Comparable biodiversity and demographic structure between sacred groves and protected forests with Dipterocarpus hasseltii reveal conservation value of customary forests in Bali, Indonesia

Sacred groves are natural forests that are managed by local communities to support their cultural and religious practices. These forests are often refugia to threatened species and crucial nodes of biodiversity in an increasingly human-dominated landscape. In Asia, conservation evidence of sacred groves is often geographically limited to a few overrepresented countries. Here, we present the first empirical study on the tree communities in sacred groves in Bali, Indonesia, and compare them to formally gazetted protected forests without a sacred status. Specifically, we measured the diversity, basal area and density of tree species from three ontogenetic stages (adults, saplings, and seedlings) in sacred groves and protected forests that contain Dipterocarpus hasseltii, a globally Endangered dominant canopy tree species of local cultural significance. Our results showed that sacred groves and protected forests with D. hasseltii populations had similar levels of tree species richness, diversity, and density of saplings and seedlings. The density of D. hasseltii individuals and the basal area of all species of adult trees was higher in sacred groves than in protected forests, potentially due to culturally-driven active protection of D. hasseltii and large, old trees in the sacred groves. Taken together, our findings demonstrate that local community’s involvement in forest governance had a positive impact on biodiversity conservation that was comparable to protected forests. Despite sacred groves being invaluable localities for in-situ conservation of threatened tree species, incorporation into existing protected area network could diminish the autonomy and traditions of the local communities. Therefore, our study provides crucial evidence of the circumstances under which customary forests balanced both natural resource use and biodiversity conservation. This lends support to Indonesia’s forest decentralization policies through which local communities can maintain stewardship over biodiversity-rich customary forests.