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IDEAS

Tiny urban woodlands, big biodiversity

Miyawaki forests mitigate the effects of climate change and offer a host of other benefits, too.

An aerial view of the first Miyawaki forest in the Northeast United States, planted in September in Danehy Park, a former landfill in North Cambridge.SUGi Danehy Park by Dino Kužnik

US cities lose an average of 175,000 acres of tree cover — roughly 36 million trees — per year. That’s one reason Boston Mayor Michelle Wu recently introduced an Urban Forest Plan that aims to grow the city’s tree canopy. Globally, both tropical and colder-climate forests lose millions of hectares to climate change-induced wildfire, logging, and other human activity. This at a time when global carbon emissions are higher than ever.

Forests capture carbon effectively and cheaply, which makes them indispensable in the battle to halt or reverse humans’ destructive influence on the planet.

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One way to mitigate deforestation and climate change involves a decades-old approach that harnesses a variety of native plant species and invites the stewardship of diverse communities: the Miyawaki forest.

In the 1970s, Japanese botanist Akira Miyawaki developed the idea of planting small forests densely packed with native plants. These “pocket forests” can be as tiny as 1,000 square feet, making them viable in urban areas. (The world’s biggest Miyawaki forest, in Lahore, Pakistan, is over 500,000 square feet — more than 11 acres.) The size is far less important than the selection of native plants that make it up.

Miyawaki specialized in phytosociology, the study of plant interactions. (The idea that plants have a social life, for lack of a better term, has gained popularity in recent years.) He learned that the ultra-dense planting of different native species promotes symbiosis as well as competition for sunlight and other resources. These conditions prompt Miyawaki forests to grow roughly 10 times faster than conventional ones.

Volunteers planted 32 native species of plants on 4,300 square feet of land at Danehy Park in North Cambridge.SUGi Danehy Park by Dino Kužnik

Miyawaki’s studies took him to Japan’s ancient sacred shrine forests in the hope of better understanding the interconnectedness of healthy forests. These shrine forests, called chinju-no-mori, contain layers of history. Trees occupy a foundational place in Shintoism, the belief that everything, animate or not, has a spirit or soul; Shinto lore holds that a god once came down from the sky and inhabited a pine tree on top of a mountain.

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Based on his studies, Miyawaki identified four basic plant types whose coexistence promotes and sustains the forests: ground herbs, shrubs, secondary tree species, and primary, canopy-forming trees. Miyawaki forests contain up to 100 native species from each of these four categories.

And the diminutive forests offer more than just environmental benefits. They serve as outdoor classrooms for researchers, students, and residents, who can study real-time changes in the plants, soil, air, and pollinator populations. Just as important, they give residents who want to do more than stew in eco-anxiety something meaningful to do — the forests need regular watering and monitoring for the first few years.

They also boost environmental civism — civics that bolsters the entire ecosystem. Volunteers who plant or tend Miyawaki forests report not only increased physiological health but a deeper sense of belonging, as they, together with others, make a commitment to the forest and the community.

More than 3,000 Miyawaki forests exist around the world, primarily in Asia and Europe. The trend is beginning to take hold here in the United States. In 2021, the organizations Biodiversity for a Livable Climate and SUGi teamed up to plant the first Miyawaki forest in the Northeast in Cambridge’s Danehy Park, a former landfill. A 4,300-square-foot circle, the forest contains 1,400 trees belonging to 32 native species. Despite last summer’s drought, the forest is thriving: 98 percent of the trees planted are still alive, and many have doubled in size. The forest has already become home to birds, butterflies, bees, dragonflies, and many types of fungi.

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In November, I participated in planting the Northeast’s second Miyawaki forest, in Cambridge’s Greene-Rose Heritage Park. Before the planting, Biodiversity for a Livable Climate conducted soil tests at the site, added necessary nutrients to the dirt, and tilled and aerated the 1,400-square-foot rectangular plot. Working with the City of Cambridge, they sourced 900 seedlings, representing 53 different native species of trees and shrubs, including a variety of oaks (red, pin, chestnut, swamp white, and bur), silver and red maples, elderberry, highbush and lowbush blueberry, and sweet birch, hazelnut, black gum, and tulip trees. Volunteers dug holes and planted seedlings after soaking them in tubs of nutrient-rich “compost tea,” a liquid blend of microbes and nutrients brewed like the beverage.

With dozens of unplanted trees in plastic pots left over, we found spots between the trees we’d just planted, just as one might try to find unclaimed surface area for more candles on an elderly person’s birthday cake. A feeling of celebration hung in the air.

As gratifying as it was to put hundreds of trees in the ground, it was even more gratifying to interact with other volunteers and passersby, some of whom stopped, asked what we were doing, and rolled up their sleeves to join us. Bound by a common interest in helping to restore Earth’s ecosystems, volunteers spanned decades, countries, religions, and experiences. Children helped senior citizens with creaky knees and sore backs plant pines, maples, and dogwoods. Women in hijabs gathered to watch, asking about particular species and their characteristics. One volunteer gave away pieces of his mammoth prickly pear cactus with a brief tutorial about keeping them alive.

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That’s what a Miyawaki forest is about: life. Not just plant or animal life — human life, too.

This story was updated on Dec. 21 to correct the reference to the generally accepted minimum size of a Miyawaki forest.

Joelle Renstrom is a science writer who teaches at Boston University.