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[1] We quantified the effects of repeated, seasonal fires on soil organic carbon (SOC), black carbon (BC), and total N in controls and four fire treatments differing in frequency and season of occurrence in a temperate savanna. The SOC at 0 - 20 cm depth increased from 2044 g C m(-2) in controls to 2393 - 2534 g C m(-2) in the three treatments that included summer fire. Similarly, soil total N (0 - 20 cm) increased from 224 g N m(-2) in the control to 251 - 255 g N m(-2) in the treatments that included summer fire. However, winter fires had no effect on SOC or total N. Plant species composition coupled with lower delta C-13 of SOC suggested that increased soil C in summer fire treatments was related to shifts in community composition toward greater relative productivity by C-3 species. Lower delta N-15 of soil total N in summer fire treatments was consistent with a scenario in which N inputs > N losses. The BC storage was not altered by fire, and comprised 13 - 17% of SOC in all treatments. Results indicated that fire and its season of occurrence can significantly alter ecosystem processes and the storage of C and N in savanna ecosystems.