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City birds prefer native trees

While city trees contribute to a variety of important ecosystem services, such as lowering local temperatures and purifying the air, they are also home to large populations of birds and insects. To better understand how different types of trees affect birdlife, a team of researchers led by Lund University in Sweden has monitored 400 nest boxes in five parks in the Swedish city of Malmö during a period of seven years. 

The analysis revealed that native trees – defined as species that have been in the ecosystem for at least seven centuries – offer more resources and are generally preferred by city birds.

“Non-native trees, also known as introduced, exotic or alien species, lack an evolutionary history with the local ecosystem. We have previously shown that non-native tree species have substantially fewer insects than native trees, so the effect we are now seeing is probably a result of a shortage of food for insectivorous birds, such as the great tit,” said study lead author Johan Kjellberg Jensen, a PhD student in Urban Ecology at Lund.

Introduced tree species are increasingly common in urban planning all over the world. For instance, in the city parks of Malmö, approximately one in four trees are non-native. Although the introduction of such trees is advocated by some scientists since they are more tolerant to the harsh conditions of cities, it is crucial to understand the consequences of their presence for local ecosystems.

“If you want to hear more birdsong in spring, I think the choice of urban trees is an important factor. If you increase the number of native trees in city parks and green spaces, our local birds are more likely to thrive,” Jensen explained.

These findings confirm the results of previous studies focused on the effects of tree origin in North America and highlight the importance of maintaining native trees in urban parks. “I hope that city planners and other stakeholders take note of this research and that we together can develop strategies to ensure a functioning ecosystem in our cities,” Jensen concluded.

The study is published in the journal Oecologia.


By Andrei Ionescu, Staff Writer

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