Long-term nucleation effect of remnant trees in a temperate forest established on abandoned grassland

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The contribution of seed dispersal by animals in a 25-year-old forest established on abandoned temperate grassland was investigated, with a focus on the long-term nucleation effect of scattered remnant trees. The remnant trees were found to increase the density and species richness of zoochorous trees around them, leading to local heterogeneity in the stand structure. However, this effect was not found for barochorous and anemochorous trees. Although the contribution of nucleation to the initial process of forest regeneration has often been recognized in the tropics, this study confirmed that the nucleation effect occurs even in temperate regions, and the effect persisted long after the forest was established. However, we detected the long-term nucleation effect only for zoochorous tree species, indicating that the perch effect was the main contributor to nucleation at the study site. Zoochorous trees that regenerated around the remnant trees were relatively small and confined to the shrub layer of the established forest. It is possible that either the regeneration of zoochorous tree species was delayed compared with that of trees with other seed dispersal modes or the zoochorous tree species were outcompeted by other vegetation because of their slow initial growth. The long-term nucleation effect was unclear when all the trees, including anemochorous and barochorous trees, were analyzed. This was probably due to the broad range of many non-zoochorous trees away from the canopy of the remnant trees in the study area, masking the nucleation effect on the smaller number of zoochorous trees.