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

Abstract

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.

Fire history in northern Sierra Nevada mixed conifer forests across a distinct gradient in productivity

“…The highest proportion of scars in our study area were formed by fires that occurred between midsummer and late fall, when tree growth had ceased for the season, similar to the seasonal timing reported for other studies in northern California (Taylor and Skinner 2003, Taylor and Beaty 2005, Fry and Stephens 2006, Moody et al 2006, Gill and Taylor 2009, Vaillant and Stephens 2009, Stephens et al 2023. The predominance of fires recorded in the latewood and dormant period was consistent among sites, and between serpentine and non-serpentine soils.…”

“…The predominance of fires recorded in the latewood and dormant period was consistent among sites, and between serpentine and non-serpentine soils. This timing suggests that most fires in our study area likely occurred before the beginning of the wet season, as a result of ignitions from either lightning or cultural burning practices, at times when surface fuels were dry enough to promote fire spread (Moody et al 2006, Stephens et al 2023. The relatively high proportion of fires in the dormant season also includes the possibility that some indigenous ignited fires may have occurred in the winter months, when sunny conditions between storms could have dried out surface fuels (Stephens et al 2023).…”

“…The frequency of small fires, in combination with local variation in topography and abrupt changes in soil type, would have historically resulted in a spatially diverse mosaic of vegetation types, sizes, and age classes. This patchwork of burns would have limited the extent of subsequent fires by influencing the abundance and availability of fuel to burn (Collins et al 2009, Ireland et al 2012, Stephens et al 2023.…”

“…The landscape within our study area has been managed in both the distant and recent past. The Mountain Maidu have lived in this area for thousands of years and used fire to enhance young shoot growth for basket weaving, to clear hunting grounds, enhance California black oak stands, and reduce fire risk (Dixon 1905, Young 2003, Stephens et al 2023. More recently, forest thinning occurred in the area between 2003-2006, and small non-commercial trees and associated fuels were piled and burned (USDA Forest Service 2020).…”

Forest restoration and fuels reduction work: Different pathways for achieving success in the Sierra Nevada

“…More than a century of fire exclusion and early selective logging that focused on large trees has produced mixedconifer forests with high fire hazards (Hagmann et al, 2021;North et al, 2012;Safford & Stevens, 2017;Stephens et al, 2009;Stephens, Hall, et al, 2023). When this increase in live and dead vegetation is coupled with increased seasonal warming, it can produce prime conditions for large-scale forest loss (Cova et al, 2023;Parks & Abatzoglou, 2020;Parks et al, 2018;Steel et al, 2015Steel et al, , 2023.…”