Small Urban Greening Projects Can Greatly Increase Insect Species Numbers in Cities

Insects provide many essential benefits to ecosystems, including pollinating crops and flowers, helping to maintain healthy soil and recycling nutrients. They also keep populations at healthy levels through their own food chains.

A new project by researchers from the University of Melbourne has found a way to increase insect species numbers in a small urban greenspace by seven times, illustrating the importance of urban greening projects, a press release from the British Ecological Society said.

“The detrimental effects of environmental change on human and non-human diversity are acutely manifested in urban environments,” the authors of the study wrote. “We show how a small greening action quickly led to large positive changes in the richness, demographic dynamics and network structure of a depauperate insect community. An increase in the diversity and complexity of the plant community led to, after only 3 years, a large increase in insect species richness, a greater probability of occurrence of insects within the greenspace and a higher number and diversity of interactions between insects and plant species.”

The study, “Large positive ecological changes of small urban greening actions,” was published in the journal Ecological Solutions and Evidence.

Starting in the spring of 2016, the research team began turning a grassy urban lawn with two trees in Melbourne, Australia, into a habitat for a dozen species of indigenous plants. The team used soil decompaction, fertilization, new topsoil and organic mulching to create the urban oasis.

Over the course of the next three years, the researchers conducted 14 insect surveys, collecting samples of bees, wasps, ants and other insects, for a total of 94 insects, 91 of which were endemic to Victoria.

“The indigenous insects we documented spanned a diverse array. Detritivores that recycle nutrients, herbivores that provide food for reptiles and birds; predators and parasitoids that keep pests in check,” said ecologist and entomologist Dr. Luis Mata, the study’s lead author, in the press release.

During the study, the 12 species of indigenous plants started to support more and more insects. Three of the plant species were lost over the course of the study, but the nine that remained were able to support approximately 7.3 times as many insects as the two species that were originally occupying the urban greenspace.

Planting a more diverse array of flora in urban areas brings numerous rewards, including habitat and food for animals, lowering temperatures inside the city and mental health benefits for humans, as well as helping to mitigate climate change.

According to the press release, the method used by the researchers can be adapted and used on multiple sites, in different seasons and for longer periods of time. Thus, its benefits can be reaped by urban planners and scientists all over the world.

“I’d love to see many more urban greenspaces [transformed] into habitats for indigenous species,” Mata said in the press release. “We hope that our study will serve as a catalyst for a new way to demonstrate how urban greening may [affect] positive ecological changes.”