Soil Degradation During Low‐Severity Burns

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A paper from Mathew Jian’s MS thesis, describing Soil Structural Degradation During Low‐Severity Burns was accepted in Geophysical Research Letters.

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The Carpenter 1 fire (July 1, 2013 to August 18, 2013 [containment]) burned approximately 11,000 ha in the Spring Mountain National Recreation Area (Humboldt-Toiyabe National Forest) near Las Vegas, Nevada. The fire affected subalpine pine ecosystems at 3400 m to arid desert scrub ecosystems at 1500 m. The photo shows the lower-elevation boundary of the burned area, where low-severity fired burned off scarce vegetation. Photo courtesy of Teamrat A. Ghezzehei.

Plain Language Summary

Fire researchers and the public are often concerned about the increasing threat of fires that are considered moderate to high in intensity—a measure fuel energy—and in severity—a measure of impact on ecosystems. What does not get much attention is, however, that the area impacted by low‐severity and low‐intensity fires is also on the rise. Currently, more than half of the burned areas in the southwestern United States are low‐severity wildfires and controlled burns. These fires last only for a few minutes, and the soil surface temperature rarely exceeds 200 °C and does not heat more than a few centimeters of soil. Because of this low energy input, the effect of low‐severity burns on soil quality has been generally assumed negligible. This study was motivated by long‐term monitoring studies in Spain and United States that showed significant disaggregation of surface soil occurred several months after low‐severity burns. Here we show that soil water is vaporized very rapidly when moist soil aggregates are subjected to rapid heating. The escaping vapor momentarily creates disruptive stress that may exceed the bonds that hold soil aggregates together, causing disaggregation and loss of soil functions such infiltrability, resistance to erosion, and protection of organic matter.