Forest conditions created after catastrophic wildfires like last year's Carr and Camp fires in Northern California can be conducive to another major fire in the same area just a few years later, University of California scientists say.
Along with leaving dead trees and branches and other burned debris in their wake, hot fires seed a more fire-adapted underbrush that can come back ferociously, explains Ryan Tompkins, a University of California Cooperative Extension forestry advisor.
"In the last 10 years, we've seen systems change before our eyes," Tompkins told about 100 researchers, government officials and growers at a June 4 symposium on the Camp Fire's environmental fallout. The event was held at the California State University-Chico farm.
"Restoration isn't just a one-off event," he says. "We need to play a long game."
For private landowners, the long game could include planting timber stands in cluster configurations rather than a simple grid and paying closer attention to vegetation, Tompkins and other scientists say.
"Plan for landscapes to burn again," he says.
Forests 'adapted with fire'
Throughout history, forests "adapted with fire -- frequent, low-intensity fire," Tompkins told the Chico gathering. However, after a century of fire suppression and land management, researchers notice that landscapes are re-burning sooner than imagined, he says.
For one thing, there's often a very vigorous native shrub response to the initial fire. Existing shrubs can sprout from their roots after being top-killed, and many new shrubs can germinate because the seeds in the soil are often stimulated by wildfire, UC researchers Kristen Shive and Susan Kocher write in a 2017 essay on wildfire recovery.
These dense shrubs could crowd out naturally occurring seedlings and later combine with dead, fallen trees to create high fuel loads, the scientists explain. When another fire comes through, it may burn hot enough to virtually wipe out all underlying vegetation, providing little habitat for wildlife while leaving little defense against excess water runoff.
"Managing that shrub component is another important aspect of your recovery interactions," Tompkins says.
Even after a moderately severe fire, a landowner may need to consider removing individual dead or damaged trees for safety or economic reasons, Shive and Kocher advise. Even in more moderate fires, property owners could lose timber revenue or have to contend with standing snag hazards and future fuel loading.
"Just because an area burned in low severity doesn't mean it's in a desired condition" or will be resilient in the next fire, Tompkins says.
Assess more broadly
While a landowner is likely to focus restoration efforts in areas with the highest tree mortality, it's important to assess safety more broadly, such as considering whether increased flooding could lead to plugged culverts or damage to roads or homes downhill, Shive and Kocher write.
Replanting after a major fire provides an opportunity to diversify reforestation tactics by manipulating planting density and arrangements, Tompkins says. He suggests that planting seedlings of multiple species in clusters at wide and variable spacing would produce higher spatial heterogeneity than the standard grid pattern. Such an approach would require less long-term maintenance such as pre-commercial thinning as stands develop, he posits.
To read the full report by Shive and Kocher, tilted "Recovering from Wildfire: A Guide for California's forest landowners, visit https://bit.ly/2HGHOcb. For resources related to the Chico symposium, visit https://ucanr.edu/sites/Rangelands.