Ammonia fungi invade forest floors immediately after a enrichment disturbance by a large input of ammonium-nitrogen. Latent form(s) of the ammonia fungi are spores and/or mycelium fragments. Ammonia fungi are characterized by their rapid germination stimulated by the presence of ammonium-nitrogen under neutral to weakly alkaline conditions. Each ammonia fungus establishes its territory during suppressed combative abilities of other microbes following ammonium-nitrogen disturbance. Earlyphase ammonia fungi (EP fungi) quickly sporulate before nonammonia fungi colonize with the declining of ammonium- nitrogen concentration associated with descending pH. Ectomycorrhizal species of late-phase ammonia fungi (LP fungi) escape from the L-F horizon as a result of interactions between EP fungi and form mycorrhizae in the H-A horizon when other fungal activities are suppressed by the ammonium-nitrogen disturbance. Ectomycorrhizal ammonia fungi initially use ammonium-nitrogen when the pH rises because of the ammonium-nitrogen disturbance and then gradually utilize both ammonium- and nitrate-nitrogen when the effects of the ammonium-nitrogen disturbance weaken. Early-stage EP fungi are ruderal stress-tolerant strategists whereas late-stage EP fungi are combative ruderal strategists. LP fungi are combative strategists from the standpoint of the interactions between other ammonia fungi. This classification is based on differences in their respective propagation strategies.