Abstract: The accumulation and biological cycling of nitrogen of the 16 year old alder and cypress mixed forest have been studid in Yanting county,Sichuan province.The results showed that the amount of nitrogen in the standing biomass of the community was 533.98 kg穐a^-1 of which the amounts of aboveground and underground parts were 468.48 kg穐a^-1 and 55.50kg穐a^-1 respectivly.With regard to the biological cycling of nitrogen in the community,the value of annual uptake was 110.36kg穐a^-1 of which its retention was 23.45kg穐a^-1 and the return was 86.91 kg穐a^-1 per year.The turnover period was 6 years.The nitrogen cycling of the community was charaterized by large uptaking much returning and rapid turnover.

Key words: forest fire severity, normalized burn ratio (NBR), environmental factor, burnt area, remote sensing, Huzhong forest region of Great Xing’an Mountains.