At a Glance
- A surprising new study reveals that Japan’s declining human population is linked to a continued loss of biodiversity, challenging the idea that fewer people automatically help nature.
- Researchers analyzed over 1.5 million citizen-science observations, tracking hundreds of species alongside changes in land use and human population data across the country.
- The primary driver of species loss is the changing use of agricultural land through abandonment or urbanization rather than the direct effect of a shrinking population.
- Historic, human-managed agricultural practices that once supported rich ecosystems are disappearing, causing environmental degradation and accelerating the decline of wildlife in rural areas.
- Japan’s experience serves as a critical warning for dozens of other European and Asian countries that are also projected to face significant depopulation in the coming decades.
A new international study challenges the assumption that a shrinking human population automatically leads to environmental recovery. Research published in the journal Nature Sustainability reveals that in Japan, a country at the forefront of global depopulation, the decline in human numbers coincides with a continued loss of biodiversity. Biodiversity, which refers to the variety of all living things in a particular area, is not rebounding as expected. Instead, the study suggests that humans are abandoning or changing agricultural land, creating new pressures on ecosystems. This trend could soon be seen in dozens of other countries facing similar demographic shifts.
A team of researchers from the University of Sheffield in the United Kingdom and Tokyo City and Kindai universities in Japan conducted a massive analysis to understand this complex relationship. They combined human population, land use, and temperature data with over 1.5 million biodiversity observations collected by citizen scientists across Japan over five to 17 years. The impressive dataset tracked changes among 464 species of birds, butterflies, and fireflies, as well as frog egg masses and nearly 3,000 native and non-native plant species in wooded, agricultural, and developing peri-urban landscapes.
The findings showed that biodiversity losses continued for most species studied regardless of whether a region’s population was growing or shrinking. The primary cause was not the number of people but the changing agricultural land use. Some farmland was lost to urbanization as people left rural areas, while others were abandoned. This disuse disrupts the delicate balance of ecosystems historically supported by traditional farming practices like managing rice paddies and forests. Kei Uchida, an associate professor at Tokyo City University, notes that these human activities had “shaped and supported ecological richness for centuries.” However, their abandonment is now undermining the biodiversity they once sustained.
Researchers warn that Japan is a “Depopulation Vanguard Country,” offering a preview of what may happen in other nations. With the United Nations projecting that 85 countries will be depopulating by 2050, the lessons from Japan are globally significant. The study highlights that spontaneous “rewilding”—the idea that nature will recover once people leave—is not a guaranteed outcome. The authors urge governments in countries with falling birth rates, including those in East Asia and Southern and Eastern Europe, to develop proactive conservation strategies that account for the environmental consequences of depopulation and carefully manage the transition of rural landscapes.
References
- Uchida, K., Matanle, P., Li, Y., Fujita, T., & Hiraiwa, M. K. (2025). Biodiversity change under human depopulation in Japan. Nature Sustainability. https://doi.org/10.1038/s41893-025-01578-w
- University of Sheffield. (2025, June 12). Japan’s shrinking rural population linked to ongoing biodiversity losses, study shows. Phys.Org; University of Sheffield. https://phys.org/news/2025-06-japan-rural-population-linked-ongoing.html
