There is an inextricable link between biological and cultural diversity, captured in the concept of biocultural diversity, whereby the former (genes, species, and habitats) co-adapt with the latter (knowledge, values, beliefs, practices and institutions). Sacred natural sites are increasingly considered showcases for the conservation of biocultural diversity, because their strong cultural importance derives from, and requires maintenance of, biodiversity. The research described in this paper is concerned with the conservation of the threatened "yellowwood" tree (Afrocarpus falcatus) in sacred natural sites of Sidama, southwest Ethiopia. Mixed methods were used to document types of sacred forests sites and the extent and distribution and dominance of A. falcatus in these, to identify drivers of endangerment of A. falcatus and other native woody species in Sidama, Ethiopia and to understand local explanations for the importance and maintenance of these sites. The results suggest that species such as A. falcatus owe their continued existence to resilience of ancestral tree-based rituals within informal protection areas and at homesteads and communal areas. Thus, the maintenance of an ancestral value