Flickr/robynlou8

Pollinators and people both benefit when public grassy patches are allowed to grow long.

It's not just a bad time to be a pollinator; It's a bad time to be a human that eats.

In the U.S., up to 59 percent of honeybee colonies, 96 percent of bumblebees, and 90 percent of some monarch butterflies are in decline. These and other insects, birds, and even bats distribute pollen to nearly 75 percent of the world's crops, contributing upwards of $300 billion in economic value.

In tangible ways, pollinators conserve humans. So how can cities help conserve pollinators? One answer: In public parks, let the grass grow long.

That's what researchers at the University of Sussex have done, yielding win-win results for pollinators and park visitors alike. The team worked with the Brighton & Hove city council to leave sections of grass unmown at Saltdean Oval, a small suburban public park, to see how it might affect the growth of wildflowers, and in turn, the abundance of pollinators.

A map of Saltdean Oval.

In 2012, the researchers left the eastern grassy half of the park completely unmown (the other half continued to be cut for recreational use). Beginning in the spring of 2013, they designated four blocks of grass within that half, subdividing each block into four smaller strips. Each strip was treated with a different mowing pattern: One was mown every two weeks through the spring and summer; two were mown up until to different points in the summer; and the last was not mown at all.

The result was a more verdant, buzzing park. The strips left completely unshorn produced three times as many wildflowers as the strips that were regularly cut. And they attracted five times the number of insects, including honey bees, bumble bees, butterflies, hoverflies, and other essential pollinators.

The total numbers of insects counted visiting flowers or resting throughout the project period.

"All we did was give the wildflowers a chance," says Dr. Francis Ratnieks, a co-author of the paper detailing the project, published in Insect Conservation and Diversity. "The seeds were already in the ground, ready to burst out."

Abundance of flowering units in in different
mowing treatments.

The wildflowers weren't anything special. Lotus corniculatus, a common relative to the pea, popped out of the tall grass at the highest rate of any other flower. After that was Pimpinella saxifraga, a wild-growing member of the carrot family native to Britain. Next came Centaurea nigraa common daisy often treated as a weed—which attracted more bee species than any other plant, as shown in figure four. Ordinary as they were, the flowers still did plenty to lure in essential insects.

Ratnieks points out that these results won't necessarily be replicated everywhere; If a park has long used herbicide, it might be less likely to see significant growth as Saltdean did.

But, he says, uncut grass is worth investigation—particularly since it costs cities virtually nothing. With U.K. and U.S. parks budgets slashed at every level, letting sections of grass grow long makes economic sense. "A lot of people think you’ve always got to intervene with nature," he says. "But in many places, it's best to simply encourage what's already there."

Visitors to the well-trafficked park largely appreciated the unmown areas. In a survey, 97 percent said they approved of encouraging insects and wildflowers, and 26 percent said that the long grass actually increased their enjoyment of the park.

Swansea, Wales, also began an initiative to leave a smattering of parks partly uncut this past summer. It hasn't tracked the growth of wildflowers or insect visitation in these areas, but public response has been overwhelmingly positive, according to city councillor Sybil Crouch. Crouch helped to champion the initiative, which she says "wasn't rocket science. People have known for a long time industrial mowing isn't good for wildlife."

In the U.S. and U.K. alike, parks departments have tried encouraging insect visitors through butterfly gardens, wildflower meadows, and native grass patches. Yet few have taken this more passive—yet effective—approach to pollinator conservation.

Crouch credits her constituents. "I kept getting complaints from residents about how the parks department was mowing down all the bluebells," she says. "It's your job as a politician to recognize all of the ideas out in your city, and to try to make the good ones real."

Top image courtesy of Flickr user robynlou8.

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