tree planting and bird populations: Does planting more trees on farmland actually hurt bird populations? Here’s what a new study reveals about hidden risks of tree planting
A study of agricultural wetlands in Japan found that rows of trees planted as windbreaks, or shelterbelts, can create winners and losers among bird populations. While some birds may benefit from these woodlands, the numbers of those dependent on open grasslands and wetlands may decline.
The findings, published in the Journal of Environmental Management, suggest that conservation strategies may need to consider the needs of different species before altering the landscape, according to a report by Science Daily.
Can planting trees harm some bird species?
For years, conservation programs have encouraged farmers to add trees and hedges because these features are generally thought to be good for wildlife.
These wooded landscape features, known as shelter belts, can provide shelter, nesting sites, and habitat for certain species. But researchers say their effects may depend largely on the environment in which they are introduced.
Most previous research supporting shelter belts has focused on grasslands and croplands in Europe and North America. Less attention has been paid to wet agricultural areas, such as rice paddies in Asia, which serve as important habitat for many birds. These wetlands are already declining worldwide, making it important to understand how changes in agricultural lands affect wildlife.
Masumi Hisano, assistant professor at the Institute of Advanced Science and Engineering at Hiroshima University and corresponding author of the study, explained the basic question behind the research.
“The central question of our study is, ‘Do shelter arches and other woody linear features benefit all farmland birds equally in agricultural wetland landscapes, or do they create trade-offs that disadvantage species that depend on open habitats?'”
What happened around Lake Kahokugata?
To investigate the effects of shelter belts, researchers examined farmland around Lake Kahokugata in central Japan. There are large rice fields, lotus farms, cultivated fields and pastures in the region. Since the region experiences strong winter winds and storms, protection belts are often erected to protect agricultural areas.
Its location is also important for birds because it lies on the East Asia-Australia Flyway, an important route used by migratory species.
Birds visit the area in different seasons; Some stay in winter, some come during breeding seasons. Nearly 300 bird species have been recorded around the lake.
Researchers conducted bird surveys in February and March 2021 and again in June 2023. Using point counts, they measured both the number of birds and the diversity of species living in different areas.
Which birds benefited from shelter belts?
The results showed a clear distinction. Shelter belts helped birds that preferred shrubs and habitat edges. These areas have created new opportunities for species that can live comfortably near trees.
But the same rows of trees had negative effects on birds that need large, open environments. Meadow birds were especially affected. The researchers found that abundance near shelter belts was less than 70 percent compared to open areas about a kilometer away.
Hisano described this effect as follows: “A useful way to think of this is that shelter belts act like ecological walls.”
Even narrow rows of trees can change the way animals use the landscape, the researchers explained. For birds that depend on open habitats for feeding or nesting, shelter belts can reduce available space and also increase exposure to predators.
Why is tree placement important?
The study does not suggest that trees are generally harmful. Instead, the researchers emphasize that where trees are planted can make a big difference.
Adding trees to agricultural lands changes the structure of the environment, and while these changes may favor some species, they may create difficulties for others.
“Biodiversity-friendly farmland management must balance structural complexity with the ecological needs of open habitat types, especially in landscapes where wetlands have already been greatly modified by humans,” Hisano said.
Researchers say this is particularly important because many conservation efforts promote tree planting without fully considering the effects on entire bird communities.
What might future conservation plans look like?
The research team believes future studies should examine how shelter belt characteristics, including their width, height, spacing, arrangement and tree species, affect wildlife.
They also want to better understand indirect effects, such as whether shelter belts alter predator activity or affect the way animals move across the landscape.
“Ultimately, our goal is to help design evidence-based agri-environmental policies that work in wetlands around the world. Rather than promoting a single solution, such as planting more trees everywhere, we aim to support landscape-level planning that integrates open habitats and woodland features in ways that sustain diverse bird communities and the ecosystem functions they provide. By doing so, agricultural wetlands can remain productive for humans while continuing to serve as vital habitats for wildlife in a rapidly changing world,” Hisano said.
The study underscores an important lesson about conservation: Protecting nature doesn’t always mean adding more of something. Sometimes maintaining the balance between different habitats helps wildlife survive.
FAQ
Do trees always help birds?
No, some species may lose their habitat.
What are shelter belts?
Rows of trees used as windbreaks.
