Lawns cover 163,000 square
kilometers of the United States, making grass the largest irrigated crop in the
country. As much as ecologists consider them biological deserts that Americans
should be encouraged to eliminate from their properties, it is unlikely lawn
cover will decline any time soon.
So urban ecologist Susannah Lerman
at the U.S. Forest Service’s Northern Research Station in Amherst, Mass.,
decided to figure out how to make lawns “less bad” by examining how lawns could
serve to provide habitat to declining populations of bees.
“While not everybody uses herbicides
on their lawn, the thing almost everybody does is mow,” Lerman said. “We
wondered if there were ways we can tweak this behavior to make it less bad for
bees. You see a lot of dandelions and clovers growing spontaneously. Do these
plants have ecological value as bee habitat?”
In an assessment of the natural
history of 16 suburban lawns in Springfield, Mass., she found that lawns that
were not treated with herbicides or pesticides yielded an unexpectedly rich
abundance of bee species and an equally impressive variety of what Lerman calls
“spontaneous flowers” – those that are not intentionally planted but which
provide nectar and pollen to bees and other pollinators.
After visiting each yard 12 times
over two years, she was surprised to discover 64 flowering plant species
spontaneously growing in the lawns, including violets, creeping Charlie, hairy
rockcress, purple smartweed and dwarf cinquefoil. “You go into these yards and
at first glance it looks like there’s nothing there,” she said. “But then you
start looking and there’s a lot more in there than you think.”
Even more surprising, Lerman and
colleague Joan Milan identified 111 different species of bees on the
properties. “It was astonishing!” she said. “We recorded a quarter of all the
bee species ever found in Massachusetts on these 16 suburban lawns. One yard
had 53 species of bee.” Strangely enough, the most abundant species was a type
of sweat bee not recorded in the state since the 1920s.
Lerman’s study also found that bees
were most abundant on lawns mowed every two weeks, compared to those mowed
weekly or every three weeks.
“Clearly there is value in these
landscapes for habitat conservation,” Lerman said. “Private yards shouldn’t be
ignored when thinking about conservation.”
To improve habitat for bees and
other pollinators, she said that homeowners should consider reducing or
eliminating the use of pesticides and herbicides on their lawns, plant a meadow
or pollinator garden if possible, and encourage the growth of spontaneous
plants in their lawn.
The latter suggestion may be
difficult for some people to follow, Lerman said. “Most people look at
dandelions and clovers and see them as weeds. We need to change their
perceptions and show that those plants are really providing wildlife habitat.
“And if you mow less often, you’ll
have more lawn flowers and more bees,” she added. “It’s a way to do less but
feel like you’re making a difference even though you didn’t spend any extra
time or money.”
This article first appeared in the summer 2017 issue of Northern Woodlands magazine.
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