Recently in Japan, the number of cases where deer, bears, and wild boars appear in villages, devouring crops and even attacking people, has notably increased. Not only in remote areas like the Central Alps of Japan but also in places like Hokkaido and Kyushu, which are frequently visited by Korean tourists, conflicts with wildlife are becoming common. In 2023, the number of bear attacks on people reached a record high. As damages increase, the Japanese government is preparing to amend the wildlife protection law to relax conditions for firearm use and is poised for a National Assembly resolution.
Seung-Yoon Baek, a postdoctoral researcher (assistant professor) at Tokyo University of Agriculture and Technology, noted that "as global warming and population decline expand the distribution of large mammals, the potential for conflict between humans and animals over space is growing."
The research team led by Baek and his graduate advisor, Shinsuke Koike of Tokyo University of Agriculture and Technology, published findings last month in the international journal Communications Earth & Environment. The study revealed that the habitats of large mammals in Japan are expanding due to climate change and population decline. Baek participated as the first author and corresponding author in this research.
As human living spaces expand globally, the habitats and distribution of large mammals are decreasing. However, in some areas, the population and habitat of large mammals are increasing. In Japan, the habitat of large mammals has increased over the past 40 years.
According to Baek, Japan once saw its large mammals disappear as industrialization and urbanization progressed. However, in the last 40 years, the activity range of large mammals such as wild boars, Asiatic black bears, goats, monkeys, sika deer, and brown bears has rapidly expanded. In years with a shortage of food, such as acorns in autumn, the likelihood of large mammals like the Asiatic black bear appearing also increases.
Baek analyzed the factors that influenced changes in the distribution of large mammals using data collected over 40 years. The research team used habitat distribution data for Asiatic black bears and wild boars from 1978, 2003, and 2014, as well as habitat data for Asiatic black bears, monkeys, and brown bears from 2017 for analysis.
Baek stated that "these animals were said to live in the mountains 40 years ago, but now they are easily found in human-inhabited areas." In fact, the distribution of large mammals in Japan has rapidly expanded over the last 40 years. During this period, sika deer showed an increase in habitat of 2.6 times, wild boars by 1.9 times, Asiatic black bears by 2.0 times, goats by 2.1 times, Japanese macaques by 2.1 times, and brown bears by 1.9 times.
Sika deer are now increasing their habitat by 174.9 square kilometers annually, and their distribution has expanded to the point that there is no area where they do not live. Wild boars have seen their habitat distribution expand in western Japan, and brown bears, although expanding their habitat comparatively slowly at an average of 35.2 square kilometers per year, are now reported to inhabit 80% of Hokkaido.
To pinpoint the reasons behind the significant increase in mammal habitats, the research team divided Japan into small areas of 5 km wide and 5 km deep. They then examined how factors altering wildlife habitat, such as land use, terrain, snowfall, human activities (night lighting), abandoned farmland, and propagule pressure affected the situation.
These factors have indeed been shown to influence the recent expansion of large mammal habitats.
From 1978 to 2003, the deer, wild boars, Asiatic black bears, and goats in Japan tended to expand their habitats into areas with lower human activity (night lighting) and more abandoned farmland in Honshu, Kyushu, and Shikoku. In contrast, brown bears showed an opposing pattern, trying to expand into areas with more cultivated land.
However, as we entered the 2000s, large mammals have increasingly tended to expand their distribution into areas with more farmland. They also showed a tendency to expand their habitats into areas with less snowfall and closer to places formerly inhabited by humans.
Baek is identifying the rapid expansion of wildlife habitats as stemming from population decline and global warming. Japan is facing serious issues with low birth rates and aging populations, similar to Korea, and as the rural population decreases, the amount of abandoned farmland continues to rise. The analysis suggests that as large mammals expand into these abandoned rural areas, contact and conflict with humans increase. A trend was also observed where habitats expanded into higher latitude regions and high-altitude areas that have seen less snowfall due to the effects of global warming.
Baek expresses a desire to emphasize coexistence rather than conflict between humans and animals. He mentioned, "As the density of large wild animals increases, the areas of contact with humans expand, leading to more conflicts and increased risks of zoonotic diseases," adding, "To cope with changes such as global warming and population decline, appropriate distancing and systematic management between humans and large mammals are necessary."
This study is a very rare investigation that uses long-term recorded data over 40 years to address the causes of the emerging issues of wildlife encounters in Japan, garnering the attention of the Japanese media. It also attracts interest that a young Korean scientist is leading wildlife research in Japan.
Baek graduated from the Department of Biology at Jeju National University, moved to Japan, and received his master's and doctor's degrees from Tokyo University of Agriculture and Technology. He has a keen interest in bear research and has been accumulating relevant data on bear habitats and large mammals, continuing his research in Japan. On the day of the interview, he mentioned that he was "on his way back from a field survey."
- It seems that the Japanese media is also very interested in this research.
"Recently, bears and deer have become frequent social issues in Japanese society. News reports have emerged about bears coming down from the mountains and injuring the elderly, and problems like population decline due to aging and global warming seem to be topics of interest in Japanese society."
- What prompted you to study wildlife in Japan?
"Originally, I was conducting research with GPS (Global Positioning System) trackers on Asiatic black bears to monitor their activity and behavior. The Asiatic black bears included in this study are the same species as those in Korea. They are distributed over a wide area from West Asia to Siberia, but most are extinct. In contrast, Japan has a relatively abundant population, capturing thousands of Asiatic black bears each year. I feel that the extensive research available here will allow me to contribute significantly to the preservation of Korean black bears in the future."
- Are the habitats of Korea and Japan very different?
"In both Korea and Japan, urbanization and aging are proceeding similarly. However, Korea has a higher road density, which has resulted in significant habitat fragmentation, making it more difficult for large mammals to thrive. In Japan, large mammals significantly reduced in number due to hunting and slash-and-burn agriculture from the 18th to 19th centuries. However, recently, as rural populations have declined, homes have disappeared, and farming and hunting activities have decreased, the areas preferred by animals have expanded. Compared to Korea, Japan has a slightly better habitat environment."
- It seems that the habitats of large mammals have changed over the past 40 years.
"Although there are differences by timing and species, until about 20 years ago, wild animals avoided areas with high human activity and roamed in areas with less cultivated land. However, in the recent 20 years, wild animals have started to expand their activity ranges into areas with more cultivated land. While these are still cultivated lands, they also have many areas of abandoned farmland. A phenomenon of expanding habitats into areas with less snowfall has also been confirmed."
- Recently in Japan, there are frequent reports such as 'bears have eaten people' and 'monkeys have attacked people.' What animals are causing trouble?
"Primarily deer, wild boars, and bears. In 2023, bear-related incidents have been quite prevalent. However, the main issue is deer, as they are causing significant crop damage. This species, originally found in Korea, is known as sika deer. While the roe deer carefully selects its food, sika deer consume all the fruits and crops around them. Their feeding habits lead to the degradation of forest vegetation, consuming trees and plants at the foot of the mountain, even causing landslides and affecting the breeding of birds and insects."
- The Asiatic black bear is a protected species in Korea, but it seems to be treated as a nuisance in Japan.
"Surprisingly, many people are unaware that Asiatic black bears live in Japan. Even at international conferences, there are scholars who do not know that Asiatic black bears exist in Japan. In fact, only brown bears live in Hokkaido, while Asiatic black bears primarily inhabit areas further south. Unlike in Korea or other habitats, Asiatic black bears are common in Japan. There are many cases where people have been killed or injured due to their attacks. With the recent increase in incidents, the trend has been to relax regulations on capturing bears. Currently, around 3,000 to 5,000 are captured annually."
- Is it because there are no predators that control their population?
"That seems to be a prevalent perspective. Japan once had wolves, which are the ultimate predators. After this single species that could pressure the deer disappeared, only Asiatic black bears and brown bears remain as top predators in Japan. However, Asiatic black bears primarily feed on plants, making them ineffective as a pressure mechanism."
- Between global warming and population decline, which factor has a greater influence on the expansion of wildlife habitats?
"It's difficult to say which one comes first. Just like humans, animals prefer places that are more hospitable. In that process, they are coming closer to humans. It is clear that humans have had a significant impact on limiting animal activities. If population decline continues, animal activity spaces will expand further. If warming continues, areas at higher altitudes or colder regions will see less snowfall, allowing grasses and trees to grow better and facilitating movement."
- If the habitats of large mammals continue to increase, will collisions become inevitable?
"In Japan, the approach is currently to conserve wildlife while reducing problems. The primary actions include regulating populations, providing compensation when issues arise, and ultimately managing habitats to prevent problems from occurring. They are currently considering the concept of zoning, where areas inhabited by wildlife, human settlements, and buffer zones in between are established. In the buffer zones, wildlife will only be captured when they cause problems, while strict controls will be in place in human-inhabited areas."
- Why is it necessary to maintain a distance from wildlife?
"As contact with wildlife increases, there is potential for infectious diseases like COVID-19 to spread. I understand that in the U.S., chronic wasting disease (CWD), which is a prion disease often referred to as deer mad cow disease, is currently becoming a serious issue. When wildlife and humans live in close environments, the risk of zoonotic diseases spreading increases. It is essential for coexistence. If conflicts with animals continue as they are, it is undesirable for negative perceptions to spread that they should be eradicated."
- Should we not be worried in Korea?
While the situation is different, much research like this is needed. Korea is still placing more emphasis on wildlife conservation. However, as wildlife gradually expands their ranges and recovers habitats, I believe similar situations will arise. Korea is also seeing population decline in rural areas. As the number of people living in rural areas decreases and human activities diminish, animals will find it easier to come back.
- 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 currently experimenting with zoning. It's necessary to verify whether these efforts are effective. Our research does not aim to negatively assess these changes. The goal is to seek coexistence with large mammals. When conflicts arise between humans and animals, negative perceptions can grow, leading to the notion that animals, which have returned to nature with great difficulty, need to be eliminated again. Understanding the mechanisms and ecology of how large mammals' habitats are expanding and managing them appropriately is the core of our research for coexistence."
References
Communications Earth & Environment (2025), DOI: https://doi.org/10.1038/s43247-025-02261-w