Abstract

Ezo Deer as Indicators of Biodiversity Risk Hotspots: Long-term Evidence from the University of Tokyo Hokkaido Forest

G.G.T. CHANDRATHILAKE^1,2*, N. TANAKA¹, T. OWARI¹, T. KOBAYASHI¹N. OIKAWA¹

¹The University of Tokyo Hokkaido Forest, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Furano, Japan
²Department of Forestry and Environmental Science, University of Sri Jayewardenepura, Sri Lanka
^*thilakawansha@sjp.ac.lk

 The Ezo deer (Cervus nippon yesoensis), a native sika deer subspecies in Hokkaido, Japan, is an integral component of forest ecosystems; however, population increases have intensified pressure on forest regeneration, agricultural interfaces, and biodiversity conservation. As biodiversity credit and nature-positive frameworks require quantifiable, spatially explicit indicators of ecological risk and management effectiveness, long-term wildlife monitoring data provide a critical evidence base. This study analyzed annual light-census surveys conducted each October (mating season) from 2007 to 2025 along fixed routes in the University of Tokyo Hokkaido Forest (UTHF). Encounter rate (individuals km⁻¹ night⁻¹) was used as an index of relative abundance to evaluate temporal trends, habitat associations, demographic structure, and management-relevant spatial patterns. Mean encounter rates exhibited a significant non-linear (quadratic) temporal pattern (p = 0.045), while no significant linear increase or decrease was detected over the study period (p = 0.293), indicating long-term population persistence rather than directional change. Deer occurrence differed strongly between habitat types, with significantly higher encounter rates in farmland-associated routes (mean = 5.31) compared with forest stands (mean = 1.65; p = 0.001). To translate abundance patterns into a management-relevant metric, a relative biodiversity risk index was defined as encounter rate multiplied by a habitat weighting factor (1.5 for farmland, 1.0 for forest), reflecting heightened ecological and socio-ecological sensitivity at forest–agriculture interfaces. Route-level analysis revealed pronounced spatial heterogeneity, with a single farmland-associated route accounting for the highest cumulative abundance (1,585 individuals) and risk index. Demographic structure remained stable over time, and recruitment was not correlated with annual population change (r = 0.052). These findings demonstrate how standardized long-term monitoring can support biodiversity credit design, spatial prioritization, and adaptive management, highlighting the importance of targeting high-risk interface areas to advance nature-positive outcomes.