During the summer of 2003 we identified seven sites in wilderness areas of the Inland Northwest that represent stands exposed to fire 0, 1, 2 or 3 times in the last 120 years.  The sites with multiple fires represent a fire return interval similar to what is thought to be natural in ponderosa pine ecosystems.  Mineral soil samples were collected from each of the seven sites and analyzed for total C and N, potentially mineralizable N (PMN), NH₄⁺, and NO₃^-.  A subset of five sites were selected, resampled and analyzed for net nitrification, gross nitrification, nitrification potential (aerated slurry assay), and resin sorbed nitrate (as a measure of in-situ nitrification). Nitrifier community analyses were conducted on soils from two sites using polymerase chain reaction (PCR) and primer sets specific for the ammonia monooxygenase gene (amoA) or 16S rDNA for ammonia oxidizing bacteria. The community structure was analyzed by using denaturing gradient gel electrophoresis and abundance was examined using quantitative PCR. Fire intervals had no influence on extractable NH₄⁺, and NO₃^- in soil grab samples; however, stands exposed to multiple burns had significantly greater presence of nitrifying organisms, higher rates of potential nitrification and greater gross and net nitrification.  Natural fire return intervals reduce total N capital, but increase nitrification and nitrifier activity.