Study projects plant extinction rates through 2100

No matter how fast a species under threat can move, escape can only be successful if the new destination can meet its needs.

An ecological modeling study from the University of California, Davis, found that 7% to 16% of global plant species studied are expected to lose more than 90% of their range, facing high risk of extinction by 2100 under current climate change projections.

The study, published today in the journal Science, said habitat loss due to climate change is expected to drive these extinctions, not a plant’s ability to shift locations or “keep pace” with the changing climate.

This suggests that conservation strategies focused on assisted migration, where people facilitate species range shifts, may not reduce global plant extinctions induced by climate change. However, combining such efforts with restoration and protecting climate change refugia may be more effective. 

“We found that what causes extinction is not that plants aren’t moving fast enough,” said senior author Xiaoli Dong, an associate professor with the UC Davis Department of Environmental Science and Policy. “It is that a large amount of suitable habitat by the end of the century is going to be gone. If our priority is reducing the extinction rate of plant species, aggressively cutting our emissions will be much more important than other actions.”

Plants on the move

The researchers wanted to understand how plants are going to respond to warming over the next few decades. Where will they go? How many will go extinct, and what drives that extinction? To answer those questions, they leveraged a large database of nearly 68,000 plant species, which make up 18% of the world’s flora. They projected the distributions of these plants through 2100 and accounted for uncertainties, arriving at an extinction rate of 7% to 16% across emissions scenarios.

Most previous models projecting extinction rates do not incorporate the speed of range shifts — how fast species can actually move as the climate changes. This addition showed that habitat loss, not range shifts, drives extinction rates under climate change. 

High extinction rates are projected in southern Europe, the western United States and southern Australia, posing risks to both ancient and economically vital plant species. Among them are spikemoss (Selaginella) in California — one of the oldest surviving lineages of vascular plants, dating back over 400 million years — and eucalyptus in Australia, a genus that covers three-quarters of the continent’s native forests and is crucial to biodiversity, Indigenous culture and the timber industry. 

Pockets of increased diversity

Range shifts can, however, enhance local species richness, which refers to the number of species in a given place. About 28% of Earth’s surface will see an increase in local species richness as plants move in response to climate shifts, the study found. 

“Areas likely to gain species richness are mostly in wet regions or those projected to become wetter such as the eastern United States, India, Southeast Asia and southern South America,” said first author Junna Wang, a Ph.D. student when the study was conducted and currently a postdoctoral researcher at Yale University. “In contrast, the western United States, much of Europe and Australia are expected to lose diversity as many species’ ranges shrink.” 

‘Things will be different’

 This grand reshuffling of plants across the globe will require new ways of thinking about conservation and what “belongs,” Dong said.

“Things are going to change, and we have to adapt,” she said. “Some of these species will be meeting together for the first time. We will see novel interactions. The outcome of that is hard to predict. Things will be different from what we remember 40 to 50 years ago.” 

The study also highlights an increasingly important role for seed banks, botanical gardens and places that can serve as climate refugia for plants whose genetic, medicinal and cultural value may otherwise be lost. Meanwhile, stewarding ecosystems will help provide a place for species on the move to find a home. 

The study was funded by the National Science Foundation. 

Additional coauthors include Brunno Oliveira of UC Davis and Centre for Synthesis and Analysis on Biodiversity in France, Frances Moore and Daniel Kozar of UC Davis, and Yongshuo Fu of Beijing Normal University.