Planting trees along farmland to protect crops from wind can actually drive away many bird species, a new study from Japan reveals. Researchers found that shelterbelts, rows of trees planted as windbreaks, caused grassland bird numbers to drop by more than 70 percent in nearby fields. The finding upends the common assumption that adding trees to agricultural landscapes is always good for wildlife.
Shelterbelts Help Some Birds, Hurt Others
The study focused on farmland wetlands around Lake Kahokugata on the western coast of central Japan. This area is a key stopover for migratory birds traveling along the East Asian-Australasian Flyway. The landscape is dominated by rice paddies, lotus fields, cropland, and pasture. Strong winter winds and storms make shelterbelts a common sight, planted to shield crops from damage.
Researchers from Hiroshima University surveyed bird populations across these fields. They found that while shelterbelts provided habitat for some bird species, they sharply reduced the abundance and diversity of birds that depend on open grassland and wetland environments. Grassland bird abundance dropped by more than 70 percent near the tree rows. The study was published in the Journal of Environmental Management.
Why Local Farmers and Conservationists Should Care
Agricultural wetlands like those around Lake Kahokugata serve a dual purpose. They produce food, and they act as substitute wetlands for many bird species, including migratory birds. These habitats are declining worldwide. Many conservation programs encourage farmers to plant trees and hedgerows to boost biodiversity. But most of the research supporting that practice comes from croplands and grasslands in Europe and North America, not from wet farming landscapes like Asian rice paddies.
Masumi Hisano, assistant professor at Hiroshima University and lead author of the study, said the central question was whether shelterbelts benefit all farmland birds equally in agricultural wetland landscapes, or whether they create trade-offs by disadvantaging species that depend on open habitats. The results suggest that well-intentioned conservation measures can create unexpected winners and losers.
A More Complicated Picture for Conservation
The study does not argue against planting trees. It shows that the effects of shelterbelts depend on the landscape and the species involved. In agricultural wetlands, where open habitat birds are already under pressure, adding trees can make things worse. Conservation programs that promote tree planting as a universal good may need to reconsider, especially in regions where rice paddies and other wet farmland provide critical habitat for birds that need wide open spaces.
