A team of researchers studying farmland wetlands on the western coast of central Japan found that shelterbelts, rows of trees planted as windbreaks, do not benefit all birds equally. While they provide habitat for some species, they can also reduce the abundance and diversity of birds that rely on open grassland and wetland environments.

The findings were published in the Journal of Environmental Management.

Tree Planting and Bird Conservation

Many agricultural conservation programs encourage farmers to plant trees and hedgerows to increase biodiversity. These woody landscape features, known as shelterbelts, are generally considered beneficial for wildlife.

However, much of the research supporting their value comes from cropland and grassland systems in Europe and North America. Far less is known about their effects in wet farming landscapes such as rice paddies, which are widespread across Asia and provide important habitat for wildlife that depends on wetlands. These habitats are also declining around the world.

"The central question of our study is, 'Do shelterbelts and other woody linear features benefit all farmland birds equally in agricultural wetland landscapes, or do they create trade-offs by disadvantaging species that depend on open habitats?'" said corresponding author Masumi Hisano, assistant professor at Hiroshima University's Graduate School of Advanced Science and Engineering.

The question is especially important because agricultural wetlands serve two roles. In addition to producing food, they function as substitute wetlands for many bird species, including migratory birds traveling along major flyways. If shelterbelts reduce habitat quality for grassland and wetland birds, conservation efforts intended to increase biodiversity could have unintended consequences.

Bird Surveys Around Lake Kahokugata

To investigate, the researchers focused on farmland surrounding Lake Kahokugata in central Japan. The landscape includes large areas of rice paddies along with lotus fields, cultivated cropland, and pastureland.

The region regularly experiences strong winter winds and storms, making shelterbelts a common feature used to protect agricultural fields from wind damage.

Lake Kahokugata is also a key stopover location along the East Asian-Australasian Flyway. Migratory birds use the area during different seasons, with wintering species spending the colder months there and breeding species occupying the region during summer. Nearly 300 bird species have been recorded in the area.

The team conducted bird surveys in February and March 2021 and again in June 2023, using a point count method to measure bird abundance and diversity.

Shelterbelts Create Winners and Losers

The surveys revealed a clear ecological trade-off.

Shelterbelts supported birds associated with shrubs and habitat edges. At the same time, they substantially reduced both the abundance of grassland birds and the diversity of wetland species that depend on large, open areas.

"We found that the abundance of grassland birds was more than 70 percent lower at sites next to shelterbelts compared with open sites located about one kilometer away," said Hisano.

According to the researchers, the results demonstrate that even relatively narrow rows of trees can significantly influence which bird species are able to occupy a landscape.

"A useful way to think about this is that shelterbelts act like ecological walls," said Hisano.

The researchers explain that while shelterbelts create habitat opportunities for some species, they can reduce usable space for birds that nest and feed in open environments. They may also increase exposure to predators.

"Our study provides clear, quantitative evidence that small-scale landscape features can have large ecological consequences, directly relevant to land-use planning and environmental management," said Hisano.

Why Tree Placement Matters

Rather than framing trees as either beneficial or harmful, the researchers say their results highlight the importance of where and how trees are incorporated into agricultural landscapes.

"Biodiversity-friendly farmland management must balance structural complexity with the ecological needs of open-habitat species, especially in landscapes where wetlands have already been heavily modified by humans," said Hisano.

The team argues that this message is particularly relevant because many agricultural conservation programs encourage tree planting without fully considering how those changes may alter entire bird communities.

Future Research and Conservation Planning

The researchers say future studies should explore how specific shelterbelt characteristics, including width, height, spacing, configuration, and tree species composition, influence wildlife across different regions and seasons.

They also hope to better understand indirect effects, such as how shelterbelts may alter predator activity and habitat connectivity, which could further influence bird populations.

"Ultimately, our goal is to help design evidence-based agri-environmental policies that work in wet-farmed landscapes worldwide. Rather than promoting a single solution, such as planting more trees everywhere, we aim to support landscape-level planning that combines open habitats and woody features in ways that sustain diverse bird communities and the ecosystem functions they provide. By doing so, agricultural wetlands can remain productive for people while continuing to serve as vital habitats for wildlife in a rapidly changing world," said Hisano.

The research team included Masumi Hisano with Hiroshima University, The University of Tokyo, and Kyoto University; Shota Deguchi with Fukui City Museum of Natural History; Wenhuan Xu with University of British Columbia and Simon Fraser University; Xike Xiao with Hiroshima University; Keinosuke Sannoh with Nihonkai Eco Engineering Technologies; Xinli Chen with Zhenjiang A&F University; and Ken Motomura with Nakano City Hall.

The study was supported by Kahokugata Lake Institute and the Japan Society for the Promotion of Science KAKENHI.