Tiny street gardens in Amsterdam can support insects
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Tiny city gardens can be a haven for wildlife such as insects, a study of small city gardens in the Netherlands has found. The two factors that offer the biggest boost are having lots of plants and having lots of different types, but it makes no difference whether the plants are native or not.
“Even with these really small gardens, just planting a few plants can make a substantial difference,” says Joeri Morpurgo at Leiden University in the Netherlands.
While there have been some studies of biodiversity in large gardens, there are virtually none on small gardens, says Morpurgo. So in 2019, his team surveyed 65 urban front gardens in Amsterdam and The Hague that were less than 10 square metres in area.
The researchers measured factors such as the overall number of insects, the number of different species, whether plants were native or not, and the area covered by plants. Coverage was calculated by adding the areas spanned by individual specimens, so a garden could have a coverage greater than the area of land due to vegetation overlapping.
They found insect numbers and species richness correlated strongly with plant coverage and plant richness. But neither the size of the garden nor, to their surprise, the proportion of native plant coverage made any difference.
In theory, native plants should be better. Pollinating insects often have adaptions for particular flower shapes, while some plant-eating insects consume specific varieties.
There are several possible explanations for why the proportion of native plants made no difference, says Morpurgo. It could be that the insects that thrive in cities are generalists, for instance, or that many of the insects are exotic, too. The study didn’t classify insects as native or not.
Research on larger garden plots at Wisley in the UK has produced broadly similar results. “The more plant matter, the more invertebrates,” says Andrew Salisbury at the Royal Horticultural Society (RHS), who led those studies.
But one of the RHS studies did find that native vegetation can support a slightly higher abundance of plant-eating species such as caterpillars, says Salisbury.
Morpurgo says he would still encourage people to grow native species. “There are more benefits to native plants than just helping insects,” he says, such as their cultural value.
His main advice is do nothing, and just let plants – including those some call weeds – grow and attract wildlife. “Just leave everything as is, and nature will come around to your garden,” says Morpurgo.
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