The 2003 Booth and Bear Butte Fires in central Oregon burned nearly 37,000 hectares, creating a mosaic of forest disturbance in the Deschutes and Willamette National Forests. The impact of fire and post-fire management activities on the belowground ecosystem is of special concern to future forest recovery. Salvage logging, primarily for economic gain, sometimes follows severe fire. Disturbances such as fire and salvage logging can impact the abundance, activity, and composition of soil microbial communities, thereby contributing to changes in nutrient cycling, rates of organic matter decomposition, and system carbon accrual. Salvage logging frequently results in soil compaction, reducing soil pore size and decreasing oxygen availability and movement of water and nutrients to tree roots. To alleviate compaction, the practice of subsoiling is used to fracture the lower soil strata, but this disruption of the belowground component may have immediate and long-lasting effects to the whole ecosystem. The objectives of this study were to determine the effects of compaction and sub-soiling after post-fire salvage logging on soil microbial communities (relative abundance of bacteria) and their metabolism (as measured by respiration) in a mixed conifer forest located in central Oregon. The study is a complete randomized block design with six post-fire salvage logged stands (blocks). Within each replicate stand, three treatments were established (burning with no further disturbance, compaction from heavy ground-based equipment, and compaction followed by subsoiling). Three plots per treatment unit were randomly sampled for a suite of soil chemical, physical, and biological response variables.
Results/Conclusions
Few differences among treatments were detected in soil chemistry and physical properties. The bacterial community consisted of a few abundant species and a large number of infrequently detected species. A total of 65 and 73 terminal restriction fragments (T-RF species) for restriction enzymes Alu and Msp respectively, were detected in 5 or more samples. Although there were differences among stands with respect to relative species abundance, there was no difference among treatments. Soil moisture, respiration, temperature, LOI, and bulk density were significantly correlated to the variation in soil samples. Because soil microbes are responsible for decomposition and nutrient cycling, changes in their composition and function will likely affect site productivity. However, preliminary analyses of results suggest that salvage logging treatments had little effect on soil bacterial communities in sandy loam soils in central Oregon.
