While the most obvious components of a forest ecosystem are above ground, perhaps the most essential elements are found below the surface. Forest soils are home to millions of microorganisms, such as molds, fungi, algae, cyanobacteria, rotifers, and protozoa, and larger soil invertebrates, including mites, snails, slugs, centipedes, spiders, nematodes, earthworms, and springtails. These perform physical and biological processes needed for a healthy ecosystem, including nutrient recycling, waste removal, soil structuring, and moisture retention. Wildfires add an extra variable to these ecological equations, and while some postfire effects are beneficial, others are so damaging that, without help, the system can take years to recover.
In a healthy forest, soil microorganisms
• Excrete organic glues that stabilize soil particles to enhance water retention
• Convert nutrients such as nitrogen and phosphorus from their organic to inorganic forms, making them available for plant absorption
• Increase the soil's porosity, which...
A wildfire can
• Increase surface soil pH by as much as 0.4–0.5, which alters the solubility of ions, especially those in nitrogen and phosphorus cycles
• Reduce the volume and diversity of microorganisms, sometimes to the point of sterilization
• Distill oils and aromatics from trees and shrubs, creating a hydrophobic ground layer, which increases erosion
• Quickly release nutrients into the ecosystem as inorganic ions for plant absorption, after low-intensity burns
• Volatilize or leach nutrients such as nitrogen and sulfur out of the ecosystem, after high-intensity burns
- Compiled by Maria W. Anderson
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