New research finds that even cacti are severely threatened in a warmer, drier world

By Matthew Cimitile, University Communications and Marketing

Findings from a study spanning the Americas show that climate-change forecasts are underestimating threats to biodiversity - even to exceptionally resilient species - by not factoring in extreme weather events that become more likely in a warmer world.

New research published in Nature revealed a dramatic decline in suitable habitat for the majority of nearly 1,000 cactus species studied when incorporating severe drought data into existing climate distribution models.

An international team led by the University of South Florida (USF) and University of Arizona found that more than a quarter of cactus species analyzed could lose at least 80% of their suitable habitat by the end of the century. Projected diversity declines could be especially severe in important cactus diversity hotspots like Chile, Peru and northeastern Brazil.

This level of loss could qualify these cactus species as Critically Endangered, according to criteria established by the International Union for Conservation of Nature (IUCN), which would more than double the number of species currently in this category.

Authors of the study suggest similar impacts will be seen in many other plant groups when accounting for extreme weather events with future climate scenarios.

"Climate change makes extreme events more frequent, but such events are typically excluded from large-scale forecasts," said Michiel Pillet, lead author of the study and a post-doctoral researcher at USF St. Petersburg. "For this study, we integrated severe drought projections into models, which is quite novel, and extrapolated that at large scales with a plant family that is adapted to drought conditions. Our findings indicate that these adaptations may not be sufficient in a future with longer and more intense droughts."

Conventional distribution models typically rely on long-term temperature and rainfall averages but fail to capture the damaging effects of extreme events such as droughts, hurricanes and cold snaps on biodiversity. By incorporating newly available global data on future droughts with records from biodiversity databases, field observations and the community science network iNaturalist, researchers were able to improve predictions of future impacts.

"When we started modeling and crunching the data, we were really skeptical of the initial findings," said Brian Maitner, an assistant professor of integrative biology at USF St. Petersburg and co-author of the study. "Then we consulted with cactus experts across North and South America and they confirmed that what we were modeling, they were already seeing in the field."

While cacti are icons of desert environments, they inhabit nearly all types of ecosystems across the Americas, from California to Florida, and from Canada to the southern stretches of South America. More than 30% of cactus species are already threatened with extinction, including most species in Florida, particularly from habitat destruction and poaching.

Research published in 2022 by Pillet and Maitner already showed that climate change will elevate this number, but the addition of severe drought vastly increases how much suitable area species stand to lose.

"Cacti have evolved an astonishing range of forms and strategies that allow them to persist in some of the driest environments on the planet," said Brian Enquist, a plant ecology professor at the University of Arizona and senior author on the study. "But there is something deeply concerning about discovering that even these plants may face substantial losses of suitable climatic habitat due to extreme events."

The research was informed by a cadre of scientists across the Americas, including in Chile, Peru, Mexico and Cuba, and from institutions including the Desert Botanical Garden, Conservation International and the IUCN Species Survival Commission Cactus and Succulent Plants Specialist Group. The study was aided by additional data from iNaturalist.

"What we are seeing on the ground are some cacti populations that are already experiencing reductions in habitat and nearing extinction risks due to this combination of climate and extreme events," said Pablo Guerrero, a professor of botany at the Universidad de Concepción in Chile and co-author of the study. "The data and modeling allows us to reveal the extent of this surprising development across geographic scale and hopefully inform how we proceed in conserving and protecting what we can."

Researchers emphasize that further work is needed to understand how drought affects different life stages, in what ways species may respond to changing conditions and which other plant (or non-plant) groups may be similarly impacted. Nevertheless, the study demonstrates that accounting for severe drought can substantially change forecasts of biodiversity loss - and indicates a growing challenge to identify which species face the greatest risks of extinction when extreme weather events are considered alongside long-term climate trends.

"Though these forecasts are for the end of the century, it is important to note we are already seeing impacts that are limiting plant ranges today," Pillet said. "Our results will inform updated IUCN Red List conservation assessments, and we expect the outlook for cacti will be grim, especially when our projections are combined with ongoing threats of habitat destruction and illegal collection."