Research Reveals Surprising Ecological Benefits of Non-native Bombax ceiba

A common theme in improving biodiversity is a push for native plants over exotic plants. However, exotic plants can have a role to play in enhancing a habitat. Silva and colleagues have recently published an example in the journal Urban Ecosystems. This research reveals the ecological role of an alien tree, the Bombax ceiba, also known as the Cotton Tree, in supporting the biodiversity of nectar-feeding birds in urban areas whilst posing a low risk of adverse impacts on the environment.

The term ‘alien’ or ‘exotic’ species often sparks concerns about their potential negative impacts on local ecosystems. This research turns the tables, showcasing how an alien tree species can benefit urban ecosystems. Specifically, Silva’s team found that the Bombax ceiba tree acted as a nectar resource “hub” for 38 different bird species in an urban area in Brazil. This variety of birds included those that consumed nectar as well as other floral parts, implying the tree’s significance as a source of diverse nutrition.

Despite being alien, the Bombax ceiba demonstrated only a moderate risk of negative impacts on native species and ecosystems. This research highlights the importance of not only considering a plant’s origin but also its function in planning biophilic, or nature-loving, cities through urban greening.

It’s not just quantity that makes Bombax ceiba a keystone food plant. There’s also timing. It attracts a large number of bird species during the dry season when food sources are typically scarce. Being a source of abundant nectar, the Bombax ceiba supports a broad ecological spectrum of birds, providing them with essential nutrients during a period of food scarcity.

Additionally, the presence of this tree in urban areas not only boosts the biodiversity and ecological stability of the city but also encourages a closer human-nature connection. Watching and photographing the variety of birds attracted to these trees can provide urban dwellers valuable recreational and educational opportunities.

Risk analysis carried out by Silva’s team concludes that any potential invasion threat from Bombax ceiba is moderate and not associated with an irreversible decline in native species populations. In their article, they write:

Our assessment indicates that the alien B. ceiba has considerable importance for the urban bird community of a tropical town. Its importance is highlighted by the high number of birds attracted, their diverse habits and roles, and the daily production of large quantities of nectar with high caloric content during food scarcity periods. Bombax ceiba is likely to attract birds and other native animals to cities of varying sizes and degrees of urbanization. For example, the sampled trees compose typical environments of all cities, i.e., peri-urban green areas and mostly street verges. Our assessment, therefore, supports the selection of B. ceiba as a tree resource for different built environments, particularly as street trees, which are of great value in providing food resources for urban birds (Wood and Esaian 2020; Liu and Slik 2022).

Silva et al. 2023.

This research serves as a valuable reminder that not all alien species pose a threat to biodiversity. In fact, some, like Bombax ceiba, can become unlikely heroes in urban environments, offering a lifeline to a host of local species whilst enhancing the ecological balance and human-nature connection. As our cities continue to grow, such insights may be critical in planning our urban landscapes in a more biodiverse, sustainable, and enjoyable manner.

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Silva, P.A., Cherutte, A.G., Gomes, A.C.S., Silva, L.L., Brito, L., Rodrigues, B.M. and Maruyama, P.K. (2023) “The ecological role and potential impact of an alien tree highly attractive to native nectar-feeding birds in urban areas,” Urban Ecosystems. Available at: https://doi.org/10.1007/s11252-023-01345-9.