California’s Sierra Nevada region has been home to mixed conifer forests for centuries, but shifting conditions have left these giants stuck in areas known as zombie forests - places where mature trees exist but producing younger trees has become a struggle. The Moore Foundation partnered with researchers Chris Field, Avery Hill, and Connor Nolan at the Stanford Woods Institute for the Environment to support efforts to identify, map, and explore adaptive management solutions for these zombie forests, a potentially critical risk factor for catastrophic wildfire and long-term vegetation change in California.
To map these zombie forests, the team examined historical data going back as far as the 1930s to track vegetation and used a climate-niche-modeling technique based on the idea of vegetation disequilibrium. They found that the conifer forests have shifted an average of 112 feet higher, while their ideal temperature range has moved around 600 feet higher, resulting in at least 11% of current conifer forests in mismatched conditions.
“In mid-July, we brought together about 20 local community scientists in Grass Valley, California to collect biodiversity data in a Sierra Nevada zombie forest using iNaturalist. Together we found noticeable differences between areas where our models predicted vegetation-climate mismatch and adjacent, more stable, conifer forests,” said Avery Hill, Ph.D. and postdoctoral researcher at the California Academy of Sciences. “This event was a very encouraging step towards ground-truthing our model predictions and identifying a number of zombie forest indicator species in the Sierra Nevada, and we plan to expand the community science campaign in the coming years.”
Historically, lower and mixed-severity fires at regular intervals served an important ecological role cycling nutrients and succession in conifer forest. However, a century of fire suppression practices has led to more vegetation growth, which can act as fuel for more destructive fires, and leave the landscape inhospitable for ecosystem recovery.
While some forests may gradually shift to higher elevations for their own survival, this movement also means competition with other species. Researchers are studying different management approaches and implications, including enabling beneficial fire.
Given the increasing frequency of severe wildfires, a shift in landscape management is necessary to mitigate their consequences. Research has shown that low-intensity fires mitigate the risk of high-intensity wildfires in California’s forests. Prescribed and managed fires can be instrumental in mitigating the risk of severe wildfires overall. However, investments in these types of interventions should be recurrent and understood as ongoing stewardship, informed by predictive ecology rather than one-time efforts based only on the conditions today.
Additional Resources
Images: Areas of a burned "zombie forest." Courtesy of Avery Hill.
Message sent
Thank you for sharing.