Fire Ecology - Abiotic Responses

Abiotic Responses

Fire has important effects on the abiotic (non-living) components of an ecosystem, particularly the soil. Fire can affect the soil by direct contact with it and by its effects on the plant community associated with it. By removing overhead vegetation, fire can lead to increased solar radiation on the soil surface by day, resulting in greater warming, and to greater cooling through the loss of radiative heat at night. Fewer leaves left to intercept rain will allow more moisture to reach the soil surface. In addition, plant transpiration (the process by which water travels through plants and evaporates through pores in the leaves) will be reduced following a fire, allowing the soil to retain more moisture. Exposure to sunlight, wind and evaporation, however, will work in the other way, to dry the soil. The fire may have created an impermeable crust at the soil surface, if organic matter on the ground was heated by the fire into a waxy residue, and if this has happened, it may lead to increased soil erosion through surface run-off.

Fire may cause nutrient loss through a variety of mechanisms, including oxidation, volatilization, and increased erosion and leaching by water. Temperatures must be very high, however, to cause a significant loss of nutrients, which are often replaced by organic matter left behind in the fire. Charcoal is able to counteract some nutrient and water loss because of its absorptive properties.

Overall, soils become more basic (higher pH) following fires because of acid combustion. By driving novel chemical reactions at high temperatures, fire can even alter the texture and structure of soils by affecting the clay content and the soil's porosity.