Long-term data is essential to understand the dynamics of avian seed dispersal because the pattern has large annual variation. We investigated annual variation of seed dispersal pattern by using long term data of bird-dispersed tree, Swida controversa. Field investigation was conducted at Ogawa Forest Reserve, Central Japan. Bird-dispersed seeds have been retrieved every two weeks by >100 seed traps for 22 years. Fruit consumption by birds was directly observed for three years. Many factors showed large annual variations (seed production, 0.0-219.5 seed /m²; peak of removal, Jul. 23-Oct. 20; mean dispersal distance, 1.6-21.7 m; removal rate, 0.05-0.70). Dispersers also varied annually as the result of bird migration and fruit phenology. In the years when peak of removal was late, dispersal distance increased and removal rate by birds decreased. In the years when seed production was large, seed removal rate decreased. Thus, rate and distance of dispersal, which are the important factors of seed dispersal effectiveness, are explained by seed production and seed removal phenology. The results suggest that spatial and temporal variation of fruits and dispersers determine the seed dispersal pattern and effectiveness.