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Since 1970, 73% of global wildlife has been lost, while the world's population has doubled to 8 billion. this isn't a coincidence but that population growth is causing a catastrophic decline in biodiversity.

Yet a turning point in human history is underway. According to UN projections, the number of people in 85 countries will be shrinking by 2050, mostly in Europe and Asia. By 2100, the human population is on course for global decline. this will be good for the environment.

In 2010, Japan became the first Asian country to begin depopulating. South Korea, China and Taiwan are following close behind. In 2014, Italy was the first in southern Europe, followed by Spain, Portugal and others. We call Japan and Italy "depopulation vanguard countries" on account of their role as forerunners for understanding possible consequences in their regions.

Given that depopulation could help deliver environmental restoration, we have been working with colleagues and to investigate whether Japan is experiencing what we have termed a biodiversity or something else.

Since 2003, hundreds of citizen scientists have been collecting biodiversity data for the Japanese government's project. We used 1.5 million recorded species observations from 158 sites.

These were in wooded, agricultural and (transitional spaces on the outskirts of cities) areas. We compared these observations against changes in local population, land use and surface temperature for periods of five to 20 years.

, published in the journal Nature Sustainability, includes birds, butterflies, fireflies, frogs and 2,922 native and non-native plants. These landscapes have experienced the greatest depopulation since the 1990s.

Due to the size of our database, choice of sites and the positioning of Japan as a depopulation vanguard for north-east Asia, this is one of the largest studies of its kind.

Japan is not Chernobyl

Biodiversity continued to decrease in most of the areas we studied, irrespective of population increase or decrease. Only where the population remains steady is biodiversity more stable. However, the population of these areas is aging and will decline soon, bringing them in line with the areas already seeing biodiversity loss.

Unlike in , where a sudden crisis caused an almost total evacuation which stimulated startling accounts of , Japan's population loss has developed gradually. Here, a mosaic pattern of changing land use emerges amid still-functioning communities.

While most farmland remains under cultivation, some falls into disuse or abandonment, some is sold for urban development or transformed into intensively farmed landscapes. This prevents widespread natural succession of plant growth or (planting of new trees) that would enrich biodiversity.

In these areas, humans are agents of ecosystem sustainability. Traditional farming and , such as flooding, planting and harvesting of rice fields, orchard and coppice management, and property upkeep, are important for maintaining biodiversity.

So depopulation can be destructive to nature. Some species thrive, but these are often non-native ones that present other challenges, such as the drying and choking of formerly wet rice paddy fields by invasive grasses.

Vacant and derelict buildings, underused infrastructure and socio-legal issues (such as complicated inheritance laws and land taxes, lack of local authority administrative capacity, and high demolition and disposal costs) all compound the problem.

Even as the number of akiya (empty, disused or abandoned houses) increases to nearly 15% of the nation's housing stock, the construction of new dwellings continues remorselessly.

In 2024, more than 790,000 , due partly to Japan's changing population distribution and household composition. Alongside these come roads, shopping malls, sports facilities, car parks and Japan's ubiquitous . All in all, wildlife has less space and fewer niches to inhabit, despite there being fewer people.

What can be done?

show deepening depopulation in Japan and north-east Asia. Fertility rates remain low in most developed countries. Immigration provides only a short-term softer landing, as countries currently supplying migrants, such as Vietnam, are also on course for depopulation.

Our research demonstrates that biodiversity recovery needs to be actively managed, especially in depopulating areas. Despite this, there are only a few in Japan. To help these develop, local authorities could be given powers to convert disused land into locally managed .

Nature depletion is a to global economic stability. Ecological risks, such as or , need better accountability from governments and corporations.

Rather than spend on more infrastructure for an ever-dwindling population, for example, Japanese companies could invest in growing local natural forests for .

Depopulation is emerging as a 21st-century global megatrend. Handled well, depopulation reduce the world's most pressing environmental problems, including resource and energy use, emissions and waste, and nature conservation. But it needs to be actively managed for those opportunities to be realized.

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