Aso, Suntory’s First Natural Water Sanctuary Site

Do you know what kind of forests help sustain rich groundwater? The first thing to take a look at is the soil. In a “healthy” forest, the soil is soft and spongy, soaking up all the rain that falls and allowing it to seep down underground. What cultivates this soft soil? The many living things that call the forest their home. Trees drop dead leaves and branches, and as these pile up on the forest floor, the microorganisms, earthworms, and other creatures that live in the soil break them down and till the soil, making it soft. As good, nutrient-rich soil is created through this process, wild plants and shrubs begin to grow in it, covering the ground. Next, the bugs that eat these plants arrive, along with the small birds and animals that feed on those bugs. They in turn attract the foxes, martens, hawks, eagles, and other large creatures that eat them. This is how a thriving ecosystem develops. And the more biodiverse a forest is, the softer its soil and the better its ability to cultivate and restore water resources. A “healthy” forest is one where all kinds of living things can easily make their homes.

The soil in Suntory Natural Water Sanctuary Aso is spongy and soft to the touch.

We began our Suntory Natural Water Sanctuary Initiative in 2003, here in Aso. At first, we were mostly feeling things out as we went, as it wasn’t yet clear what kinds of interventions would help to replenish groundwater. However, we went on to ask various researchers to collaborate with us, launching an ongoing process of trial and error. Thanks to this, we can finally say with confidence that our interventions are based on science. We can summarize our research findings in the following 2 keys to replenishing groundwater. The first is that creating biodiverse forests is the most important thing if you want to cultivate a healthy soil. The second is selective thinning of overly dense plantations and other forests to control evapotranspiration―water loss from soil and plants―to the appropriate level. This means that we’re not simply thinking about planting flowers because we like them, or cutting down trees because we want to create open spaces where everyone can get together. Instead, we are making decisions on a scientific basis and using survey data, developing a forest management approach that simultaneously replenishes water resources and enhances biodiversity.

In the plantation on the left, where Hinoki cypresses are densely packed, thinning work is carried out to allow sunlight to reach the forest floor. The brightened forest on the right allows living things to thrive, which softens the soil, leading to an increased capacity to replenish groundwater.

From Forests to Rice Paddies: Replenishing Water Throughout the Watershed Area

Another unique approach to replenishing groundwater in Aso is “winter-flooded paddies.” This involves flooding rice paddies during the winter fallow season and allowing the water to seep into the ground. In collaboration with local farmers, we have been carrying out this initiative in the Mashiki area, downstream of our Natural Water Sanctuary Aso, since 2010.
Water that seeps into the soil in a forest filters deep underground. Some of it then emerges as springs, feeding rivers that eventually flow into the sea. Water that surfaces in and around the forests is directed into the winter-flooded paddies, where it seeps back underground. In other words, we are replenishing water resources twice over through the forests and the rice paddies. The reason we are making all this effort is because Kumamoto Prefecture is an area with plentiful groundwater stock, known as the “Land of Water.” Kumamoto City is the only area in Japan with a population of 700,000 that supplies 100% of its tap water from groundwater. As a member of this local community, Suntory conducts surveys of the flow of groundwater across the region and advances initiatives to replenish groundwater—not only for our own plants but for the entire watershed. The Natural Water Sanctuary Aso covers a total area of approximately 420 hectares (around 600 soccer fields), while the winter-flooded paddies cover approximately 13 hectares (around 19 soccer fields).

Working Toward Water Sustainability Is Working Toward Biodiversity

We originally began our winter-flooded paddies initiative to replenish groundwater. However, we found that keeping rice paddies and waterways filled with water during the winter brought various wildlife back to the area. Insects and frogs gathered at the water’s edge, and the creatures that feed on them turned up too. In this way, the winter-flooded paddies have gradually developed into thriving ecosystems, and the project has become an initiative to restore biodiversity, too.
Experts are currently carrying out ongoing surveys of the wildlife there. So far, they have identified a variety of species. The area is steadily turning into a flourishing waterside environment. With local elementary school students also helping with our surveys, the initiative is developing into a community-wide effort to look after our environment. The journey this project has taken us on has even helped us find new opportunities to work to protect the future of our water and fellow living things.

(Read Part II to find out more.)

For Part II, please see Sustaining Water and Wildlife for the Future: Suntory’s Nature Positive Initiatives at Our Natural Water Sanctuary Aso (Part II).