As cities expand globally, natural habitats are shrinking, leaving plant-animal interactions increasingly precarious. While green spaces are often scarce in highly urbanized areas, certain large, ancient trees, revered for cultural significance, persist. New research from the Wuhan Botanical Garden (WBG) of the Chinese Academy of Sciences now provides empirical evidence that these venerable trees serve as shelters and food sources for urban bird communities, even amid broader declines in bird diversity.

Published in Biological Conservation, the study challenges the notion that large old trees are merely aesthetic or cultural assets. Its findings position them as essential ecological components, critical to building more resilient and ecologically functional cities.

The researchers hypothesized that in intensely urbanized zones, a greater share of birds would depend on these large trees for sustenance and shelter, interacting with them for longer durations, despite an overall drop in avian diversity.

To test this, the team studied 30 representative large old trees in Wuhan, selected from the city's official inventory. The species included Cinnamomum camphora, Celtis sinensis, and Xylosma congesta, distributed across a wide urbanization gradient. During the autumn fruiting season, the researchers systematically recorded bird behaviors—passing, perching, and feeding—around each focal tree. In total, they documented approximately 5,000 bird individuals belonging to 41 species.

As anticipated, overall bird diversity declined with increasing urbanization. Conversely, the proportion of birds perching or feeding on the large trees rose significantly in more urbanized areas. Trees bearing more fruit attracted greater numbers of birds to perch and feed. The duration of each perching or feeding event remained consistent across the urbanization gradient but was slightly shorter in urban cores, likely due to higher levels of human disturbance.

"The ecological significance of these large old trees becomes more pronounced as we move toward urban centers," explained Prof. CHEN Sichong, corresponding author of the study. "Protecting each large old tree is akin to preserving miniature Noah's Arks of biodiversity within cities."

The study strongly advocates for recognizing the ecological value of large old trees as equal to, or even greater than their cultural and aesthetic worth. The researchers emphasize that protection efforts must go beyond symbolic measures such as plaques or heritage listings. Instead, they call for preserving the surrounding microhabitats and actively reducing human disturbance around these crucial urban oases.

This research was supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences.

Large trees in cities. (Image by WBG)

Study locations, design and tree-bird interaction. (Image by WBG)

Utilisation of large trees by birds along the urbanisation gradient. (Image by WBG)