Yoh Iwasa

Evolution of masting -- synchronized and intermittent reproduction of trees

Yoh Iwasa

Department of Biology, Kyushu University



Trees in mature forests often show intermittent reproduction (masting), synchronized over a long distance. According to the dynamics of the resource reserve of individuals, trees can show a large between-year fluctuation in the seed crop even in a constant environment. Reproduction of different trees may be synchronized if fruit production is limited by the availability of outcross pollen. We study conditions for masting to evolve. Assumptions are: the forest consists of many sites, each occupied by a single canopy tree. After a canopy tree falls, the vacant site (gap) becomes available for recruitment., We first show that masting never evolves if all vacant sites are filled by individuals from seeds produced in the same year. Then we demonstrate that masting can evolve if some seedlings survive for several years, forming a seedling bank on the forest floor, where seeds produced in different years compete for gap acquisition., We also study the effect of specialist seed predators. In the complete absence of seeding bank, masting never evolves even in the presence of seed predators. If seedling survivorship is positive but small, then the presence of seed predators can promote the evolution of masting.