The Chornobyl Exclusion Zone as a wildlife refuge: restricted human access shaped mammal recolonization

Land-use changes and habitat degradation threaten biodiversity and ecosystem functions globally. Large terrestrial mammals are particularly vulnerable due to low reproductive rates, large spatial requirements and sensitivity to human disturbances. Increasing coverage and effectiveness of protected areas (PAs) is vital to conserve mammal species and their habitats. We used camera trapping to assess the impact of human activities and landscape characteristics on diversity, occupancy and detection probabilities of 11 terrestrial mammals in northern Ukraine in 2020-2021. We evaluated the impact of human stressors and landscape modifications on species diversity, occupancy and detection probabilities across the Ukrainian Chornobyl Exclusion Zone (CEZ), regional PAs and non-PAs. We implemented hierarchical Bayesian single-species single-season occupancy models to identify the covariates that described the occupancy (Ψ) and detection (p) probabilities for each species. Species diversity, occupancy and detection probabilities were significantly higher in the Ukrainian CEZ and neighbouring Drevlianskyi Nature Reserve (highest occupancy probabilities of Przewalski's horse, Eurasian lynx, moose and red deer) than in all other areas. PA coverage positively influenced red deer, red fox and raccoon dog occupancies, while PA protection status showed mixed effects across species. Our results demonstrate that PAs are most effective when they are large, contiguous and human access restrictions are actively enforced.