Wednesday, 9 November 2005 - 2:45 PM
289-7

Effect of prescribed fire on soil organic matter in a ponderosa pine forest.

Jeff Hatten and Darlene Zabowski. University of Washington, College of Forest Resources, Seattle, WA 98195-2100

Fire consumes and alters organic material, these changes may impact soil organic matter (SOM). Residues of un-burnt organic material (char, charcoal, and soot, i.e. black carbon) are left behind after fire at the same time humified SOM is altered through pyrolysis. The magnitude of change SOM experiences due to a prescribed fire may be affected by the season in which it is burned and the number of burns conducted. The objective of this study was to determine if soil organic matter is affected by spring and fall burning, at 5 and 15 year burn intervals, in a ponderosa pine forest of the southern Blue Mountains of eastern Oregon. Soil horizon depths were measured, and samples collected by major genetic horizons. Samples were analyzed for pH, C, N, C/N ratio, loss on ignition, fulvic acid, humic acid, and humin. Using two-factor ANOVA results to date show differences in soil organic matter between the plots with fire and the control. Minimal differences have been found between the plots with fire. Spring and fall burns may not have been able to affect SOM differently because they may have burned at similar intensities.

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