Fire Effects on Soil

Fire affects the chemical, biological, and physical properties of soil (DeBano 1991). Specific effects of fire on soil may vary greatly depending on the fire intensity, ambient temperature, vegetation type, soil type, and soil moisture (Wells and others 1979).  These factors can produce either positive or negative effects on soil physical properties and soil nutrients.

The specific effects of fire on soil are largely determined by fire intensity. Evidence indicates that low-intensity prescribed fires have little adverse effect on soil properties. In fact, they may even improve soil nutrient availability. High-intensity prescribed fires have a temporary negative effect on site nutrient status resulting from volatilization of nitrogen and sulfur, plus some cation loss due to ash convection. Severe fires may potentially alter soil physical properties by consuming soil organic matter. They also have the potential to cause soil erosion and surface run-off. However, research conducted in the southern Appalachians suggests that these adverse effects of fire on forest soils have been minimal, even on steep slopes. Nonetheless, researchers present the following recommendations for maintaining soil fertility and structure after prescribed burns: 

1. Managers should strive to use burning prescriptions that minimize consumption of organic soil layers. Prescribed burns conducted when the lower forest floor and soil are moist seldom consume the entire duff layer, especially when relatively fast-moving head fires are used. Moisture not only protects the duff layer adjacent to the soil, but also prevents the fire from consuming soil humus and prevents heat damage to soil. Prescribed burns conducted when soil and fuel are too dry can consume soil organic matter and severely damage the soil (Buckner and Turrill 1999, Wade and Lundsford 1988, Clinton and others 1996).

2. Managers must take care when logging slash is burned on steep slopes. Surface runoff and soil erosion may occur before vegetation colonizes sites. The burning phase of the fell-and-burn technique should be completed by mid-September to allow herbaceous plants to seed in and provide a winter ground cover (Wade and Lundsford 1988).