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

A comprehensive and quantitative evaluation of the effects of fire on ecosystem 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 variables 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. control) were considered together, fire significantly reduced FNA (58%), increased 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 independent variables, which were vegetation type, fire type, fuel type, fuel consumption amount, fuel consumption percentage, time after fire, and soil sampling depth. The response of FNA to fire was significantly influenced by vegetation type. fuel type, and fuel consumption amount and percentage. The reduction 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 NH4+ and NO3- to fire were significantly affected by fire type and time after fire but had different temporal patterns. The soil NH4+ pool increased approximately twofold immediately after fire, then gradually declined to the prefire level after one year. The fire-induced increase in the soil NO3- pool was small (24%) immediately after fire, reached a maximum of approximately threefold of the prefire level within 0.5-1 year after fire, and then declined. This study has identified the general patterns of the responses of ecosystem N that occur for several years after fire. A key research need relevant 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.