Last spring, a tree-planting crew hiked into the hills near Paradise, California, to take on a challenge: What’s the best way to replant a forest when it’s very likely that it could burn again?
So far in 2020, more than 4 million acres have burned in California—an area roughly the size of Connecticut. It’s a record-breaking amount. It’s also a continuation of a long-term trend: Combine climate change that makes the state hotter and drier with decades of fire suppression, and megafires are becoming more common. The Camp Fire, which burned through Paradise in 2018, killing 85 people and leveling thousands of homes, was one of a series of fires in the area. This year, as fires raged nearby, people living there were forced to evacuate again.
As wildfires get bigger, they destroy everything in their path, which makes it harder for forests to grow back once they pass. Without intervention, some burned forests could turn into shrubby grasslands. “The fires are coming back so frequently, and they burn so hot, that they take out all the mature, seed-bearing trees,” says Austin Rempel, senior manager of forest restoration at the nonprofit American Forests. “There just isn’t a source of seed for trees to come back after fire. What fills the gaps is the grasses and shrubs. We’re basically talking about semipermanent forest loss.”
That’s a problem not only for the ecosystem, but also for climate goals: Trees are very effective at sucking up carbon dioxide (CO2) and storing it as they grow. In California, preserving forests is part of the state’s cap-and-trade system. Globally, forests are necessary to reach net-zero emissions. But replanting after a fire isn’t as obvious a benefit if the new trees just risk going up in smoke.
A different approach to planting, though, can reduce that risk. In some cases, that involves fixing past mistakes. Traditionally, planted forests looked like rows of crops, in what Rempel says was called the “pines and lines” model. The trees were planted close together to shade the ground so shrubs wouldn’t grow, with the idea that someone would come back a decade later to thin out the trees. But the Forest Service and other forest managers often haven’t had the resources to do that, leaving trees closely bunched together. “The trees can burn really easily because the fire just passes from treetop to treetop, so they can take out your entire planting project in one fell swoop,” Rempel says.
In April, Rempel traveled to California to assist the Bureau of Land Management with replanting an area like this—a pine plantation—that had been obliterated by the Camp Fire. “I found the earliest satellite photos of this bit of the property where we were working, and it looked really healthy in the ’50s,” he says. “It was a pretty natural-looking matrix of shrubs on the ground, and then empty spaces, and then some conifers and some oak. It was a diverse, really heterogeneous forest, and that’s what you need to be able to survive fire. So it looks great in the ’50s. And then they convert it to a pine plantation, which was the trend for a lot of forests. That homogenized it, and that really makes it susceptible to fire.”
Because the coronavirus crisis put most Bureau of Land Management staff on lockdown, American Forests ended up handling most of the planting. One key strategy was something Rempel compares to social distancing—planting trees in small clumps that are irregularly spaced and far enough apart that a wildfire can’t jump between clumps. The technique isn’t yet fully proven, but it’s becoming more common, and anecdotal evidence suggests that it helps more trees survive if a fire comes through an area.
It also helps to replant trees that have the best chance of survival. Sugar pines, for example, have been hit by disease. But it’s possible to visit an area where the trees have been killed, find a tree that managed to survive because it had the right genetic resistance, and then collect seeds from it and raise seedlings that can then be planted in an area that has burned. “We can maybe speed up natural selection by planting,” Rempel says.
The types of trees in the area also need to change. “It’s very common to look at what was there before the fire and just say, let’s replace that one for one—try and get the exact same seed, exact same trees, and replant them,” he says. “But that doesn’t make sense when looking out 30, especially 60 years from now.”
In the Camp Fire burn scar, that means planting more oaks, for example, trees that are more common at lower elevations now, and that are better adapted for both heat and fire. Other groups working in the area, including the Butte County Resource Conservation District, are taking the same approach as they work on replanting. The area, like other forests in the state, will have to be managed differently as well, with prescribed burns to help reduce the risk of more catastrophic fires.
Around 30% of the forests that burned in California and Oregon this year were probably damaged so significantly that they’ll need replanting because they can’t regenerate on their own. That’s more than 1.5 million acres of land to cover. But there are many obstacles: There’s only a two-year window to work, Rempel says, before grass and shrubs take over. There’s also a shortage of seedlings at nurseries. And the permitting process to plant on federal land is slow. Organizations working on the problem will have to get creative, including, potentially, using drones to plant trees. “If we had drones that could just be immediately deployed to the fire scars, we would be able to make that two-year window,” Rempel says.
Another challenge: There’s a risk that another fire could come as the young seedlings are just starting to grow. It nearly happened this year, as two major fires unexpectedly approached again. “There’s a PG&E [Pacific Gas and Electric] monitoring camera right above our planting site and I was glued to it for about a week, always expecting to see flames come over the ridge,” he says. “But it never happened—we got lucky. I’m still shocked that the Bear Fire and North Complex reburned so many parts of the Camp Fire burn scar. Normally you’d expect to have a longer grace period after a big fire like the Camp Fire. Firefighters said they’d never seen fire behavior like they did the night the Bear Fire got away.”