I examined the annual pattern of seed production in three Korean populations of Pinus densiflora from 1998 to 2002. During the fall season, data were collected on the numbers of cones per tagged tree, as well as seed counts, their mass, and seed set following dehiscence. Dbh was measured for individual trees during each spring. Overall, $80.3\%$ of the trees produced seed cones in even-numbered years compared with $51.6\%$ in odd-numbered years. Moreover, trees that matured seed cones in even years produced 12 times more seeds per tree than those in odd years. Tree diameters generally increased significantly during the summers after odd-numbered years, although the trees at one site showed a consistent growth rate each year after 2000. Annual variations in individual seed mass, seed set, and the proportion of damaged seed cones occurred largely within odd or even years. Based on these results, the following conclusions were made: 1) seed-cone production of P. densiflora is somewhat synchronized, but is not an all-ornothing phenomenon, 2) P. densiflora tends to undergo mast seeding at two-year intervals, and 3) this alternate-year excess in seed crop may have evolved to increase fitness, though the exact evolutionary mechanism is unclear.
