Biodiversity change under human depopulation in Japan

What is it about?

Many countries are experiencing low human fertility leading to ageing and depopulation. Japan has been shrinking since 2010. Other Asian and European nations are following suit. We call Japan a Depopulation Vanguard Country for its world region of Northeast Asia. However, and despite some people's hopes for population decline to contribute to nature recovery -- what we call a “depopulation dividend” -- Japan’s experience shows this may not be happening. Our study used data collected by citizen scientists from 158 locations nationwide on behalf of Japan's Monitoring Sites 1000 project. Using this data we track biodiversity change among 466 species of birds, butterflies, fireflies, frog egg masses, and almost 3,000 native and non‑native plants across wooded, agricultural, and peri‑urban landscapes over 5–17 years. We found that biodiversity continued to decline regardless of whether human populations are shrinking or growing. Only areas with stable populations show more stable biodiversity. However, most of these areas are also ageing, making biodiversity decline likely in future when they too begin to depopulate. Our study points to agricultural land use change, including urban development, disuse and abandonment, and intensification, as the main driver of continuing biodiversity losses in these regions of Japan. This is probably due to the reduction and cessation of regular seasonal human livelihood practices and habitat maintenance, such as paddy flooding and rice planting and harvesting, that comes with the reduction and loss of a human presence. We urge countries facing depopulation to include consideration of its possible outcomes in their nature conservation and restoration programmes.

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Photo by Kouji Tsuru on Unsplash

Photo by Kouji Tsuru on Unsplash

Why is it important?

Our study has global importance for nature conservation and restoration because of: 1. Its empirical focus on depopulation and biodiversity. While many studies examine biodiversity loss under population growth, few investigate outcomes when populations shrink. This is the first large-scale, long-term study that uses citizen science to systematically track biodiversity trends in a country already in sustained demographic decline. 2. The nationwide, multi-species, multi-habitat dataset. Using data from over a decade of monitoring across 158 sites and a large number of species, the research moves beyond local case studies to provide statistically robust and generalisable findings for Japan, with similar implications for northeast Asia (South Korea, Northeast China, Taiwan). 3. Our challenge to the "depopulation dividend" hypothesis. The work directly tests, and largely refutes, the assumption that fewer people automatically leads to ecological recovery. The paper's findings have potential for reshaping nature conservation and restoration strategies in ageing and shrinking regions in many countries in Asia, and perhaps further afield. We urge policymakers to focus on active land-use management to promote biodiversity under depopulation. We position depopulation as a critical, urgent factor in global biodiversity policy, and demonstrate Japan's importance as a Depopulation Vanguard Country (DVC).

Perspectives