Recently in Japan, cases of deer, bears, and wild boars appearing in towns, consuming crops, and even attacking people have significantly increased. This is not limited to remote areas like the Central Alps in Japan; rather, wars with wildlife are frequently occurring in popular tourist destinations such as Hokkaido and Kyushu. In 2023, the number of bear attacks on humans reached an all-time high. In response to the increasing damages, the Japanese government is preparing a revision of the wildlife protection laws to relax the conditions for firearm use and is approaching a resolution in the National Diet.
Animal scientist Baek Seung-yoon, a postdoctoral researcher at Tokyo University of Agriculture and Technology, said, "As global warming and population decline expand the distribution of large mammals, the potential for conflict between humans and animals is growing."
A research team led by Baek and his mentor, Koike Shinsuke, a professor at Tokyo University of Agriculture and Technology, published research results last month on the expansion of habitats for large mammals in Japan due to climate change and population decline in the international academic journal Communications Earth and Environment. Baek participated as the first author and corresponding author.
Globally, as human living areas expand, the habitats and distributions of large mammals are decreasing. However, in some areas, the opposite is true, with populations and habitats of large mammals increasing. In Japan, habitats for large mammals have also increased in the last 40 years.
According to Baek, large mammals in Japan once disappeared as industrialization and urbanization progressed. However, over the past 40 years, the activity ranges of large mammals such as wild boars, Asiatic black bears, mountain goats, Japanese macaques, sika deer, and brown bears have rapidly increased. During autumn years when acorns and other food sources are scarce, the likelihood of large mammals like Asiatic black bears appearing also rises.
Using data collected over 40 years, Baek analyzed which factors influenced the changes in the distribution of large mammals. The research team analyzed habitat distribution data for Asiatic black bears and wild boars from 1978, 2003, and 2014, and for Asiatic black bears, macaques, and brown bears from 2017.
Baek noted, "These animals were said to live in the mountains 40 years ago, but now they can be easily found where people reside." In fact, the distribution of large mammals in Japan has rapidly expanded over the past 40 years. During this time, the habitats of deer increased by 2.6 times, wild boars by 1.9 times, Asiatic black bears by 2.0 times, mountain goats by 2.1 times, Japanese macaques by 2.1 times, and brown bears by 1.9 times.
Deer are expanding their habitat by 174.9 square kilometers annually, to the point where there are now no regions they do not inhabit. Wild boars have expanded their habitat distribution in western Japan, and while brown bears are expanding their habitat more slowly, averaging 35.2 square kilometers per year, they are currently found in 80% of Hokkaido.
To precisely understand why mammal habitats have expanded, the research team divided Japan into small areas of 5 kilometers by 5 kilometers. They then examined how factors such as land usage, terrain, snowfall, human activities (night lighting), abandoned farmland, and propagule pressure influenced these changes.
These factors have indeed contributed to the recent expansion of habitats for large mammals.
From 1978 to 2003, deer, wild boars, Asiatic black bears, and mountain goats in Japan showed a tendency to expand their habitats into regions with fewer human activities (night lighting) and more abandoned farmland across Honshu, Kyushu, and Shikoku. In contrast, brown bears exhibited a reverse pattern, aiming to expand into areas with more farmland during the same period.
However, since the 2000s, large mammals have shown a strong tendency to expand their distribution into regions with more farmland. They have also tended to extend their habitats to areas with less snowfall and closer proximity to previously inhabited locations.
Baek finds the rapid expansion of wildlife habitats can be traced back to population decline and global warming. Like Korea, Japan is facing severe low birthrate and aging issues, and as the rural population decreases, abandoned farmland continues to increase. It is analyzed that as large mammals expand their living areas into these abandoned rural areas, the contact and conflicts with humans are rising. Trends have also been confirmed, indicating that habitats have expanded into high-latitude and high-elevation areas where snow has decreased due to global warming.
Baek emphasizes a desire to focus on coexistence rather than conflict between humans and animals. He stated, "As the density of large wildlife increases, the area of contact with humans grows, leading to increased conflicts and a higher risk of zoonotic diseases. To counter changes brought about by global warming and population decline, it is necessary to maintain a proper distance and systematic management between humans and large mammals."
This study has garnered attention from the Japanese media as it is a rare research effort examining the causes behind the increasing appearance of wildlife, a rising social issue in Japan, using long-term records spanning 40 years. The fact that a young scientist from Korea is leading wildlife research in Japan also draws attention.
Baek graduated from Jeju National University with a degree in biology and then moved to Japan, where he earned his master's and doctorate at Tokyo University of Agriculture and Technology. Interested in bear research, he has accumulated substantial data on bear habitats and large mammals in Japan and continues his studies. On the day of the interview, he mentioned he was "on his way back from a field survey."
- It seems the Japanese media is also quite interested in this research.
"Recently, bears or deer are frequently becoming social issues in Japanese society. News of bears coming down from the mountains and injuring elderly individuals is emerging, and the problems related to population decline and global warming due to aging are also topics of interest in Japanese society."
- What led you to study wildlife in Japan?
"Originally, I was conducting research on tracking Asiatic black bears with GPS devices to monitor their activities and behavior. The Asiatic black bears in this study are of the same species as those in Korea. They are distributed over a wide area from West Asia to Siberia, but most are in a state of extinction. In contrast, Japan has a relatively abundant population, capturing thousands of Asiatic black bears annually. There is also a wealth of research data, so I thought that learning here would allow me to contribute significantly to the conservation of Korea's Asiatic black bears in the future."
- Are the habitat environments in Korea and Japan very different?
"Both Korea and Japan are experiencing urbanization and aging. However, Korea has a higher road density, leading to significant habitat fragmentation, making it a challenging environment for large mammals. Japan, too, witnessed a significant decline in large mammals due to hunting and land clearing from the 18th to 19th centuries. However, with the recent population decline in rural areas, houses disappearing, and agricultural and hunting activities declining, the preferred ranges for animals have expanded. Thus, Japan's habitat environment is somewhat better than in Korea."
- It seems that the habitats of large mammals have changed over the past 40 years.
"Although there are some differences by period and species, until 20 years ago, wildlife generally avoided areas with high levels of human activity. They tended to move toward areas with less cultivation. However, in the past 20 years, wildlife have begun to expand their activity ranges toward locations with more cultivation. Of course, these are agricultural lands, but they are areas with many abandoned farmlands. A trend of expanding habitats into regions with less snowfall has also been confirmed."
- Recently in Japan, stories like 'a bear has eaten a person' and 'a monkey has attacked a person' are frequently heard. What animals are causing trouble?
"Mainly deer, wild boars, and bears. In 2023, bear-related incidents increased significantly. However, the primary problem is with deer, as they are causing severe crop damage. This species, originally found in Korea, is known as the sika deer. While the Korean water deer tends to be selective about its food, these deer consume the fruits and crops around them indiscriminately. They eat in large quantities, leading to the degradation of the forest's vegetation. By consuming trees and plants at the bottom of the mountain, they even trigger landslides and impact the breeding of birds and insects."
- The Asiatic black bear is a protected species in Korea, but in Japan, it seems to be regarded as a nuisance.
"Surprisingly, many people do not realize that Asiatic black bears live in Japan. Even at international conferences, many scholars are unaware of their presence in Japan. In reality, only brown bears inhabit Hokkaido, while Asiatic black bears primarily reside in the regions below. Unlike Korea and other habitats, the Asiatic black bear is relatively common in Japan. There are many incidents where people get hurt or even killed by their attacks. As the recent incidents have increased, there is a trend towards easing the restrictions on capturing bears. Currently, about 3,000 to 5,000 bears are captured annually."
- Is the lack of predators making it difficult to control their populations?
"Many see it that way. Japan once had wolves, the ultimate predator. After the only species that could pressure deer vanished, only the Asiatic black bear and brown bear remain as apex predators in Japan. However, the Asiatic black bear primarily feeds on vegetation, so it does not exert any effective pressure on deer populations."
- Between global warming and population decline, which factor has a greater impact on the expansion of wildlife habitats?
"It is difficult to say which comes first. Like humans, animals prefer to be in more favorable living conditions. In the process, they are coming closer to humans. It is evident that human activities have greatly restricted animal movements. If population decline continues, it will open more space for wildlife to operate and expand. As global warming persists, less snow will fall in higher mountainous or colder regions. This will promote the growth of grasses and trees that serve as food, making it easier for animals to move around."
- If the habitats of large mammals continue to increase, will conflicts be inevitable?
"In Japan, the approach is currently focused on preserving wildlife while mitigating issues. First, the population is controlled, and compensation is provided when issues arise. Finally, they are searching for ways to manage habitats to prevent problems from occurring. Recently, they are considering the concept of zoning, where they define areas for wildlife, human habitation, and a buffer zone in between. Then, in the buffer zone, wildlife can only be trapped when they cause problems, while a strict catch policy is applied in human habitation areas."
- Why is it necessary to maintain distance from wildlife?
"Increased contact with wildlife can lead to the spread of infectious diseases like COVID-19. I understand that chronic wasting disease (CWD), known as deer mad cow disease, is currently spreading in the United States, which is a serious issue. Living in close proximity to wildlife increases the chances of zoonotic diseases spreading. This is necessary for coexistence. As the conflicts between animals continue as they do now, it is undesirable for negative perceptions about needing to eliminate them to spread."
- Should we not worry in Korea?
"The situations are different, but more research is needed in this area. Korea still tends to focus more on wildlife conservation. However, as wildlife gradually expands their distribution ranges and recovers habitats, similar situations are likely to occur. Korea is also experiencing population decline in rural areas. As the number of people living in the countryside decreases and their activities decline, it becomes easier for animals to come closer."
- What is your next research topic?
"The biggest concern is how humans and animals will continue to coexist as population decline and global warming persist. Some regions are already attempting zoning. It is necessary to verify whether these efforts are effective. Our research does not aim to view these changes negatively. The goal is to seek coexistence with large mammals. When conflicts arise between humans and animals, negative perceptions will increase, and the belief that animals that have returned to nature should once again be eliminated will spread. Understanding the mechanisms and ecology of how the habitats of large mammals expand and assisting in their proper management is at the core of our research for coexistence."
References
Communications Earth&Environment(2025), DOI : https://doi.org/10.1038/s43247-025-02261-w