Increasing the number of plants in cities provides a big and rapid boost to biodiversity, according to a four-year study in Melbourne, Australia. The findings add to the evidence that the greening measures many cities are starting to take can make a huge difference to wildlife, in addition to their other benefits.
鈥淎dding more indigenous plant species to a small green space聽can greatly contribute to positive ecological outcomes in a short period of time,鈥� says at the University of Melbourne.
Around the world, many efforts are under way to try to green cities. In 2020, the UN Food and Agriculture Organization launched , which supports measures such as tree planting. In the European Union, the initiative is encouraging city planners to do more to green cities.
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Proponents of such efforts list many benefits: improving physical and mental health by reducing air pollution, providing a better environment and encouraging people to get out more; helping keep cities cooler as the climate gets warmer; boosting social interactions and, of course, increasing biodiversity.
But there is surprisingly little scientific evidence that urban greening projects boost biodiversity. The evidence that exists is based on comparing areas with different numbers of plant species, says Mata. As far he is aware, his team鈥檚 study is the first to measure biodiversity in a city area before it was greened and then how it changed afterwards. The study involved 14 insect surveys done over four years.
鈥淭his is the first study to track how ecological benefits accrued across the lifespan of a specific urban greening action,鈥� Mata says.
The study was of a small green space in Melbourne, Australia, just 200 square metres in size. The site, which is adjacent to a major road and surrounded by large buildings, just had two gum trees on a kikuyu lawn before greening. Twelve indigenous plant species were added.
A year later, there were five times as many insect species. After three years, there were seven times as many, even though three of the added plant species had died out. Overall, the team recorded 94 insect species at the site, almost all of which were indigenous.
鈥淚 can鈥檛 think of any drawbacks,鈥� says Mata. 鈥淥n the contrary, the indigenous plant species require less water and don鈥檛 require fertilisers.鈥� Now they have grown to cover most of the ground, there is also no more need for weed control, he says.
鈥淭his report demonstrates the ability of healthy plant and fungi communities to provide the building blocks for ecosystems abounding with biodiversity,鈥� says , head of UK conservation charity Plantlife, which has been campaigning to boost wild flowers and wildlife simply by encouraging individuals and city officials to mow lawns, parks and road verges less often, or to mow at better times.
The key is to allow wildflowers to go to seed before mowing, says Dunn. 鈥淲here plants lead wildlife follows, and bees and butterflies are returning to some previously inhospitable terrains thanks to laudable urban greening efforts,鈥� he says.
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