Impact of fire on soil life and nutrients
The impact of fires on vegetation and wildlife is obvious. Less obvious is the impact of fires on soils. What happens to the soil life, and to soil nutrients?
Italian research found that soil biodiversity recovers quickly after fire but soil fungi take longer to recover than bacteria. Nutrient levels and soil organic matter both increase after fire.
Spanish research showed a significant increase in soil pH, carbon and nutrients immediately after a prescribed grass fire.
A year later, pH and total carbon had returned to pre-fire levels, nitrogen and phosphorus werea bove pre-fire levels, but potassium was lower.
Spanish laboratory studies found that heating soils up to 400 degrees C enriches available nutrients and stimulates bacteria even without ash.
However, temperatures above 400 degrees have a detrimental effect on microorganisms until vegetation recovers.
One of the greatest issues for soil recovery after fire is heavy rainfall.
The combination of fire and torrential rain can prevent revegetation, leading to land degradation which may be permanent.
While vegetation regrowth usually reduces surface waterflow and soil erosion, US research has found that pine regrowth on fire-affected soils is associated with water-repellent soils, so forest establishment may not be the best way to rehabilitate some burnt sites.
Research into the impact of fire on soils is difficult.
Scientists need to study sites that have pre-fire data already collected so they can compare the post-fire soils, but it is hard to anticipate where fires might strike.
Findings in one region or country may not be applicable to other areas due to differences in climate, vegetation cover and land management.
However, the limited research that is available shows that fires can have profound effects on the soil ecosystem, leading to short and long term changes.
If you’d like to read more about the latest research, the International Journal of Wildland Fire has just published a special issue on fire effects on the soil system.
You can find out more at http://www.publish.csiro.au/nid/114.htm.
This column appears in Agriculture Today.