It's Time to Retire Grass Lawns if We Want to Stop Species Extinction

Urban "stepping stones" can help biodiversity thrive.

Public Domain Pictures

Humans have not been great stewards of the natural world. According to a landmark report released last week, 1 million of Earth’s species are at risk of extinction, and biodiversity is declining at an unprecedented rate. This deterioration of the environment has been driven by human actions, but according to new research in the journal Ecology, we can try to make some amends — starting by sharing our homes.

Urban and suburban areas are often written off as inhospitable to wildlife — but that doesn’t mean they don’t have potential. Major U.S. cities have between 19 and 69 percent green space, compared to an average of 19 percent in European cities. This means there’s already a lot of green space in the US, even in cities. The issue is how these spaces are used: As of now, they mostly consist of traditional grass lawns and non-native ornamental plants.

The Ecology study, published on Tuesday, argues that if these areas are transformed to include strategic “stepping stones” of high-quality habitat, humans can help certain species persist. Study first author and Tufts University professor Elizabeth Crone, Ph.D., tells Inverse that by converting wildlife-unfriendly landscapes, like lawns and paved areas, to spaces that include wildlife-friendly things like native plants, humans can provide necessary food and habitat resources for animals.

“I think we — both scientists and people in general — under-appreciate the importance of how ‘non-habitat’ affects the ability of species to persist on the landscape,” Crone says. “We need to be thinking about the conservation value of suburbs and cities and farmland, as well as parks and nature preserves.”

The Baltimore checkerspot butterfly quickly moves through spaces with 15 percent high-quality habitat.

Wikimedia Commons

At the center of this study is the knowledge that climate change affects the movement of species in a number of ways — whether that means shifting the range of their existence to higher latitudes to avoid rising temperatures, or moving to a space where there is less competition for resources. This team theorized that improving the habitability of landscapes that species are shifting their ranges to can help slow the pace of species extinction.

In turn, after evaluating 70 studies that focused on the range movements of 70 different species, they found that in 73 percent of cases, animals can quickly move through “lower-quality” habitats. There’s a trade-off here: Moving quickly through a site to breeding grounds is good, but moving through low-quality habits (like cities) can be very dangerous.

To examine this idea further, they examined the range expansion rate of the Baltimore checkerspot buttery. They found that its expansion rate — how quickly it migrates through a space to a breeding ground — was fastest in landscapes that are composed of around 15 percent high-quality habitat and 85 percent unsuitable habitat.

The problem is, on average, suburban and urban areas don’t have that percentage of high-quality habitats. But the study authors emphasize that creating these habitats is a realistic and achievable goal: If landscape planners think more about creating these helpful pockets, they don’t need to worry so much about keeping unbroken tracts of natural areas. Instead, they can create a mix of high-and-low quality spaces, promoting movement and population growth.

A yard in California containing native plants.

Flickr/California Native Plant Society

One way to do this, Crone says, is to incorporate lots of native plant species into our yards and cities. Many plant nurseries have sections marked with pollinator-friendly plants, and many states have native plant societies that can advise you on what to grow in your garden. Crone notes that there are even companies that sell garden kits that show you how to arrange your native plant garden in the most aesthetically beautiful way.

Subsequently, you can end up with a yard that helps support biodiversity — and could end up making your life easier in the short-term as well.

“If you get the right plants for your region,” Crone says, “my experience as a gardener is that they take less effort to maintain than a traditional lawn.”

Ecologists often assume that range expansion will be fastest in landscapes composed entirely of the highest-quality habitat. Theoretical models, however, show that range expansion depends on both habitat quality and habitat-specific movement rates. Using data from 78 species in 70 studies, we find that animals typically have faster movement through lower-quality environments (73% of published cases). Therefore, if we want to manage landscapes for range expansion, there is a trade-off between promoting movement with nonhostile matrix, and promoting population growth with high-quality habitat. We illustrate how this trade-off plays out with the use of an exemplar species, the Baltimore checkerspot butterfly. For this species, we calculate that the expected rate of range expansion is fastest in landscapes with ~15% high-quality habitat. Behavioral responses to nonhabitat matrix have often been documented in animal populations, but rarely included in empirical predictions of range expansion. Considering movement behavior could change land-planning priorities from focus on high-quality habitat only to integrating high- and low-quality land-cover types, and evaluating the costs and benefits of different matrix land covers for range expansion.
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