February 27, 2022

Plants can’t adapt to climate change when seed-dispersing animals are lost | CBC Radio

A new study suggests the global decline of bird and mammal species has reduced the ability of plants to adapt to climate change by 60 per cent.

Half of the plants around the world need animals to spread their seeds. But with recent global declines in biodiversity, plants are less able to hitch a ride to better conditions as the climate warms.

“This is a number that should raise alarm bells,” said ecologist Evan Fricke, who led the study. “It’s indicating that the loss of animal biodiversity is putting our plant biodiversity at risk.”

The research was published Thursday in the journal Science.

Adapting to climate change by moving away

In a changing climate — with higher temperatures, rising sea levels and erratic weather — humans and wildlife will have to adapt by moving away from flooding coastlines or croplands without water.

Plants, too, will have to migrate in order to survive.

“Plants’ ability to cope with climate change, in part, depends on whether they can move to newly suitable areas that are suitable for growth. They might decline in their historic ranges, but hopefully new arrivals can survive under those changing conditions,” said Fricke.

For half the world’s plant species, that migration requires an animal to physically move the seed to a new location.

“That spans from birds eating berries, but also [to] cases like squirrels dispersing acorns, and things like burrs hitching a ride on everything from a rabbit to a rhino,” Fricke said. 

An American robin eats a winterberry. Small birds like robins typically disperse seeds over relatively short distances. (Paul D. Vitucci/Rice University)

For the study, Fricke and his team combined seed-spreading data from thousands of field studies conducted over several decades, which looked at how many seeds animals disperse, by how far, and how well those seeds germinate.

This information went into a machine learning model, which then compared the current level of seed dispersal to the level that would have been possible had animal populations remained at historical levels.

“When we look at that global scale, we estimate a 60 percent decline in seed dispersal,” said Fricke.

Biodiversity crisis accelerating climate change 

The study also showed that not all areas were affected equally by the decline of seed-dispersing animals. The loss was greatest in temperate regions across North America, Europe, South America and Australia.

Stan Boutin, a professor of population ecology in the University of Alberta, who was not involved in the research, said he was not surprised at the results of the paper. He said that Canada’s boreal forest isn’t as affected by the loss of seed-dispersing animals as other parts of the world. 

Ungulates like moose help to spread seeds in the boreal forest, but even where their populations have declined, white-tailed deer have moved in to fill in that role. (The Canadian Press/Jonathan Hayward)

“Most plant species in the boreal do not require gut passage to germinate,” said Boutin. “Plants have always had to deal with dispersal over long distances due to large fires. Even though fires can be large, given time, most if not all species, will recolonize the area burned, largely through wind dispersal of seed from unburned patches or areas surrounding a burn.”

Still, Fricke adds, the loss of animals that spread seeds may also work to accelerate climate change, which is a global problem.

“Seed dispersers, and especially large seed dispersers, are especially important for the dispersal of large seeded tree species,” said Fricke. “If we lose those species … then the carbon stored in our forests is likely to be less. And so with less carbon stored in our forests, that puts us at a disadvantage in trying to mitigate climate change.”

Produced and written by Amanda Buckiewicz.

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