Change.Land use will complicate 'climate velocity' as a threat to species

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https://www.scientificamerican.com/article/suburbs-and-farms-team-with-global-warming-to-threaten-wild-animals-and-plants/?responsive=false

 

Not long ago, the idea that climate change could prompt whole ecosystems to move was introduced to researchers as "climate velocity." It's meant to show how quickly trees, plants and animals will have to migrate to find friendly temperatures.

Now a new analysis is estimating the pace of species movement because of both climate change and land use, revealing new pressures that stem from local decisions to build, plant and cut on the warming landscape. The speed of transformation is shown in the mountainous West, the Great Plains and the urban East.

The changes shown through 2050 could lead to lost habitat, the isolation of some species and the rise of "dispersal barriers"—like a wall of new development that prevents plants and animals from migrating. Overall, the study estimates that land use could prompt species to move at 10 kilometers (6.21 miles) per decade.

The study, published this week in the journal Nature Climate Change, suggests that some tough decisions could be ahead: Some areas might see tougher zoning restrictions, while others could be faced with relocating species that can't move on their own.

Overall, land use puts less pressure on species than climate change, the study found. Nationally, the 10-kilometer-per-decade velocity for land use is about 10 times slower than the climate velocity of about 100 kilometers per decade. But those calculations can change when analyzing smaller regions.

"The patterns varied quite a bit across the U.S. There are some areas that tend to have relatively high rates of climate speeds. There are others that tend to have relatively high rates of land-use change," said Jack Williams, an author of the study and the director of the Center for Climatic Research at the University of Wisconsin, Madison.

Other places have both
The study shows a map with a splash of red from south to north in the nation's center, depicting an area that's sensitive to both intensifying land use and climatic changes. The authors suggest this Midwestern strip could experience large changes to its landscape even as climbing temperatures force species to seek more comfortable habitats.

"A lot of times we focus on sea-level rise and fires in the West" as illustrations of climate change, Williams said. "But I think these analyses also point to the interior as being a point of concern."

In the Northeast, the researchers project a ratio of high species movement from land use as compared to climate change, based on its already dense development and large population. And west of the Rockies, the analysis predicts low movement from climate and land-use pressures. One reason for that is species tend not to travel as far in mountainous areas to reach cooler conditions.

The paper doesn't provide policy recommendations, but Williams notes that areas that are currently less developed, like the Midwest, might consider land-use plans that preserve "habitat connectivity" so species can move.

More severe outcomes could prompt stronger responses, like land acquisition to preserve habitat.

"Perhaps you want to think about things such as assisted migration, helping maybe relocating populations as climates change," Williams said. "If they change too fast for species to move, you may want to consider facilitated species movements across the landscape."

Climate velocity was first established in 2009 in a study estimating that species would have to move about a quarter-mile a year on average over the next 85 years. This week's research suggests a bigger movement of about 6 miles a year because of climate and about 0.6 mile annually because of land-use pressure.

David Ackerly, a climate biologist at the University of California, Berkeley, who participated in the 2009 study, said the new research provides valuable insight into other factors that can exacerbate the impacts of climate change.

"It's a really important step to be able to think simultaneously about both land-use change and climate, because there has been a real tendency to really black box them—to think about one or the other," he said.

Species may move, land use will be slow to change
It also raises some knotty questions about species movement. The climate impacts alone are confounding, given the diversity of species, landscapes and local environments in the United States. For example, Ackerly notes that species won't just move north to find cooler temperatures. He points to the influence of the Pacific Ocean, which can make winters warm in California and summers cool.

"You might have to move in different directions," he said.

Different topographies have their own characteristics.

Consider, for instance, a mountain bug: It could potentially move a few hundred yards up a mountainside to stay within its thermal zone. That's a low climate velocity. But a prairie plant in the Midwest, where many miles of land have a similar temperature, might have to travel much farther to remain in its preferred habitat.

The study also wades into a debate fraught with political undertones. It says that climate forces on species are stronger than land-use impacts. In a related field, property insurers say human development far outweighs the influences of climate change when it comes to rising damage from thunderstorms, flooding and hurricanes. In other words, the targets being damaged have multiplied faster than the storms' strength.

"Maybe locally you could have much higher rates of land-use conversion and spread in some areas" than climate velocity, Williams said. "But if you zoom back out and look at the U.S. as a whole, or even whole regions, these analyses do suggest that the rates of climate change might be faster at a national perspective."

In some areas, the climate speed could outpace the ability of species to move, he said.

Still, land use in some ways might be a trickier challenge to understand, and maybe even solve, than climate change, said Ackerly. He described climate as a straightforward scientific issue that's based on well-known principles: Carbon dioxide prevents heat from escaping.

Land use, however, is controlled at the local level in environments with unique characteristics across urban, agricultural and a multitude of other settings.

With climate change, Ackerly said, the country could pass legislation to address it. That's not likely for land use.

"You can't set a national policy to reduce land use," he said.