Fire effects on soil nitrogen dynamics in coniferous forests of central Idaho, USA


Koyama, Akihiro.. (2007). Fire effects on soil nitrogen dynamics in coniferous forests of central Idaho, USA. Theses and Dissertations Collection, University of Idaho Library Digital Collections.

Fire effects on soil nitrogen dynamics in coniferous forests of central Idaho, USA
Koyama, Akihiro.
Soils--Nitrogen content--Effect of fires on--Idaho Taigas--Effect of fires on--Idaho
Natural Resources
Forest fires are one of the most important natural disturbances in the inland Northwest, USA. Forest fires influence biogeochemical cycles of nitrogen (N) in forest ecosystems. It is critical to understand how forest fires alter N dynamics in soils because N is often a limiting nutrient in coniferous forests of the inland Northwest.;Effects of wildfires on gross fluxes of inorganic N (i.e. NH{esc}b4{esc}s and NO{esc}b3{esc}p-{esc}s) in mineral soils were investigated using {esc}p15{esc}sN isotope pool dilution in intact cores two years after three wildfires that occurred in summer 2003. Gross nitrification rates were not altered by the wildfires. However, microbial uptake rates of NO{esc}b3{esc}p-{esc}s and NH{esc}b4{esc}s, and ammonification rates were significantly reduced in burned soils relative to controls. These reduced N fluxes were caused by reduced carbon (C) availability in burned soils.;Effects of wildfires and prescribed fires on gross inorganic N fluxes in riparian soils were compared using {esc}p15{esc}sN isotope pool dilution in mixed soils incubated in the lab. Three watersheds burned by wildfires that occurred in summer 2003 and three watersheds burned by prescribed fires conduced in spring 2004 were chosen. All the watersheds burned by wildfires and prescribed fires were paired with control watersheds. Microbial NO{esc}b3{esc}p-{esc}s uptake rates were reduced significantly in soils burned by both wildfires and prescribed fires compared to their controls. There was no fire effect on gross nitrification rates in either fire types. The wildfires reduced gross NH{esc}b4{esc}s fluxes relative to controls, on the other hand, there was no such effect observed in soils burned by prescribed fires. Prescribed burns may not impact on soil N dynamics in the same magnitude as wildfires.;An effect of ash, a product of combusted organic matter and plant biomass, on N availability for understory vegetation post-fire was investigated at the Danskin Creek watershed where a wildfire burned a part of the watershed in August, 2002. Ash from burned and organic matter, a major source of ash, from adjacent unburned area were analyzed for their N properties. Ash loads were manipulated at three levels (i.e. double ash, control and no ash) two weeks after the fire. Foliage samples of understory vegetation were collected from the ash-manipulated plots in the following year to analyze N content and [delta]{esc}p15{esc}sN. Ash had lower N content, lower C:N ratio and higher [delta]{esc}p15{esc}sN than organic matter. The results of inferential statistics using linear mixed-effect ANOVA showed positive correlation between ash levels and foliar N content, and negative correlation between ash levels and foliar [delta]{esc}p15{esc}sN. Ash can be a significant N source for understory vegetation post-fire.
Thesis (Ph. D., Natural Resources)--University of Idaho, July 2007.
Major Professor:
Kathleen L. Kavanagh.
Defense Date:
July 2007.
Format Original:
xiii, 119 leaves :ill., maps ;29 cm.

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