, fire would keep dead and dying debris from building up on the forest floor. Its heat was also a necessary signal to some plants to sprout.
Today, both fire and the bark beetle have the power to destroy hundreds of thousands of acres. Covington says if large, landscape-scale restoration treatments are not implemented, every acre of Arizona’s ponderosa pine forest is likely to be affected by fire, insects or weeds, and degraded in about 20 years.
In the ERI lab, students work to sand and mount cross sections of fire-scarred trees that they’ve taken from centuries-old stumps in the forest. These cross sections contain a fire record in the tree rings. Each time a fire burns the tree, a dark indentation appears in the rings.
“Our research from these cross sections continues to reveal that fire occurred every two to seven years in the presettlement forest,” said Megan Van Horne, a forestry graduate research assistant with the ERI.
But then, around 1870, the fire scars disappeared. A look back at history offers an explanation.
In the late 1800s, millions of sheep and cattle were brought into the West. Researchers say they ate up the grasses that competed with other plants and kept tree populations in check. Without grass, fire had no path to burn across the forest floor, as it had in the past. In addition, fires were put out as fast as possible to protect ranches, livestock and communities.
Meantime, the ponderosa pine population enjoyed several big seed years. Without grasses and fire, the seedlings were able to become established. Those seedlings are now more than 80 years old, making up the thick, dark stands of skinny black-barked trees that act as ladders and bridges for fire and beetles to jump across and into the tops of the oldest trees on the landscape.
In the 1950s, a large wildfire was 5,000 acres. Firefighters then couldn’t imagine battling the monstrous infernos that have devastated huge tracts of the West in recent years.
“Knowing what we know, it’s unconscionable that we don’t take action now,” said Covington. “We’re out of time.”
Convington and the ERI promote forest treatments that mimic the forest structure of more than a century ago.
“You have to read the land to understand what it sustained naturally and where the trees grew,” he said. “Then you can identify the trees that likely would have been here, had humans not interfered. We’re talking about the big trees and the trees that ought to be released from the binding conditions that they are in. Once we’ve opened the forest, those stunted trees grow like teenagers. With this forest structure, fire can then be reintroduced and expected to burn at a low intensity that’s helpful to the forest.”
Currently, the ERI is studying the many parts of the ponderosa pine ecosystem and how they respond to thinning and prescribed burning.
“We don’t know everything and we’re never going to know everything, but we’ve got enough knowledge to know that we’ve got to get to work with restoration projects now,” Covington said. “With adaptive management, we can monitor and study the effects of restoration efforts and continue to improve our treatments. But, while we argue about what to do, the pines get weaker, the fires get bigger and beetle populations grow stronger.”
Covington’s work and restoration mantra continues to catch fire among mountain communities of the West, land managers and political leaders. Currently, Congress is considering a bill that would fund two more ecological restoration institutes—one in New Mexico and one in Colorado.