New Research Reveals Excessive Tree Planting May Harm Bird Diversity

A recent study has revealed that planting trees around agricultural fields to protect crops from storms can significantly impact bird diversity. Researchers at Hiroshima University in Japan have found that shelterbelts—rows of trees planted around fields—while beneficial to some bird species, cause a sharp decline in populations of birds that prefer open habitats such as wetlands and grasslands. This study was published in the Journal of Environmental Management.

Many agricultural conservation programs worldwide encourage farmers to plant trees along field edges to enhance biodiversity. However, most previous studies have focused on dry farmland regions in Europe and North America. There is little information on how tree planting affects birds in humid, waterlogged agricultural landscapes like the rice paddies common in Asia. According to Masumi Hisano, assistant professor and lead researcher at Hiroshima University, agricultural wetlands not only produce crops but also serve as alternative habitats for migratory birds.

To investigate this, the research team conducted fieldwork around Lake Kahokugata in central Japan, studying rice fields, lotus fields, and pastures. This region experiences strong winter winds, leading to the widespread planting of trees along field boundaries to act as windbreaks. Situated along the East Asian–Australasian Flyway, the area hosts nearly 300 migratory bird species year-round. Scientists carried out bird counts and species identification in February and March 2021 as well as June 2023.

The findings revealed that while shelterbelts benefit birds that dwell near shrubs and forests, they substantially reduce the diversity of species dependent on open grassland and wetland habitats. Grassland bird populations near tree rows declined by more than 70% compared to open areas. Hisano explained that these tree belts act as “ecological barriers” for birds that nest and forage in open spaces, increasing their vulnerability to predators. The researchers emphasized that tree planting itself is not inherently harmful, but careful consideration of location and configuration is critical when managing agricultural landscapes. Rather than indiscriminate tree planting, landscape planning should balance open habitats with tree cover to maintain biodiversity. This research provides vital guidance for designing biodiversity-friendly agricultural policies and securing human-made wetland environments as safe habitats for birds.