2025 Volume 50 Issue 4 Pages 279-287
A comprehensive census of adult trees complemented by a density survey of seedlings and juvenile individuals was conducted within the Podocarpus macrophyllus forest on a sand spit in the western Izu Peninsula. In total, 225 adult P. macrophyllus trees were identified, which demonstrated no significant change in population since their designation as natural monuments in 1980. However, majority of the trees were in subtree layer (58.5%). Only 31.6% were tall trees that reached the upper layers of the forest canopy. Cinnamomum camphora, a co-occurring species, were mostly large-diameter tall trees, indicating a shift in dominant species. While P. macrophyllus trees which have shade tolerance currently exhibit no significant health decline despite the presence of C. camphora. Pinus thunbergii was characterized by the presence of numerous large-diameter tall trees, which preferentially occupied the sea-facing regions. In contrast, P. macrophyllus displayed a preference for interior habitats. The seedling density of P. macrophyllus exhibited high variability across sites with 7–431 seedlings per 100 m2. It is worth noting that the majority of seedlings were typically <20 cm tall. Relative light intensity in the forest was low, averaging 2.6% at 100 cm above ground level, and the scarcity of young P. macrophyllus exceeding 100 cm in height suggests a low rate of regeneration within the forest. The Polysticho-Machilus thunbergii community was established on a nearby sandbar, and many species commonly occur on the forest floor with this P. macrophyllus forest.
