(CN) - Cities will grow exponentially in decades to come, and while wildlife conservation has seldom factored into city planning, a pair of studies found Thursday that urban centers can play a key role in the preservation of the monarch butterfly.
Monarchs, with their stunning orange and black wings, are some of the most recognizable pollinators. But their numbers have dwindled in the United States, declining over 80% in the last twenty years.
Scientists link the decline of monarchs to the widespread loss of milkweed, an important food source for the butterfly and the only plant it can lay its eggs on.
In two studies published Thursday in the journal Frontiers of Ecology and Evolution, researchers said that cities can aid in the preservation and continued existence of the monarch by planting milkweed, the only host plant for the iconic species.
Milkweed, often viewed as a common weed and ripped from gardens and commercial fields, produces fragrant and nectar-rich flowers that attract pollinators of all sorts. But monarch caterpillars feed exclusively on its leaves.
The study, produced with support from the U.S. Fish and Wildlife Service, scanned the available land in urban areas and found that the best chance for boosting milkweed is to grow it in people’s backyards.
Mark Johnston, a conservation ecologist at the Field Museum in Chicago, said in a statement that to preserve the monarch species, cities would need to plant at least 1.8 billion stems of milkweed, an endeavor that would cover an area the size of Washington, D.C.
"This approach to examining metropolitan landscapes allows us to 'see' cities in a way we haven't been able to before, and this enables us to get a better estimate of how much potential space there is to create habitat," Johnston said, adding that cities’ efforts would add 15 to 30 percent of the milkweed that's needed to save the butterfly species.
Abigail Derby Lewis, an ecologist at the Field Museum, said in a statement that monarchs would be boosted by even the smallest habitat expansion in cities, which comprise only 3% of U.S. landmass.
“There's an assumption that cities are not important places for plants and animals,” Lewis said. “But that's because no one had looked at these landscapes in a systematic way or at the collective impact from many small-scale plantings across large urban geographies."
By embracing their role in conservation, cities can shift the public’s perspective on protecting wildlife that “aren't as beloved by the public as butterflies,” Derby Lewis said, adding that beetles - vital pollinators for key crops like apples and avocados - would also be boosted by cities’ conservation efforts.
While the native milkweed plant is not technically a weed, researchers said more work is needed to have people embrace the plant’s presence in backyard gardens.
"I would encourage people to question the grassy lawns that dominate our urban landscape,” Johnston said. “Could we plant something else that would provide habitat for monarchs and other wildlife?"
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