Female and male individuals of a sexually dimorphic species may interact differently with heterospecific individuals. However, evidence demonstrating such phenomena remains scarce. This study explored relationships between sexual dimorphism and ecological communities, focusing on the dioecious plants Eurya japonica Thunb. and Eurya emarginata (Thunb.) Makino. The results showed that sexual dimorphism in floral traits exerted significant effects on the behavior of flower-visiting flies, bees, and other insects, as well as the survival, growth, and oviposition behavior of flower-feeding moths, and the abundance and community structure of nectar-inhabiting bacteria and yeasts. These effects on insects and microbes may in turn affect the evolution of floral traits and plant reproductive success. These findings demonstrate the wide-ranging effects of sexual dimorphism in ecological communities.

We investigated the regeneration dynamics of a small, fragmented stand of Siebold’s beech (Fagus crenata) at Gofukuji Temple in Matsumoto, central Japan, in terms of stand structure and long-term seed production. The stand was 0.555 ha in area, and the total basal area of trees ≥3 m in height was 66.15 m²/ha. The stand was dominated by three species: Japanese red pine (Pinus densiflora; 48.2% of the total basal area); Siebold’s beech (22.0%); and Jolcham oak (Quercus serrata; 18.0%). Pines showed a broad range of diameter at breast height (DBH) values, at 25–85 cm, whereas oaks and beeches had unimodal and L-shaped DBH distributions that peaked at 25–30 and 95 cm, respectively. Only one beech individual was found in the understory (height: 0.5–3 m), which suggests poor regeneration, likely due to past suppression by dense dwarf bamboo (Sasa borealis) cover and ongoing sika deer (Cervus nippon) browsing. Among saplings (height：<0.5 m), oaks (Q. serrata and Quercus crispula) were widespread (density: 0.47 individuals/m²), whereas beech saplings were limited to 30% of the stand area (density: 0.0176 individuals/m²) and mainly aged ≤8 years, and red pine saplings were rare. An analysis of long-term seed monitoring data (2005–2024) detected no mast years and only two moderate seed crops. These results are consistent with previous genetic studies of this fragmented population in suggesting reduced seed viability due to inbreeding and pollen limitation. Given the pine population decline, likely caused by pine wilt disease, and the extremely poor beech regeneration in this stand, oak species may become dominant in the future, although continued deer browsing could eventually suppress forest regeneration overall.