Fire effects on nitrogen pools and dynamics in terrestrial ecosystems: A meta-analysis

A comprehensive and quantitative evaluation of the effects of fire on ecosy stem nitrogen (N) is urgently needed for directing future fire research and management. This study used a meta-analysis method to synthesize up to 185 data sets from 87 studies published from 1955 to 1999. Six N response vari ables related to fire were examined: fuel N amount (FNA) and concentration (FNC). soil N amount (SNA) and concentration (SNC). and soil ammonium (NH4- ) and nitrate (NO3-) pools. When all comparisons (fire treatment vs. contro l) were considered together, fire significantly reduced FNA (58%), increase d soil NH4+ (94%) and NO3- (152%), and had no significant influences on FNC , SNA, and SNC. The responses of N to fire varied with different independen t variables, which were vegetation type, fire type, fuel type, fuel consump tion amount, fuel consumption percentage, time after fire, and soil samplin g depth. The response of FNA to fire was significantly influenced by vegeta tion type. fuel type, and fuel consumption amount and percentage. The reduc tion in FNA was linearly correlated with fuel consumption percentage (r(2) = 0.978). The response of FNC to fire was only affected by fuel type. None of the seven independent variables had any effect on SNA. The responses of SNC, NH4+, and NO3- depend on soil sampling depth. The responses of both NH 4+ and NO3- to fire were significantly affected by fire type and time after fire but had different temporal patterns. The soil NH4+ pool increased app roximately twofold immediately after fire, then gradually declined to the p refire level after one year. The fire-induced increase in the soil NO3- poo l was small (24%) immediately after fire, reached a maximum of approximatel y threefold of the prefire level within 0.5-1 year after fire, and then dec lined. This study has identified the general patterns of the responses of e cosystem N that occur for several years after fire. A key research need rel evant to fire management is to understand how the short-term responses of N to fire influence the function and structure of terrestrial ecosystems in the long term.