Just a 20-minute walk from Hanno Station in Saitama Prefecture is Mount Tenran, a 197-meter peak that looks more like a big hill than a mountain. Nevertheless, it’s a popular destination for day hikes and holds a special place in the community, with a local sake brewery paying tribute to the summit by naming its signature tipple after it.
Mount Tenran is also part of the approximately 1,000 monitoring sites across Japan where fixed-point observations of the status of flora and fauna are conducted. This project is spearheaded by the Environment Ministry and overseen by nature conservation groups and research organizations with the help of thousands of volunteers.
Called Monitoring Sites 1,000, the ambitious initiative, launched in 2003, aims to track the ecosystems of locations deemed important for biodiversity conservation over a period of 100 years. The sites are spread across alpine belts, forests and grasslands, freshwater zones, coastal areas, sandy beaches, coral reefs and small islands.
The survey also includes satoyama, a Japanese term referring to the human-influenced natural environments sitting at the border of "sato," where people live, and "yama," the mountains. Mount Tenran and its neighbor, the 271-meter Mount Tonosu, fall under this satoyama categorization, and that’s why volunteers Akira Oishi and Shinichi Okanobori have taken on inspecting the area’s plants, butterflies, frogs, fireflies and birds, as well as mammals such as deer, wild boar and the Eurasian harvest mouse.
“We’ve been monitoring Mount Tenran since September 2008,” says Oishi, who heads a seven-person team tasked with recording the ecological changes in the mountains and their foothills.
Oishi says one of the things he finds most interesting about the work is seeing how things affect each other. “For example,” he continues, “there was a year when we saw a growth in the number of yamaakagaeru (montane brown frog) after we made rice paddies. Then, their numbers suddenly fell. Why? It turns out the raccoon population is increasing, and they’re eating the frogs, so we had to find ways to get rid of the raccoons.”
Last month, the Environment Ministry and The Nature Conservation Society of Japan (NACS-J) released a report compiling the Monitoring Sites 1,000 project’s findings through March 2022. The report warned that the numbers of butterflies, sparrows and other birds living in satoyama areas are in rapid decline — a threat to biodiversity, which is essential in securing our food supply, clean water and medicines.
In fact, biodiversity also plays an important role in tempering the impact of extreme weather like torrential rainfall, wildfires and droughts, events that we have been seeing more of in recent years due to climate change. And although global warming is not the main threat to nature's variety — that would be land-use change — it is a driver of biodiversity loss.
“Climate change is a big factor, for sure,” says Okanobori, who monitors birds and mammals in and around Tenran and Tonosu. Twice a year, during the breeding and wintering seasons, he would walk a fixed route back and forth three times to count the number and species of birds he saw and heard. Mammals are observed using trail cameras from spring through autumn.
“For some species, global warming has resulted in temperatures that are less than optimal for their survival,” he says. “Meanwhile, a proliferation of deer has seen forest undergrowth eaten up, which is also having an impact.”
The problems aren’t confined to satoyama areas. Butterflies typically found in southern areas of the country are becoming more common up north, along with trees that prefer the warmer climes. The distribution of invasive bird species — such as the Chinese hwamei and the red-billed leiothrix — is on the rise, and reports of coral bleaching are increasing, likely due to elevated seawater temperatures in the summer.
“The idea is to record the changes we observe in the local ecosystem,” says Oishi, who is responsible for monitoring butterflies, “so that necessary steps can be taken.”
The satoyama situation
Oishi and Okanobori are among approximately 5,700 citizen surveyors who, between 2005 and 2022, have been involved in the satoyama survey organized by NACS-J. The satoyama report released on Oct. 1 contains a summary of the results from observations conducted during this 18-year period at 325 monitoring sites nationwide, which the conservation group oversaw.
Some of the statistics were alarming: 33% of butterfly species and 15% of the native bird species in satoyama areas showed steep population declines of 3.5% or more per year. If the trend continues, sparrows and other birds — as well as butterflies such as the Japanese emperor, commonly seen in human-populated areas — may fulfill one of the criteria required for inclusion on the Environment Ministry’s Red List of endangered species, according to the report.
“Birds, butterflies and plant populations are relatively stable in forests, but species in our agricultural and open environments are rapidly declining,” says Taku Fujita, team leader of NACS-J’s biodiversity conservation department.
”The causes aren’t easy to pinpoint,” he adds. “Attributing this solely to global warming would be premature. Still, for example, if you’re taking a walk you may feel the forest is cooler while the area outside is hotter. Well, other living organisms feel the same thing.”
Despite reservations by experts to cite climate change as the sole culprit, the report notes that the average annual temperature in Japan rose steadily between 2008 and 2020, an increase that appears to correlate with a decline in the number of grassland species such as native plants, birds and butterflies. More specific observations find that birds who inhabit zones with a typically narrower temperature range are expected to see a decrease in their numbers, and that the egg-laying period for the brown frog has been brought forward by five to 10 days over the past decade.
“These results align with what is happening in the rest of the world,” Fujita says.
On Tuesday, U.N. Secretary-General Antonio Guterres called for decisive action to restore harmony with nature at the opening of the 16th Conference of the Parties to the U.N. Convention on Biological Diversity, better known as COP16.
“Every year, we see temperatures climbing higher. Every day, we lose more species. Every minute, we dump a garbage truck of plastic waste into our oceans, rivers and lakes," he said. "Make no mistake — this is what an existential crisis looks like.”
According to a WWF Living Planet Report from 2022, wildlife populations — mammals, birds, amphibians, reptiles and fish — have experienced a 69% plunge on average since 1970. Meanwhile, a research article published in PLOS in 2017 that investigated insects over a 27-year span in 63 German conservation areas estimated a more than 75% decline in total flying insect biomass.
While these statistics appear to point to a bleak future in terms of biodiversity, Fujita says “monitoring the changes happening in ecosystems can help us take the appropriate steps.”
For instance, Heike and Genji fireflies communicate with each other through their bioluminescence. Artificial lighting that includes similar wavelengths has intensified in recent years due to a societal shift to LED lighting, interfering with firefly communication and generating light pollution.
This led to the creation of firefly monitoring sites, including one along the Sakatsuki River in the city of Chiba, where a local volunteer group conducts conservation activities and environmental surveys. In 2021, the group joined discussions with the city after observing a dramatic decline in Heike fireflies by a riverside path. The drop came after light fixtures for the overpass and a tunnel on the southern side of the site were upgraded to higher brightness in 2018.
Utilizing data from satoyama surveys, the group requested local officials take measures against light pollution. As a result, construction was carried out in March 2022 to install louvers on some of the light fixtures, while lighting equipment in the tunnel was relocated.
“The goal of Monitoring Sites 1,000 is to capture the changes happening in nature,” says Shun Amemiya, an official at the Environment Ministry’s Biodiversity Center of Japan who is tasked with overseeing the project. “Since we can’t predict when these changes will occur, it’s necessary to have a system in place that provides information once something is detected.
“The purpose is to offer a reference for government departments at the national or local level that are specifically responsible for managing protected areas and eradicating invasive species as part of their conservation efforts.”
Expanding north
While NACS-J handles satoyama surveys, the Japan Wildlife Research Center (JWRC) is responsible for monitoring alpine zones, forests and grasslands, and coral reefs.
Alpine zones are areas that are above the tree line, and are typically populated by alpine dwarf pines. On Hokkaido, this refers to an altitude 1,200 meters above sea level, while on Honshu, the threshold is 2,500 meters.
“Dwarf pines typically grow at lower altitudes, while alpine plants are more common as you go higher,” says Shigeru Niwa, a senior JWRC researcher. “However, the growth of dwarf pines is becoming more expansive, which is also related to global warming.”
For example, surveys of surface-dwelling beetles at four locations on Mount Haku, straddling Ishikawa and Gifu prefectures, found a notable decline in both the number of individual and different species of alpine beetles, while species primarily found at lower elevations, such as kuronagaosamushi, a black ground beetle, were newly identified.
Meanwhile, the growth in deer population is impacting the habitats of various other animals, including bird species like the Japanese bush warbler and the Siberian blue robin, which prefer underbrush. The distribution range of deer has expanded, and they have also been observed in alpine areas in recent years, damaging high-elevation plants.
“In forests and grasslands, the effects of global warming are becoming quite pronounced,” Niwa says. “When measuring tree composition at 48 locations nationwide, we found that in each area, species that prefer warmer conditions are increasing, while those that prefer colder environments are declining.”
Looking at marine environments, in the waters south of Kagoshima Prefecture’s Tanegashima and in coral communities at higher latitudes, researchers have measured sea temperatures at depths of 2 to 8 meters where corals thrive and have been investigating the rate of coral bleaching.
At most of the survey sites, they observed a significant increase in sea temperatures from 2003 to 2022. Additionally, large-scale bleaching events occurred during the summers of 2016 and 2017 due to elevated water temperatures.
“The severity and frequency of widespread coral bleaching events across Japan is increasing,” says Yuko Kitano, Niwa’s colleague and also a senior researcher.
“A significant coral bleaching event occurred in 2022, and another is happening in 2024, indicating a shorter interval between events. As a result, coral recovery is not keeping pace.”
A race against time
Strolling along the forest path on the foothills of Mount Tenran, Oishi and Okanobori point to the plentiful variety of plant and animal life around them — both native and alien.
There are traces of wild boars wallowing by the trail and a bush where the surveyors found pairs of tiny reddish-brown harvest mice. “They’re quite cute,” Okanobori says.
During early summer, Oishi says fireflies can be seen flashing by a stream flowing along the mountain, while the calls of the invasive Chinese hwamei echo between the trees.
This rich natural environment was once on the verge of being lost, however, when the Seibu Railway conglomerate planned a major residential development project in the 1990s.
The plan was eventually scrapped following the burst of Japan’s asset price bubble as well as continued opposition from the nonprofit organization that Oishi is a part of. Now, both the city of Hanno, Seibu and local citizens take part in the maintenance and preservation of the area.
One project they worked on together was the creation of rice paddies by Mount Tenran’s trail where both volunteers and children can experience planting and harvesting.
“Human hands are useful in conserving nature,” Okanobori says. “By maintaining rice paddies in satoyama, for example, a unique ecosystem emerges.”
Satoyama surveys between 2018 to 2022 showed that most monitoring sites have abandoned agricultural areas and have experienced a rapid expansion of oak wilt disease over the past five years, a trend that’s also evident in the forests on Mount Tenran.
“Despite active conservation efforts by citizens at survey sites across the country and the yearly increase in their achievements, the degradation of satoyama and the loss of biodiversity have not ceased,” NACS-J wrote in its report. “That suggests that the loss of biodiversity in satoyama across Japan is even more serious.”
In order to raise awareness and carry on this century-long project, the continued support of surveyors such as Oishi and Okanobori is crucial. However, the project faces serious challenges according to NACS-J, due to the aging of its participants and a shortage of successors.
For now, though, grassroots efforts continue across Japan in an effort to maintain the delicate balance between nature and civilization.
“Local schools and kindergartens often arrange field trips to Mount Tenran so kids can enjoy and learn from being outdoors,” Oishi says. “That’s part of why we do this — so the next generation can appreciate the nature we have and show interest in its conservation.”
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