Planting trees to protect farmland from wind is often seen as a simple way to support biodiversity. However, a new study by Japanese scientists shows that in wetland agricultural landscapes, such measures can create unexpected winners and losers among bird populations.
The study, published in the Journal of Environmental Management, was conducted by experts from Hiroshima University led by Masumi Hisano. They examined the impact of tree shelterbelts on birds near Lake Kahokugata in central Japan—a key stopover on the East Asian-Australasian Flyway.
Researchers conducted bird surveys in February-March 2021 and June 2023 using point-count observations. The results revealed a clear ecological trade-off: tree belts supported species associated with shrubs and forest edges but significantly reduced the abundance and diversity of birds from open grasslands and wetlands.
The decline in grassland birds was particularly striking, with their abundance near shelterbelts more than 70% lower than in open areas roughly one kilometer away. "We found that the abundance of grassland birds was more than 70 percent lower at sites near shelterbelts compared to open sites," noted Hisano.
Researchers compare these belts to "ecological walls": they create new habitats for some species while reducing suitable space for those that nest and feed in the open, potentially increasing the risk of predation.
Many programs encourage planting trees and hedges to boost biodiversity, relying on data from Europe and North America. In Asian rice-growing landscapes, where flooded fields serve as a substitute for natural wetlands, the effect appears to be different.
Hisano emphasizes the importance of thoughtful tree placement: "Biodiversity management of farmland must balance structural complexity with the needs of open-habitat species." Future research aims to investigate how belt width, height, and composition impact different territories across various seasons.
Can the same conservation measure help some species while simultaneously harming others?
The team hopes their findings will help develop more precise agro-ecological policies that combine open and wooded landscape elements to preserve diverse bird communities in a changing world.
