Determinant factors in the seedling establishment of Pasania edulis (Makino) Makino

Pasania edulis (Makino) Makino is one of the dominant Fagucea tree species in evergreen broad-leaved forests in southern Japan, and its regeneration success may have a major impact on the dynamics of evergreen broad-leaved forests. We conducted a field survey on the population process from acorn production to seedling establishment of P. edulis in an evergreen broad-leaved forest in Kagoshima, southern Japan, from 1995 to 2009. The acorn crop varied greatly among the 14 cohorts, with mast cropping being recorded every 3-4 years. The mortality rate of acorns was very high for all 14 cohorts (99.3-100 %). Important mortality factors were failure to mature (empty acorns), attack by Curculio weevil on trees, predation of dropped acorns by Apodemus mice and large or medium-sized mammals (wild boar (Sus scrofa leucomystax), badger (Meles meles anakuma), and raccoon dog (Nyctereutes procyonoides viverrinu)), and attacks on germinated acorns by the acorn borer (Coccotrypes graniceps). Among these factors, predation by Apodemus mice was the greatest contributor to annual fluctuations in total mortality until seedling establishment. Large or medium-sized mammals and the acorn borer also caused severe damage to dropped acorns in some years, but contributed little to annual fluctuations in total mortality. For successful regeneration, mast cropping was essential. However, a small population of Apodemus mice, that is, a low predation pressure, was also required during mast years.