Wildfire temperature effect on soils physical and hydraulic properties

Wildfires affect soil physical, chemical, and hydraulic properties, which in turn control many processes such as soil water availability, soil water balance, infiltration, and soil stability. Because of the multiple factors controlling the changes in soil properties and the nature of fire events, the number of predictive models for these effects is limited. Therefore, the objective of this study was to develop a soil-burning laboratory procedure to identify changes in physical and hydraulic soil properties across a fire temperature range. With this purpose, saturated hydraulic conductivity, pH, electric conductivity, soil texture, aggregate stability, repellency, and organic matter content (OM) were measured in soils burned at increasing temperatures. Six sandy loam soils were burned at four different temperatures (300ºC, 500ºC, 700ºC and 900ºC) and non-burned samples were used as a control to compute the change on each property. Additionally, three of these soils were sampled in a naturally burned area and used later to test the laboratory setup reliability to reproduce a natural fire. Preliminary results for soils burned in a muffle furnace (300ºC for two hours) showed that the changes in physical properties are more significant with soils rich in OM. On the other hand, properties such as water retention and hydraulic conductivity curves showed little variation at 300ºC.