Graduate Thesis Or Dissertation
 

Impacts of post-fire salvage logging on soil chemistry, physical properties and bacterial community composition in a mixed-conifer forest in central Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/vd66w233k

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  • Land managers, scientists, and the interested public are confronted with uncertainty about the impacts of salvage logging on soil productivity. In recent years, stand-replacing wildfires in the western United States have increased in frequency, prompting the need to evaluate the effect of post-fire treatments on forest ecosystem recovery. This study examined whether compaction and subsoiling after post-fire salvage logging impacted the structure, metabolism, and function of soil bacterial communities, which were assessed using terminal restriction fragment length polymorphism (T-RFLP) and Biolog Ecoplates. Supporting data for these salvage logging effects included soil biological activities, soil chemistry, and physical soil properties in a mixed conifer forest in central Oregon. Post-fire salvage logging treatments had little effect on soil bacterial community richness, suggesting that soil bacteria in these post-fire landscapes are both tolerant of the occurrence of fires and resilient to disturbance. However, even though a statistically significant difference in bacterial species richness was not detected among treatments, a greater cumulative mean number of species was found across six sampling seasons in the compacted soil treatment compared to the fire-only and subsoiled treatments. This trend may be due to less predation on the soil bacteria by microbivores in the soil pores reduced in size by compaction. Additionally, there was a significant decline in the mean number of species after the spring 2007 sampling. A NMS ordination of the mean number of species suggested that the bacterial community composition changed after spring 2007. Furthermore, the lack of difference in mean number of species among treatments suggests that time since fire had a stronger effect on the structure of the soil bacterial community than did logging disturbance. Plant-available phosphorus and nitrogen concentrations were lower in the mechanically disturbed treatments than in the fire-only treatment. Soil respiration and soil phosphatase rates both were higher in the fire-only treatment. Mechanical disturbance may have long-lasting effects in an already nutrient limited system. No other differences among treatments for soil chemical properties were detected. Soil bulk density was lowest in the subsoiled treatment. Microbial community responses to burning and compaction caused by harvesting can be negative, neutral, or positive. While many factors, in addition to soil chemical and physical properties, affect the microbial community richness and functional diversity, our results support other recent studies showing that soil bacteria are resilient in disturbed environments.
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