Insects flock to green island in the city

An urban greening project has transformed a small parcel of land, squashed up against a construction site and a major road in Melbourne’s CBD, into a hive of activity for insects.

Replanting a degraded patch of land with indigenous vegetation led to a 7-fold increase in the diversity of insects according to research spanning 4 years (2016 to 2019) and involving 14 insect surveys.

The study published in Ecological Solutions and Evidence provides a snapshot of how a small greening action in a densely urbanised environment can bring about large positive ecological changes.

Lead author Dr Luis Mata says this demonstrates the ecological benefits of urban greening, and provides evidence to local governments, residents and landholders that efforts to restore even small patches of land are worthwhile.

The study focuses on insects as the animal group which responds the quickest to changes in plant structure or composition.

Mata says the 200 m² site originally had a very deteriorated and trampled lawn with a couple of trees.

Melbourne City Council selected the site to be purposefully replanted with indigenous plants as part of a memorial recognising significant Aboriginal men, Tunnerminnerwait and Maulboyheenner. 

Mata says this “little island” was replanted with a mix of plants, shrubs and grasses indigenous to Melbourne city. 

The survey which looked at specific insects occurring or living on each individual plant species, shows more types coming to the site after the replanting.

“By year one there was already a sharp increase in species. And it was even more pronounced by year three,” Mata says. 

The insects which came the first year, stayed at the site. “There was a shift from colonisation to actually survival at the site … so insects were staying there and living there” he says.

The study also documents significant increases across different functional groups of insects – herbivores, detritivores, predators and parasitoids. “Particularly those last two,” Mata says are important. “Because these are the types of beneficial insects that you would want to be attracting to a green space. They will control pests and they will keep things in balance and healthy.”

He says the study was made possible by scientists collaborating with practitioners, in this case, the City of Melbourne.

“We were happily surprised,” Mata says. “We did our study in probably the worst conditions possible, in terms of distance to other green spaces and level of urbanisation. And even so we found this big sharp response.”