February 20, 2003
Soil scientists from Colorado State University are investigating the 137,000-acre, 2002 Hayman fire site for microbial life and testing strategies to prevent erosion and help future fire sites quickly recover.
The Hayman fire ignited on June 8, 2002 southwest of the Denver metro area and was controlled by mid-July 2002. It was the largest wildfire in Colorado history.
According to CSU, Hayman fire temperatures reached in excess of 400 degrees Celsius (752 F). At least one area reached more than 650 C, more than 1,200 F. At 50 C, the small, single-cell organisms that live in the soil begin to die. At 300 C, organic matter including grass, trees and mulch are destroyed.
“The regeneration of soil life, such as fungi, is the first step to soil recovery after a fire,” said Mary Schutter, CSU soil microbiology assistant professor. “We hope that some fungal spores are heat resistant so that they can survive fires and regenerate themselves. Otherwise, we have to wait for them to grow back from the outside fringes of a fire.”
In some areas, where the fire did not reach the most extreme temperatures, soil life survived. Schutter will continue to test soil samples to measure the rate at which the fire site is regenerating and also will measure whether or not soil treatments such as hydromulch, a foamy man-made material that is commonly applied to areas burned by wildfire, speed up vegetation growth.
When organic matter burns in a hot forest fire, it forms a waxy layer on the ground, making the soil hydrophobic, and water beads up on the surface of soil instead of soaking into the ground.
“The waxy layer is fickle — if water sits on the surface long enough, it begins to soak into the first few millimeters,” said Greg Butters, CSU soil hydrologist associate professor. “But as soon as the water dries up, the waxy layer returns. Because the ground is not able to soak up water very efficiently, water begins to run on the surface and eventually erodes the soil.” The waxy layer increases the probability of severe erosion, floods and surface water pollution to nearby rivers, lakes and reservoirs, making it one of the more damaging aspects of a fire.
Soil can remain hydrophobic for two to three years. Hydromulch may speed up the destruction of the wax, which disintegrates naturally over time. But it’s not well understood why or how hydromulch works. Butters will focus on understanding why these treatments work and why microbrials in the soil respond well to them.
During heavy rains, the waxy layers of hydrophobic soil causes runoff, which may lead to flooding. The runoff also causes erosion as it picks up ash and other fine soil particles and carries them to streams and lakes, which can affect drinking water sources and water quality.
Adding environmentally friendly, water-soluble polyacrylamides to the topsoil helps soil bind into particles that are too large to be carried away by typical runoff. The polyacrylamides, called PAM, bind particles of silt and clay together, making them more resistant to erosion. They have been used to reduce soil erosion on farms.
“In irrigation tests, PAM increases sediment by up to 90 percent,” said Troy Bauder, Colorado State University Cooperative Extension water expert. “It’s fairly cheap and it breaks down in sunlight so it doesn’t stay in the environment long. I’m trying it on soil from the Hayman fire site to see if fire-damaged soils are fundamentally changed so that PAM won’t help binding. If it works, I’d like to find out why.”