Charcoal Distribution Affects Carbon and Nitrogen Contents in Forest Soils of California

Fire is the dominant natural disturbance regime in most ecosystems of California. The long-term relict of fire is charcoal, which has been shown to increase N mineralization and also represents a pool of chemically stabilized C whose quantity and spatial distribution have not been well characterized in forest soils. We examined the charcoal content in three different ecosystems of the Sierra Nevada, including oak woodland (low elevation), mixed conifer (middle elevation), and red fir (high elevation). Using a fine-scale (2.5-m minimum resolution) spatially explicit sampling protocol applied to plots ranging between 0.25 to 0.5 ha, we examined the autocorrelation of forest floor and mineral soil properties including charcoal C. Charcoal C content ranged from 1000 to 5000 kg ha(-1) in the surface 6 cm of soil and increased with increasing elevation and latitude. Spatial patterns of forest floor and mineral soil properties were generally patchy at a scale of 5 to 20 in, except in the mixed conifer ecosystem (no pattern). The patchiness that existed at the other sites was largely a result of the distribution of total C and total N in the mineral soil. A spatial mixed-effect ANOVA indicated that charcoal had a 10 to 20% effect on C and N contents in both forest floor and mineral soil surface horizons, independent of other parameters including ecosystem type and total C or N. These results provide evidence that charcoal has a relationship with soil C and N content, which may influence soil biogeochemistry.