Drought could wipe out most of the habitat for a quarter of all cactus species

Cacti are the textbook survivors of dry country, which makes a new forecast about drought hard to shrug off. A University of South Florida-led team reports in Nature on Nov. 11 that when severe drought is built into habitat models, more than a quarter of nearly 1,000 cactus species could lose at least 80% of their suitable habitat by the end of the century.

Read next on Morning Overview: Neanderthals in Spain carved a wooden object that matches nothing archaeologists have ever found

Michiel Pillet, a postdoctoral researcher at USF, is lead author. Brian Maitner, a USF assistant professor of integrative biology, is a co-author, as is Pablo Guerrero, a botany professor at Universidad de Concepción in Chile. Brian Enquist, a plant ecology professor at the University of Arizona, is senior author. The U.S. National Science Foundation funded the work, and scientists in Chile, Peru, Mexico and Cuba contributed.

Adding severe drought to the habitat models

Standard projections lean on long-term averages of temperature and rainfall, which miss extremes such as droughts, hurricanes and cold snaps. Pillet said extreme events are usually left out of large-scale forecasts, and that his team folded newly available global drought projections into the models in a new way, according to the USF release on EurekAlert. The team combined those data with biodiversity databases, field observations and the community science network iNaturalist.

The Nature paper used 648,316 curated occurrence records for 993 cactus species. Models that included severe drought were better supported than mean-climate models in 91% of cases, the abstract reports.

The five scenarios span the Shared Socioeconomic Pathways from SSP1-2.6, a low-emissions path, to SSP5-8.5, a high-emissions one, so the ranges below are spreads across possible futures rather than a single forecast. The gaps are large. With a 100-kilometer dispersal limit, the share of species losing any suitable area rose from 58-61% to 69-72% once drought was included, across scenarios from SSP1-2.6 to SSP5-8.5. The share losing over a quarter of their area rose from 26-43% to 55-58%. The share losing over four-fifths rose from 1-15% to 25-35%, which is the band behind the quarter-of-species figure.

Put plainly, the share of cacti facing an 80% habitat loss goes from at most 15% under averages alone to between 25% and 35% once drought is counted. The lower end of that band is the quarter in the study’s framing, and the upper end approaches a third of the family.

Chile, Peru and northeastern Brazil

The release singles out cactus hotspots in Chile, Peru and northeastern Brazil as likely to see especially severe losses. The paper reports that five bioregions could lose more than a quarter of their species, though the text available for this article does not name them.

Losses of that size could qualify many species as Critically Endangered under IUCN criteria, which would more than double the number of cacti in that category. More than 30% of cactus species are already threatened, including most species in Florida, mainly through habitat destruction and poaching.

Maitner said the team was skeptical at first, but cactus experts across North and South America confirmed what they were already seeing in the field. Guerrero said some populations are already losing habitat and nearing extinction risk because of climate and extreme events. Enquist voiced concern that even drought-adapted plants may face substantial losses of suitable climate. The authors suggest other plant groups could show similar effects once extreme weather enters the forecasts.

Plant scientists tend to assume a desert specialist is the safe bet in a warming world. The new models suggest the opposite for a large slice of the family, because a plant adapted to scarce water is still tuned to a narrow band of conditions, and a run of severe drought years can push a site outside that band. Pillet noted that conventional range models, which rely on averages, would never register that kind of event.

Dispersal limits and an earlier, milder estimate

Whether cacti can move matters a great deal. When the authors restricted dispersal from 100 kilometers to zero, the share of species losing suitable area under severe drought climbed from 69-72% to 84-85%.

The result builds on earlier work by Pillet. The 2022 paper, Elevated extinction risk of cacti under climate change in Nature Plants, assessed 408 species under three emissions pathways and projected that about 60% would lose favorable climate, with roughly 31% of cacti already threatened. A news account in EcoWatch of that work said global warming could raise extinction risk for 60 percent of cactus species by mid-century, but the study did not consider extremes such as droughts and wildfires. TheScienceBreaker’s summary of that analysis reported that nearly a quarter of species would lose over 25% of their range, against 55-58% in the new drought-inclusive models.

These are projections of suitable climatic habitat, not counts of dead plants, and the outcome depends on emissions and dispersal. Pillet noted that impacts are already limiting plant ranges and that the results will feed into updated IUCN Red List assessments of cacti.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.