Fire Induced Changes of Soil Structure: Implications for Soil Hydraulic Properties and Coupled Erosion by Water and Wind

Affiliation(s)PIProject periodFunded by
DHS Shafer, David S 09/15/2009 - 08/31/2010 National Science Foundation

Project Description

Fire-induced deterioration of soil structure has been identified as a key process that can significantly affect post-fire soil properties. Soil structure controls not only water and gas exchange at the air-soil interface but also erodibility of the soil surface by water and wind. Prior research has not connected fire effects on soil structure to post-fire erosion. Quantifying these impacts and their relationships would improve the prediction of post-fire infiltration, erosion through water and aeolian transport, and the potential for damaging floods and debris flows. Determining this relationship has been hampered by the challenge of quantifying fire effects before and after a burn at the same location. Most studies focus on post-fire effects without a true comparison to pre-fire conditions. In essence, experimental designs that seek to make these connections have not been implemented because of the unpredictable timing and location of wildfires, and the lack of recognition and quantification of fire-induced changes in soil structure. The Gleason Controlled Burn, to be conducted by the U.S. Bureau of Land Management (BLM) near Ely, Nevada, provides a unique opportunity to quantify the effects of fire on soil structure, and to test hypotheses on how fire-induced changes in soil structure can lead to coupled water and wind erosion. The timing for the burn and attributes of the site warrant an NSF RAPID Grant. First, the Gleason Controlled Burn is a planned event, and thus pre-burn and post-burn measurements can be conducted on pre-determined sites. Although the burn is planned for September or October 2009 (2-3 months in the future), the exact timing will depend on weather and fuel conditions. We intend to take pre-fire measurements in July and August, but only a few days notice will be provided before the burn actually takes place. Consequently, preburn measurements must be taken well in advance of the planned fire. Also, researchers must be ready to take post-fire measurements after the burn as soon as allowed. Second, the area to be burned has stronglydeveloped, coarse crumbled, surface-soil structure in unburned areas. However, where previous controlled burns have been done nearby, this soil structure has collapsed (Fig. 1) into a structureless soil, rich in fine particles, that will be prone to sediment yield and dust generation. We propose to revisit the plots periodically for one year after the fire to measure post-fire soil structure changes and to quantify the duration of elevated soil erosion conditions that we hypothesis will occur. The burn will be conducted in pinyon-juniper woodlands and sagebrush steppe, one of the most common vegetation assemblages of the intermountain western US that have been subject to increasingly frequent and large fires, particularly in the last decade. Between 1998 and 2008, an average of nearly 850,000 hectares (ha) burned per year in the western U.S., including over 1 million ha in the Great Basin in 2007 (Chambers et al., 2008).