SGER: Immediate Post-fire Response of Soil Biology and Pedogenic Processes at the San Dimas Lysimeter Biosequence.

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Research under relatively stable environmental conditions of the past 16 years has shown that biological activity strongly influences soil-forming processes at the San Dimas (California) research site. In September 2002, a catastrophic wildfire burned virtually all of the San Dimas Experimental Forest in southern California. This wildfire represents an extreme event that is nevertheless characteristic of chaparral ecosystems. Because the pre-fire conditions have been so thoroughly studied as at San Dimas, a rare opportunity is presented to advance the understanding of post-fire soil processes. This research will measure the initial post-fire response of biological communities and soil processes by addressing the following hypotheses: (1) Fine-scale variation in fuel loads created a fire severity mosaic in which recolonization by surface-active soil fauna and microbes will proceed from minimally burned patches; (2) Deeper-dwelling fauna were dormant in the dry soil and not immediately impacted, but as soils wet up in the coming months, these organisms (especially earthworms) will decline because of lost food sources, more severe microclimates, and altered soil chemical conditions; and (3) The initial water leaching into the soils will be highly alkaline because it passes through overlying white ash, and will lead to clay dispersion, destabilization of soil aggregates, a flush of waterborne clay, and increased silicate mineral weathering rates. These hypotheses will be tested by detailed field sampling, in situ monitoring, and laboratory analyses. These tests will identify mechanisms that control the trajectory of soil ecosystem recovery following fires. This research site will continue to serve diverse educational institutions through field trips and research opportunities.