Degradation and restoration of Indigenous California black oak ( Quercus kelloggii ) stands in the northern Sierra Nevada

Background The cultural connections of the Maidu to the lands they inhabit are profound with burning being a major component of their culture. California black oak plays an important role in the lifeways of many Indigenous tribes and Native peoples tend black oaks. We used multiple lines of evidence to reconstruct Indigenous fire use in a mixed conifer forest in the northern Sierra Nevada. This includes summarizing oral traditions by the Mountain Maidu, quantifying current and historical forest structure, and characterizing fire effects in an area impacted by the 2021 Dixie Fire. Results The promotion of fire, both lighting- and human-ignited, has always been part of Mountain Maidu land stewardship. The mixed conifer forests in our focal study site had very high tree densities that were dominated by small, shade-tolerant species and the historic mean fire return interval was 8.6 years. Twenty-three fire intervals of 10 years or less and 11 fire intervals of 5 years or less were recorded. Based on forest inventory data collected in 1924, a majority of the forests in the broader region surrounding our focal site (82%) did not experience high levels of conifer competition. This is a stark contrast to contemporary forest conditions which showed that 73% of forests either were experiencing full site occupancy or were within the zone of imminent mortality. Contemporary forests not experiencing high levels of conifer competition had the highest density of large California black oak while forests in the zone of imminent mortality had the lowest density of large California black oak. Conclusions Fire exclusion and suppression led to a slow, albeit catastrophic, shift for California black oaks. The mixed conifer forests sampled in the early 1920s had very low tree densities and were dominated by large ponderosa and sugar pine trees which would have allowed California black oak to thrive. The number of very short fire intervals recorded is difficult to explain by lightning alone, pointing to the management of this area for Indigenous purposes. The 2021 wildfire resulted in 100% mortality of all conifer trees in the area but 61% of the California black oaks resprouted. This provides an opportunity to remove the conifer snags and allow the California black oaks to regain dominance. It would take active stewardship to produce the oak dominance again but it is possible and could be co-led by the Maidu and federal managers.