Effects of fire‐induced water repellency on soil aggregate stability, splash erosion, and saturated hydraulic conductivity for different size fractions

Abstract

AbstractForest fires can alter several soil properties influencing soil erosion and runoff processes in addition to removing all or part of the vegetative cover. These include organic matter content, aggregate stability and water repellency. Soil erodibility and saturated hydraulic conductivity depend on these properties and their response varies according to aggregate size. The objective of the study was to investigate how forest fires affect key soil properties and determine the potential impact of these on runoff and erosion processes. The A horizon of an acidic sandy loam was collected and subjected to a pine litter fire. The burned and control soil samples were separated into 4 size fractions: bulk (<5·0 mm), < 0·4, 0·4–2·0, and 2·0–5·0 mm. Organic matter (OM), aggregate stability mean weight diameter (MWD), and water drop penetration time (WDPT) were measured for each size class. Each size fraction sample was subjected to 0·5 h of simulated rainfall (55 mm h−1) for splash erosion measurements. Saturated hydraulic conductivity (K) measurements were performed on the same samples. Burning the litter decreased soil OM content but increased MWD and WDPT. Splash erosion increased greatly for the bulk and < 0·4 mm samples. MWD increased for the 0·4–2·0 and 2·0–5·0 mm size fractions despite a loss in OM and clay content in the burned soil. A surface crust never formed on the water repellent fine fraction leaving plenty of non‐cohesive material available for soil detachment. Increased water repellency reduced K for all size fractions. The data support the need for a specific soil erodibility index for post‐forest fire soils. Copyright © 2007 John Wiley & Sons, Ltd.