The role of seed dispersal and seedling traits in colonization and coexistence of Salix species in a seasonally flooded habitat

Abstract Regeneration traits of six co‐occurring Salix species were studied on a floodplain of the Sorachi River, central Hokkaido, Japan, and their colonization success and coexistence in a local habitat were discussed. Mixed Salix communities contained six Salix species; dominant: S. sachalinensis ; four subordinates: S. rorida, S. pet‐susu, S. miyabeana and S. subfragilis ; rare species: S. jessoensis . Their phenology, falling velocity and longevity of seeds, and the effects of microtopography and soil texture on seedling establishment were studied. The six Salix species had overlapped seed dispersal periods that coincided with the decrease of water level after a predictable spring flood. This coincidence was crucial for the colonization success because the seedlings were established on wet soils left by the decreasing water level. They showed two types of regeneration trait, specialization and generalization. S. rorida and S. subfragilis showed contrasting regeneration traits; early vs. late seed dispersal, large vs. small seeds, seedling distribution on coarse vs. fine soils, respectively. These two species rarely co‐occurred. On the other hand, the dominant S. sachalinensis had an intermediate seed size and dispersal timing, and a wide range of seedling distribution from coarse to fine soils. These results revealed that flooding seasonality influenced the colonization success together with the regeneration traits of Salix species, and that coexistence of the Salix species was facilitated primarily by regeneration niche separation related to flooding seasonality and soil heterogeneity.