Japan's rice-farming areas face two broad trends: field abandonment and farm modernization. Both impact the environment as well as the economy.

"When rice fields disappear, species such as tadpoles and dragonflies that live in them decrease. Paddies also store water and help prevent floods. We need to think more about the multiple functions of farmland," said Nobuhiro Suzuki, an agriculture economist at the University of Tokyo.

But paddies and their elaborate irrigation networks provide a home — or feeding ground — not just for tadpoles and dragonflies, but for thousands of species including salamanders, fish, water bugs, snakes, cranes, egrets and hawks.

Today, the Environment Ministry estimates that half of Japan's endangered plants and animals live in these rapidly changing rural areas. To get a better picture of what happens to the environment when farmers try to grow more rice at lower costs, The Japan Times talked to Shori Yamamoto, who leads the Research Project for Biodiversity in Paddy Landscapes at the National Institute for Agro-Environmental Sciences in Tsukuba, Ibaraki Prefecture.

How have past attempts to improve efficiency on Japanese rice farms, such as paddy modernization and consolidation projects, affected biodiversity?

Many recent scientific studies show that these projects do affect biodiversity. For example, pesticide, herbicide and chemical fertilizer use have damaged wildlife populations in and out of fields.

Also, structural improvements, such as changing fields from amorphous to square, and from year-round wetlands to summer-only wetlands, have caused many wildlife habitats to disappear.

Other impacts are less universal. For example, squaring-up of paddies sometimes causes soil runoff, but in other cases robustly constructed levees protect paddy areas from floods or soil erosion.

Is there a link between farm size and rice farmers' agro-chemical use?

I don't think so. Agro-chemical use depends on the farmer's motivations. Usually, chemicals are used for commercial production regardless of farm size. But oftentimes farmers don't use chemicals on the rice they grow for their own families. Recently, more farmers are also trying out environmentally friendly methods as a way to meet consumer demand for safe foods and get a higher price for their rice.

Some people argue that smaller farms with high labor input have fewer negative impacts on biodiversity. But others say that by using low- or no-till methods, and/or cover crops such as winter-grown vetch that's tilled in to the paddy as "green manure" come spring, farmers can reduce costs and environmental impact at the same time. Is there any scientific evidence to back up either of these viewpoints?

I think the former opinion is correct in some ways, because regions with small farms often have highly heterogeneous landscapes. Paddies that are terraced or at the bottom of narrow valleys are often bordered by forests or grassy areas. Biodiversity in traditional Japanese rural areas depends on these mixed landscapes long maintained with high labor input from farmers. But over the past 50 years, even on small farms, chemical use has risen and fields have been modernized.

On the other hand, we have little evidence about the positive effect of cover crops and low- or no-till methods on biodiversity. We're currently doing a project with the Environment Ministry to evaluate the effect of "environmentally friendly agriculture" on biodiversity. We've found that there is a positive effect on the populations of species that naturally control pests, but we also found that impacts differ according to field location, climate and landscape heterogeneity.

Is there any scientific consensus about the relationship between intensive farming and environmental impact on rice farms?

The current consensus is that overly intensive agriculture has a negative impact on biodiversity. On the other hand, excessively low-intensity farming has a negative impact on production.

If farmers want to use non-intensive methods without reducing productivity, then they need higher labor inputs — similar to traditional practices. But in the countryside in Japan, the number of farmers has been decreasing and the average age of those remaining has been going up. This means that labor-intensive methods are difficult to sustain.

We at NIAES are trying to help develop a truly sustainable agriculture that balances environmental conservation and productivity.