Planting tree belts on wet farmland comes with an overlooked trade-off

(Press-News.org) A research team has conducted a study to examine how shelterbelts influence bird species diversity and composition in an agricultural wetland landscape on the western coast of central Japan. They determined that shelterbelts, trees planted to protect the land from wind, in farmlands are not automatically beneficial for bird diversity.

Their research is published in the Journal of Environmental Management on January 15, 2026.

Many agri-environmental policies promote planting trees and hedgerows in farmland to enhance biodiversity. These woody features, called shelterbelts, are widely assumed to be beneficial. However, most of the evidence supporting their benefits comes from croplands and grasslands in Europe and North America. Much less is known about how these shelterbelts affect wet-farmed landscapes, such as rice paddies, that are common across Asia and support wildlife dependent on wetland habitats, which are now declining globally.

“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.

This question is important because agricultural wetlands are not only food-producing systems but also serve as surrogate wetlands for many bird species, including migratory species along major flyways. If these shelterbelts unintentionally reduce habitat suitability for grassland and wetland birds, the conservation actions could undermine the biodiversity they aim to protect.

Small tweaks, big consequences The team focused their study on the fields around Lake Kahokugata in central Japan. The lands there consist of mostly rice paddies, but also lotus fields, cultivated croplands, and pastures. The Lake Kahokugata area experiences strong winds and storms during the winter. Shelterbelts are planted along agricultural fields there to protect croplands from wind damage.

This area is an important stopover site for migratory birds along the East Asian-Australasian Flyway. Wintering birds spend the cold months there and breeding species use the area during the summer. Almost 300 different bird species have been recorded in the area. The team conducted their bird surveys in February and March 2021 and June 2023. They used a point-count method to collect the bird data.

The bird surveys showed that in wet-farmed landscapes, shelterbelts create a clear trade-off. They support bush- and edge-associated birds, but at the same time they strongly reduce the abundance of grassland species and diversity of wetland species that require large, open spaces.

“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 kilometre away,” said Hisano. This shows that even narrow, linear tree features can dramatically alter what birds can live in a landscape.

“A useful way to think about this is that shelterbelts act like ecological walls,” said Hisano. The shelterbelts create habitat for some species, but for others, particularly birds that nest and forage in open ground, they shrink the usable landscape and 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.

Spatial design guides outcomes The team explains that rather than asking whether woody vegetation is “good” or “bad,” their study shows that the spatial design and placement of trees matter. “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 considers their management-focused message to be crucial because many current agri-environmental schemes promote tree planting without considering how it reshapes entire bird communities.

Looking ahead, the team notes that future research needs to examine how different shelterbelt designs, such as width, height, spacing, and configuration, and tree species composition and diversity, affect wildlife across seasons and regions. They also want to better understand how birds respond indirectly through changes in predator activity and habitat connectivity.

“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 includes 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 research was supported by Kahokugata Lake Institute and the Japan Society for the Promotion of Science KAKENHI.

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About Hiroshima University

Since its foundation in 1949, Hiroshima University has striven to become one of the most prominent and comprehensive universities in Japan for the promotion and development of scholarship and education. Consisting of 12 schools for undergraduate level and 5 graduate schools, ranging from natural sciences to humanities and social sciences, the university has grown into one of the most distinguished comprehensive research universities in Japan. English website: https://www.hiroshima-u.ac.jp/en

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