While Californians have been coping with massive wildfires, filthy air, extreme heat and a deadly pandemic, fire damage incurred by old-growth trees in Big Basin Redwoods State Park has hit a particular nerve, especially with those who have once stood gazing skyward at these majestic icons of California's natural splendor.
But don't mourn too hard. Most of the ancient trees, some of them 2,000 years old, have survived, in Big Basin as well as in Armstrong Redwoods State Natural Reserve. And redwoods, well, they are tough. KQED recently spoke with Jeffrey Kane, associate professor of Fire Ecology and Fuels Management at Humboldt State University, about the species' resilience after a wildfire.
The following excerpts have been edited for length and clarity.
How does fire actually affect redwoods?
Jeffrey Kane: I'm struggling to think of a species as resistant and resilient as redwood. I always tell students, redwoods have belts and suspenders: They can deal with a lot of fire.
They have one of the thickest barks of any tree species. For conifers, they have this unique ability to resprout both from the base and from the entire bowl and crown of the tree. So it is really hard to kill a redwood with fire. It can be done, but it's pretty remarkable.
Fires provide a lot of benefits, too. They clean the understory. [The trees and plants that grow beneath a forest canopy.] They can help maintain the ecosystem composition. I went to look at the site of a fire in a redwood forest in Oregon; we saw lots of dead Douglas fir and also large redwoods resprouting. In the absence of fire, you get other species that come in, which start to become more common and compete with redwoods.
What would it take to kill a large redwood?
You’ve probably seen those big basal hollows, where fire gets inside the base of the tree and burns on up. I’ve actually been inside redwoods where you can see all the way up to a pinpoint of light at the top. And yet that tree is still alive. So they’re even pretty tolerant of that. Most of that wood in there is nonfunctioning, more structural. But if enough of that burns out, it can reduce the structural integrity of the tree, and then it may fall over because it doesn’t have enough strength to support its weight, or it may blow over in a windstorm. That happens in the absence of fire as well.
Historically, how many fires have burned through old growth redwoods?
We have lots of good data on this from tree-ring scars throughout the redwood range. It can be as frequent as every two years, but on average, most redwood forests have burned once every nine to 25 years.
Over the life of a tree, that can be hundreds of fires. Since redwoods occur in the coastal fog belt for the most part, the belief among researchers is that there must have been a large contribution of Native American burning to promote that frequent of a fire regime. But as we've seen, lightning can spark fires, and that's also part of the story. It could also have been that fires started in the drier interior before moving west into some redwood forests, especially during big wind events.
Might the forests be looking green and healthy again soon?
Yeah, definitely by next spring. I've seen them start to sprout just months after a fire.
Unless a large redwood topples, it's going to sprout even from the base. I mean, it's unlikely that a fire would be intense enough to kill all the growing tissues that are in the soil and the root ball. So you're going to have very rapid regeneration from asexual reproduction, which is the resprouts. And that's assuming that the aboveground tree dies, which again is kind of rare.
The other thing is if you go to a redwood forest and try to find a little seedling, you would be hard-pressed to find one, because they need bare mineral soil in order to germinate from seed [which are conditions created by fire]. So after a fire, you will get prolific regeneration from seed, where you probably wouldn't otherwise see it.
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