Effect of Combustion Temperature on Soil and Soil Organic Matter Properties: A Study of Soils from the Western Elevation Transect in Central Sierra Nevada, California

Abstract:

Fire is a common ecosystem perturbation that affects many soil physical and chemical properties and soil organic matter (SOM). We investigated the effect of combustion temperatures on the physical and chemical properties of five soils from an elevation transect that spans from 210 to 2865 m.a.s.l. along the Western slope of the Sierra Nevada. All soils formed on a granitic parent material under either oak woodland, oak/mixed-conifer forest, mixed-conifer forest or subalpine mixed-conifer forest ecosystem. Soils show significant differences in SOM content and mineralogy owing to the effects of climate on soil development. Soils from 0 to 5 cm depth were combusted in a muffle furnace at six different temperatures within major fire intensity classes (150, 250, 350, 450, 550 and 650ºC). We determined the effects of combustion temperature on aggregation; specific surface area; pH; mineralogy; cation exchange capacity; carbon (C) and nitrogen (N) content; ¹³C and ¹⁵N isotopic composition, and distribution within aggregate sizes; and quality of SOM through infrared spectroscopy. Among other things, we found significant reduction total C and N, accumulation of aromatic carbon functional groups, and loss of aggregation with implication to loss of protection of C as the combustion temperature increases. The findings demonstrate that most significant changes in the soils physical and chemical properties occur around 350ºC. Findings from this study are critical for estimating the amount and rate of change in C and N loss, and other essential soil properties that can be expected from topsoils exposed to different intensity fires.