Biodiversity change under human depopulation in Japan

Global studies consistently highlight a direct relationship between habitat and species losses, and human population and economic growth. Nevertheless, countries are experiencing below-replacement human fertility and starting to depopulate; among these countries, Japan is a global forerunner. To better understand whether human depopulation automatically yields environmentally restorative outcomes, we examine the impacts of human depopulation on aspects of biodiversity in Japan. Alongside population, land use and surface temperature, we analyse biodiversity change among 464 taxonomic species of bird, butterfly, firefly and frog egg masses, and 2,922 native and non-native plant species in wooded, agricultural and peri-urban landscapes across Japan over periods of 5–17 years from 2004. Irrespective of human population increase or decrease, biodiversity losses continue among most species studied mainly because of change in agricultural land use, either due to urbanization, disuse and abandonment, or intensification. Only where human numbers are currently stable, biodiversity is also more stable, although we anticipate that this may also change as ageing deepens into depopulation in these areas. We conclude by urging countries facing depopulation to account for its outcomes in their biodiversity conservation and restoration strategies.