Active management for mitigating decline of native species diversity in an urban shrine forest in western Japan

Shrine forests in Japan represent traditionally preserved natural areas and could potentially serve as centers for biodiversity conservation in urban areas. Shrine forests are managed to meet social needs, which can conflict with conservation efforts. Here, we aimed to quantitatively assess the long-term effects of active forest management on vegetation dynamics in an urban shrine forest, and to evaluate strategies for balancing biodiversity conservation with social needs. As a case study, we analyzed vegetation dynamics in the forest at Nishinomiya Shrine, designated natural heritage of Hyogo Prefecture, Japan. Species composition, stem density, basal area, and relative growth rates were assessed across four survey years (2003, 2008, 2015, 2020). The effects of a 4-m wide clear-cut buffer zone along the western forest edge, as well as enrichment planting in the forest interior, were evaluated using community ecology analyses including diversity indices, vegetation similarity, and nMDS ordination. Following the removal of invasive Trachycarpus fortunei in 2005, stem density of native species increased and forest composition approached that of a late-successional lucidophyllous forest. However, exotic and ornamental species such as Ligustrum lucidum and Euonymus japonicus subsequently increased, particularly after 2015, exhibiting higher relative growth rates than native species. We estimated that establishing a 4-m wide clear-cut edge to avoid conflict with neighboring properties, would remove approximately 7% of exotic and ornamental species with minimal impact on native biodiversity, and that enrichment planting could compensate for biodiversity loss in the buffer zone. Although initial restoration efforts were successful, the recent increase in exotic and ornamental species suggests ongoing diverted succession, highlighting the need for continuous, active management of urban shrine forests guided by quantitative assessment of vegetation dynamics.