Saving forests to protect coastal ecosystems: Japan sets historic example

KESENNUMA CITY, Japan — Forests cloak steep slopes descending from the tree-covered peak of Oshima Island, while oyster farms dot the deep blue waters of the strait below. On a far shore, houses cluster below the wooded slopes of more steep hills. This verdant view makes it easy to fathom how this area sparked a nationwide movement to conserve forests as a way to protect estuary fisheries.

Still, Kesennuma is far from the only place in Japan where people appreciate and cultivate healthy forests to contribute to healthy coastal waters. The island nation — with its more than 30,000 kilometers (nearly 19,000 miles) of coastline, nearly 100major river systems, and two-thirds of its land covered in trees — has long inspired various actors to protect onshore watersheds as a way to preserve water quality in the bays and estuaries they feed into.

The government, for example, designates certain woodlands as “protection forests” based on the ecosystem services they provide. Among the 17 categories of protection forest, “fish forests” specifically highlight the relationship between forests and coastal seas.

Japan’s commercial fishers, too, have played a leading role in raising awareness of watershed importance. Beginning in the late 1980s, fishers in Kesennuma and other locales began planting trees with the goal of safeguarding their marine livelihoods.

Today, Japanese researchers are finding evidence of the benefits forests provide for marine life, confirming the local knowledge fishers have garnered over generations through firsthand experience. In 2021, researchers from Hokkaido University and Kyoto University found that greater watershed forest cover correlates to a higher number of vulnerable fish species in the watershed estuaries studied.

But while it’s tempting to imagine forests as a silver bullet for preserving marine ecosystems, experts point out that the interplay between Japan’s people, forests and seas is complex, with results not necessarily aligning with the simple environmental narratives people construct.

However, Japan’s historical forestry example, and its ongoing research into the terrestrial-oceanic interface, could benefit the rest of the world — especially as intensifying land-use change and worsening climate change-driven storms increase agricultural and industrial pollution and soil erosion that can degrade coastal fisheries.

A national system based on centuries of experience

Japan introduced its protection forest system, which regulates the logging of forests that provide a variety of ecosystem services, more than a century ago, in 1897. Out of the 12 million hectares (30 million acres) currently designated as protection forests, just 0.4% fall into the “fish forest” category. However, other categories such as forests conserving headwaters and those preventing erosion, landslides and floods likely also contribute to healthy coastal ecosystems.

According to Japan’s Fisheries Agency, “fish forests” contribute to healthy coastal seas by controlling runoff and generating nutrients brought to the sea via rivers and streams. Records indicate that Japan has been protecting forests to help safeguard fisheries for 1,000 years, according to a 2020 article by the Research Institution for Humanity and Nature in Kyoto. But those millennial records indicate a more simplistic approach, with “historical fishery forests … meant to provide shade for fish to congregate” rather than as a means of better managing entire watersheds.

The Ohayashi, literally “the wood,” in Kanagawa prefecture’s Manazuru Peninsula is one example of a designated “fish forest” — but one with a surprising history.

“Actually, there wasn’t originally a forest there,” Daisuke Takata, a member of the Manazuru town hall’s tourism promotion team, told Mongabay. “In the early Edo period [1603-1867] it was a field of kaya, the grass used to thatch roofs.”

Then, in 1657, much of Edo (now Tokyo) was destroyed by fire. With the country’s forests already overharvested, the government didn’t have sufficient timber to rebuild the capital. So the local lord was ordered by the central government to grow 150,000 pine trees on Manazuru Peninsula. In the Meiji period (1868-1912), camphor trees were planted in the forest. The thriving woodland was designated a “fish forest” in 1904.

“Since the Edo period, the area where Manazuru’s ‘fish forest’ is now has been known as a place where fish congregate,” explained Masaru Suzuki, head of the Manazuru Tourism Association secretariat, in an interview. “During that period, various domains would plant and maintain trees along the coast.”

Manazuru’s history illustrates the overlapping uses of natural resources by varied members of society, demonstrating the intentional shaping of the natural environment to benefit humans long before Japan’s industrialization and globalization.

Today, dozens of fish species, along with shrimp, abalone and other mollusks, are harvested in the waters around Manazuru. Roughly 10% of the catch is consumed locally, while much of the rest is sent to processing facilities around the country, according to Takata. The shade and nutrients provided by the Ohayashi fish forest, along with the sea’s depth and abundant plankton and seaweed, combine to create an ideal marine habitat.

“Manazuru’s fishing grounds aren’t supported by just the Ohayashi [woodland],” explained Suzuki, who pulled out a map of the peninsula and surrounding area. “Looking at the big picture, there are three rivers that flow [into Sagami Bay], and a current circles around the bay toward the peninsula,” bringing nutrients.

The forest, though originally planted with pine and camphor, also now boasts a native species of chinquapin tree called sudajii (Castanopsis sieboldii), which naturally seeded itself over the years. In the rich soil toward the center of the Ohayashi, the native sudajii is gradually overtaking the earlier planted species, though pine continues thriving on the wood’s rocky edges, according to town surveys.

Manazuru’s municipal policy for preserving the Ohayashi fishery forest states the city’s intention to leave the 350-year-old forest “as untouched as possible, and its landscape should be left for generations to come.”

‘The forest is the sea’s sweetheart’

Despite the long history of the protection forest system, pollution from factories and other industrial uses started to degrade river and coastal fisheries as Japan rapidly industrialized through the early and mid-20th century. Fishers fought back. With their livelihoods on the line, they became some of Japan’s strongest advocates for watershed conservation.

In 1989, fishers in Kesennuma began actively planting trees in a local watershed. The group was led by oyster farmer Shigeatsu Hatakeyama, who coined the phrase mori wa umi no koibito — “the forest is longing for the sea, and the sea is longing for the forest” (or, more literally, “the forest is the sea’s sweetheart”).

Shigeatsu established Mori wa Umi no Koibito, an NGO that today he runs with his son, Makoto Hatakeyama. In an interview with Mongabay, Makoto explained the immediate impetus for tree planting by the fishers in 1989: “Actually, this was a movement to protest the planned construction of a major dam on the [Oh River] that flows into the sea at Kesennuma. Although the fishers didn’t have any concrete [scientific] evidence, they felt from experience that a major development project in the watershed would change the sea life.”

Kesennuma’s fishers had long observed that shellfish thrived after the annual snow melt, as increased nutrients from the forest fed phytoplankton and, by extension, aquatic predators and filter feeders. “They knew intuitively that a development project would be bad for their oysters,” he said.

The decision to plant trees in the Oh River watershed was an act simultaneously rooted in tradition and informed by a growing scientific understanding of watershed ecosystems. The plantings were also calculated to attract attention: Environmental awareness was growing in Japan by the late 1980s, and the human interest story of “fishers planting trees” was covered by national and international media.

Tree planting quickly became popular with fishing cooperatives throughout Japan, including some projects that developed concurrently with, rather than being inspired by, Kesennuma. The mori-umi movement was even written into Japanese school textbooks.

The Oh River dam project was suspended in 1997, and permanently canceled in 2000.

Today, there’s still little scientific evidence of the extent to which annual tree-planting festivals have helped Kesennuma’s estuary. Data the NGO collected up to 2011 was lost in that year’s tsunami, which devastated the city. Makoto guesses it will take decades before new data can reveal any marine health improvements potentially caused by healthy forests.

But even then, proving causation will be difficult. Various other factors, such as local factories opening or closing, can also impact sea life. The forest changes too: The low mountains around Kesennuma are pockmarked with recent clear-cuts, where trees were harvested during a short-lived timber bubble at the beginning of the COVID-19 pandemic.

In Makoto’s view, the major positive impact of the tree-planting movement is psychological: It heightened people’s environmental awareness. Today, those who participated in the first tree-planting festivals 35 years ago are old enough to hold positions of authority, and they also bring their own children to participate in today’s tree-planting festivals. Residents of the village where the festival is held have also launched independent conservation initiatives in their community.

“I think, in the end, it’s about education,” Makoto said. “People are the ones who decide whether a natural environment is good or bad; people are the ones who protect or destroy nature. I think our movement has shown that things can change when you equip people with evidence.”

Science weighs in: Forests protect vulnerable fish species

Finally, in 2021, scientific data was published substantiating the intuitions of Japan’s fishers, making the connection between healthy forests and healthy seas. A studypublished in the journal Conservation Biology found that a greater number of vulnerable fish species found on Japan’s red list were present in estuaries whose watersheds had greater forest cover. The researchers used environmental DNA metabarcoding analysis to accurately determine the number of fish species present in 22 estuaries across Japan.

“The fact that the proportion of forest cover was overall the only significant variable influencing the number of red-list species per site indicates that forests play a more vital role … than originally thought,” wrote the authors.

“Forests are one of the main producers of organically bound iron,” they explained. “Because iron is one of the major limiting factors for primary productivity in coastal systems, forests are thought to play a certain role in enriching estuarine and coastal habitats with iron.”

While the study found that forest cover correlated with a greater number of threatened species, tree cover did not appear to impact overall species richness. Study co-author Akihide Kasai, a professor with Hokkaido University’s Faculty of Fisheries Sciences, told Mongabay that some fish species, such as carp, actually prefer poor-quality water.

“On the other hand, many species on the red list are very sensitive to water quality and can’t live in a place that doesn’t have clean water,” Kasai explained.