Collaborative Research: Alterations of Soil Physical and Geochemical Properties Induced by Low-intensity Fire

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The majority of fire research to date has focused on the negative impacts of large, medium-to-high intensity burns, which typically cause massive combustion of litter and organic matter in the topsoil followed by increases in soil erosion, runoff, and loss of nutrients. The positive role of fires in vegetation succession and nutrient cycling also is well recognized. In contrast, low-intensity burns (with soil temp. of 220 degrees C) are presumed to cause minimal soil degradation and landscape/ecosystem alteration. As a result, there has been only limited research investigating potential negative consequences of such burns, although they account for almost half of total burned areas in the United States. Furthermore, climate change is expected to increase the frequency and area of land exposed to such low-intensity burns. Recent long-term studies on the effect of low-intensity fires on soil structure, however, are revealing that substantial loss of soil aggregate stability and porosity occurs several months to a few years after the burn has occurred. These degradations in soil structure often are followed by reduced infiltrability and increased soil erosion. The overarching goal of this proposed research is to investigate the impacts of low-intensity fires on soil structure and the implication for soil hydrology, erosion, and nutrient dynamics. Specifically, this project is designed to test three hypotheses: a) soil structure deterioration is caused by micro-scale stresses created within aggregates due to rapid vaporization or thermal expansion of soil particles as well as preferential volatilization of mostly hydrophilic simple organic molecules; b) disaggregation and subsequent surface sealing result in reduced infiltration and increased erosion; and c) preferential mobility of nutrient-rich dislodged fine aggregates and particles results in accelerated loss of nutrients and carbon via lateral and vertical transport. The proposed research will be conducted using soil samples collected from arid and semi-arid ecosystems in eastern Nevada and will mimic characteristics of past low-intensity burns of the region.Improved understanding of how low-intensity fires can lead to land/ecosystem degradation will benefit society by enabling more effective design of controlled burns as well as post-burn land management practices. This knowledge also can play an important role in planning for mitigation of the effects of low-intensity fires in sensitive ecosystems and landscapes of arid/semi-arid regions that are expected to experience more fires as a result of climate change. This research will expand on-going collaboration with the Bureau of Land Management, thereby facilitating adoption of new advances to support science-based resource management. In addition, this project will provide educational and advanced research training to one Ph.D.-level student and one postdoctoral researcher. ?Science boxes? will be employed to engage K-12 students in results of the proposed project.