Thermal alteration of soil physico-chemical properties: a systematic study to infer response of Sierra Nevada climosequence soils to forest fires

Abstract

Abstract. Fire is a common ecosystem perturbation that affects many soil properties. As global fire regimes continue to change with climate change, we investigated thermal alteration of soils' physical and chemical properties after they are exposed to a range of temperatures that are expected during prescribed and wildland fires. For this study, we used topsoils collected from a climosequence transect along the western slope of the Sierra Nevada that spans from 210 to 2865 m a.s.l. All the soils we studied were formed on a granitic parent material and had significant differences in soil organic matter (SOM) concentration and mineralogy owing to the effects of climate on soil development. Topsoils (0-5 cm depth) from the Sierra Nevada climosequence were heated in a muffle furnace at six set temperatures that cover the range of major fire intensity classes (150, 250, 350, 450, 550 and 650 • C). We determined the effects of heating temperature on soil aggregate strength, aggregate size distribution, specific surface area (SSA), mineralogy, pH, cation exchange capacity (CEC), and carbon (C) and nitrogen (N) concentrations. With increasing temperature, we found significant reduction of total C, N and CEC. Aggregate strength also decreased with further implications for loss of C protected inside aggregates. Soil pH and SSA increased with temperature. Most of the statistically significant changes (p < 0.05) occurred between 350 and 450 • C. We observed relatively smaller changes at temperature ranges below 250 • C. This study identifies critical temperature thresholds for significant physico-chemical changes in soils that developed under different climate regimes. Our findings will be of interest to studies of inferences for how soils are likely to respond to different fire intensities under anticipated climate change scenarios.

Thermal alteration of soil organic matter properties: a systematic study to infer response of Sierra Nevada climosequence soils to forest fires

“…SOM is vulnerable to temperatures, while soil minerals are only affected at much higher temperatures (Araya et al, 2016). In addition, all of the soils in our study are characterized by low clay content and low concentration of reactive minerals, but they have a high concentration of SOM, especially in the topsoil, leading to strong relationships between SOM concentrations and soil physical properties.…”

“…We selected four forested sites that are likely to experience forest fires and a fifth lowerelevation grassland site. The thermal alterations in bulk soil physical and chemical properties from the same study soils were previously reported in Araya et al (2016).…”

“…Simple linear correlation between C concentration changes and other soil physical and chemical changes that we observed with heating (reported here and in Araya et al, 2016) show that more than 80 % of the variability in mass loss, aggregate strength, specific surface area (SSA), pH, cation exchange capacity (CEC), and N concentrations is associated with changes in C concentration at the different heating temperatures. Table 3 summarizes the correlation coefficients of soil property changes with change in C concentration.…”

“…The degree of alteration caused by fires depends on the fire intensity and duration, which in turn depend on factors such as the amount and type of fuels, properties of aboveground biomass, air temperature and humidity, wind, topography, and soil properties such as moisture content, texture, and SOM content (DeBano et al, 1998). The first-order effects of fire on soil are caused by the input of heat, causing extreme soil temperatures in topsoil (Badía and Martí, 2003b;Neary et al, 1999), which results in loss and transformation of SOM, changes in soil hydrophobicity, changes in soil aggregation, loss of soil mass, and addition of charred material and other combustion products (Albalasmeh et al, 2013;Araya et al, 2016;Mataix-Solera et al, 2011;Rein et al, 2008;Santos et al, 2016).…”

Post-wildfire Erosion in Mountainous Terrain Leads to Rapid and Major Redistribution of Soil Organic Carbon

“…The loss of vegetation that would otherwise stabilize soil in eroding landform positions, along with increased soil hydrophobicity after moderate severity fires leaves soil more directly exposed to weathering and erosion (DeBano, 2000;Shakesby et al, 2000;Larsen et al, 2009). Fires can also raise soil pH, alter cation exchange capacity, and change the soil organic matter (SOM) composition (Giovannini et al, 1988;DeBano, 1991;Certini, 2005;Liang et al, 2006;Araya et al, 2016).…”