Accidental urban oases

Abstract

As some cities struggle with population declines, vacant lots are proliferating. Can these derelict spaces contribute to conservation? The bumblebees of southeast Michigan are wary of downtown living. Certainly, they buzz around city gardens and nature reserves—but numerous buildings and concrete structures nearby these green spaces typically mean fewer bumblebees and bumblebee species. When it comes to vacant urban lots, some see blight, others havens of conservation. Researchers found that vacant Baltimore lots are home to 60 bird species, including American robins ( Turdus migratorius ). Image courtesy of Christine Brodsky. Except, that is, in Detroit. In the state’s biggest city, bees seem relatively unfazed by urbanization. One downtown garden site boasts nearly as many bumblebees as a nature reserve in a rural area (1). “We see this huge bounce-back in the abundance and diversity of these important pollinators,” says ecologist Paul Glaum at the University of Michigan in Ann Arbor, MI, who was part of the bee survey behind this counterintuitive discovery. What is so special about Detroit? The city is filled with vacant residential properties, where houses sit empty or have been demolished. Partly because of the decline of US car manufacturing, Detroit’s population fell from about 1.8 million people in 1950 to less than 675,000 in 2016. Departing residents left behind yards that became overgrown. When Glaum walked around the city in 2014 and 2015, he saw wildflowers thriving in many of these vacant lots, perhaps because city workers mowed infrequently and didn’t apply herbicides to the sites. But where some might see a mess of unkempt weeds, Glaum sees a vital refuge for bees. Other studies, too, suggest a surprising amount of biodiversity in abandoned urban spaces. Researchers have found that vacant lots—ranging from the yards of unoccupied homes to old industrial sites—can harbor rich communities of plants, …