KYOTO--Reflecting the Japanese traditional aesthetics of “wabi-sabi” (transience and imperfection), moss-covered gardens have long mesmerized visitors from home and abroad.

But there has been increasingly less moss in Kyoto to marvel at in recent years due to climate change.

The prefectural government and temples have started conducting surveys and research to conserve the “important historical landscapes representing Kyoto.”

RISING TEMPERATURES

The ancient capital is home to many famous temples with moss gardens, including Saihoji--or “Kokedera” (moss temple)--Gioji and Tofukuji, while Katsura Imperial Villa is also known for its Japanese garden.

Half of the Japanese gardens the central government has designated as historical sites or special historical sites are in Kyoto Prefecture.

There are about 1,800 moss species in Japan, according to the prefectural government's natural environment conservation division.

Of these, 552 species, or more than 30 percent, inhabit the prefecture. Many of them are rare and included in the Environment Ministry’s Red Data Book of endangered species.

While Japanese gardens provide an important growing environment for moss, the plant symbolizes biodiversity together with Kyoto culture.

But Yoshitaka Oishi, a Fukui Prefectural University professor specializing in moss biology, warns that the lush greenery of moss, which is at the core of the wabi-sabi aesthetics of Japanese gardens in Kyoto, will be lost in 20 to 30 years’ time if no preventative measures are taken.

One major reason lies in long-term temperature increases.

The average annual temperature in Kyoto has risen by about 2 degrees over the past 100 years, according to the Japan Meteorological Agency.

When Oishi surveyed 17 Buddhist temples and Shinto shrines across the city in fiscal 2012, he found a member of the juniper haircap moss, which is susceptible to desiccation, had withered or suffered other degradation in gardens in urban areas, where the temperature is higher and the humidity is lower because of the urban heat-island phenomenon.

Oishi also conducted a joint study with Shinshu University involving an open-roof greenhouse established in the Central Japan Alps.

When the inside temperature was raised by about 0.5 degree compared to the outside air temperature, the moss-covered area decreased by about 30 percent in the six years from 2010.

The plants died because of the rising temperature and the accompanying decrease in humidity.

The survey was conducted at the tree line about 2,600 meters above sea level.

But Oishi said he assumes that similar influences can be seen in moss growing at sea level.

Less fog also poses a threat to moss.

The plant can “take a breather” with fog in the early fall after enduring the heat of summer, Oishi said.

Located in a basin surrounded by mountains, Kyoto has favorable geographical conditions to generate fog.

But according to the JMA, the number of days with fog per year in the city has decreased after peaking at 125 in 1934.

There have been no foggy days for many years since the 1980s, while fog was observed only for three days after the turn of the 21st century.

It is believed the urban heat-island phenomenon has mainly contributed to the decrease because it makes it difficult for the temperature to drop in the morning and at night.

‘CANARY IN THE COAL MINE’

An increasing frequency of sudden downpours are adding insult to injury.

Unlike drizzling rain, downpours wash away moss along with the soils on which they grow.

“Recent environmental changes have been terrible to moss. It has been a rough-and-tumble ride (for the plant),” Oishi sighed.

Moss has a simple structure with no roots or stems.

But that is all the more reason they are susceptible to environmental changes.

“They are like the proverbial ‘canary in the coal mine’ in the plant kingdom, which quickly detects danger,” he added.

DEGREE OF DETERIORATION

The Kyoto prefectural government has embarked on a two-year full-scale study beginning in April 2022.

Aimed at conserving moss gardens, Oishi heads the Koke Platform project.

The project team is tasked with examining changes in moss vegetation at 32 locations year-round to comprehensively assess the influences.

The temperature and humidity at each location are measured once every three hours and the moss distribution in each garden is recorded.

Moss is exposed to light of a special wavelength to evaluate its “degree of deterioration.”

The team will also examine long-term changes based on photos published in past guidebooks, as well as documents and other publications.

A temporary tally for fiscal 2022 showed a decrease in moss vegetation.

The average temperature of the survey points set up at temples and shrines in urban areas is higher than that of suburban areas year-round, with a maximum difference of 4.4 degrees.

Moss disappeared or decreased in vegetation in some of the gardens.

“There is no doubt that moss gardens have deteriorated because of the heat-island phenomenon,” Oishi said.

FOR FUTURE GENERATIONS

Maintaining moss gardens relies heavily on the experience and knowledge of gardeners.

But the prefectural government will consider compiling a conservation manual tailored to different moss species and the environment of each garden, making use of expertise gained from the survey.

Temples have also started working to conserve their moss gardens.

Saihoji is set to launch a project by the end of March 2024 to reconstruct a waterway that previously ran through the temple grounds.

While the aim is to regain a historic landscape, the waterway is also expected to keep the humidity at a certain level after it has dropped due to rising temperatures.

“We want to pass down the moss garden to future generations,” a representative said.

Shigeyoshi Takemura, 51, a gardener at Ueyakato Landscape Co. in Kyoto, has been maintaining the gardens at Nanzenji temple for about 20 years.

With irrigation water from the Lake Biwa Canal running through the temple grounds, located at the foot of the Higashiyama mountains, he feels the effects of the heat-island phenomenon are relatively milder compared to central Kyoto.

“But since moss senses changes in the environment far more acutely than humans, it could be too late when we humans notice there is something wrong with it,” the gardener said. “I hope their scientific analysis will show how environmental changes affect the moss so that it can help maintain the beautiful moss garden.”