Although burned trees are the most visible damage following a wildfire, a forest’s soil can also be damaged. The heat generated by a wildfire can alter the soil’s physical properties and kill the fungi and bacteria that are responsible for nutrient cycling and other ecosystem services. What isn’t well understood is the extent of the heating within the soil and how quickly the soil recovers.
In the Pringle Falls Experimental Forest in the Deschutes National Forest, researchers with the U.S. Forest Service Pacific Northwest Research Station, Oregon State University, and Kansas State University conducted a study to compare the effects of low-intensity and high-intensity burns on soil organisms and nutrients. The high-intensity burns were simulated by burning “mega-logs,” a proxy for naturally occurring large downed wood. They established 12 sites and collected pre- and postburn soil samples and continuous temperature recordings during the fire.
As expected, the soil on the mega-log sites experienced intense heating. High temperatures penetrated 4 inches below the surface but no farther than 12 inches, and soil carbon and organic matterderived nutrients were volatized. There was also a substantial loss of nearly all the existing microbial communities. Within one week, however, fungi had returned; ascomycete fungi, such as morels, dominated the sites. Ponderosa pine seedlings were colonized by ectomycorrhizal fungi within four months.
PNW Research Station scientists are studying the dynamics of managing forests and landscapes after wildfires. Browse the publications below to learn more about the results of some of the Station's postfire forest management research.