16th April 2022
60% of cactus species impacted by climate change
A new study published in Nature reveals the likely impacts of climate change on cacti by mid-century.
When you imagine the kind of plants that might be endangered by a warming planet in the coming decades, cacti are unlikely to be the first that come to mind. Most already live in habitats with at least some drought, requiring evolutionary adaptations to conserve water. Some have been known to survive for as long as two years without rain or humidity. A fully-grown saguaro (Carnegiea gigantea) can reach more than 18 metres (60 feet) in height and its arms will store up to 200 gallons of water.
However, even these tenacious floras are not immune to the effects of climate change. A new study, led by the University of Arizona, concludes that the number of cactus species at risk of extinction "is projected to increase sharply in the future, especially in current richness hotspots."
The research team looked at range forecasts and diversity maps for 408 cactus species (about a quarter of the global total). Their detailed analysis showed that 60% of species will be negatively impacted by 2050–2070, with about 40% undergoing "significant declines".
Despite their popular image as thriving in deserts, cacti have a surprising variety of habitat ranges and evolutionary adaptations. Most occupy specialised niches making them sensitive to environmental changes. Some are found in cooler, high-altitude mountainous areas, others on low-lying coastal plains. Rainforests also contain many species. The study researchers note that epiphytes will endure the greatest exposure to increased warming. Epiphytic cacti are plants that grow on the surface of other plants (such as a branch or tree trunk). Unlike parasites, no harm is caused to the host, with moisture and nutrients instead being derived from the air or rain.
Most cactus species "are in some way adapted to the climates and environments that they live in," said Michiel Pillet, a conservation ecologist and PhD student at the University of Arizona who led the new study. "Even a slight change may be too much for them to adapt over shorter time scales."
For now, the main threats to cacti are from agricultural expansion, land degradation and harvesting for various uses. But in 30 to 50 years, a primary driver of extinction risk will be climate change, according to Pillet and his team.
Of the approximately 1,500 in the world, only a single cacti species is likely to benefit from climate change. Xique-Xique (Pilosocereus gounellei) is projected to increase its range and numbers in eastern Brazil. The most at-risk regions include other parts of Brazil, as well as Mexico and the U.S. state of Florida.
The rapid and ongoing loss of cacti will have a cascading effect on biodiversity and the food chain. The survival of many animals is dependent on the water, fruits, and flowers produced by cacti. Some birds, such as the cactus wren, even use these plants for nesting, roosting, and protection from predators.
Cacti are also important to humans – not just as ornamental houseplants, but also in food, drink, medicine, fabrics, and construction materials. The plants have long been taken for granted due to their perception as tough, well-protected organisms that survive in harsh conditions.
"It's a popular image of cacti," said David Williams, Professor of Botany at the University of Wyoming, who did not take part in this study. "'Ah, we don't have to worry about cacti. Look at them, they've got spines, they grow in this terrible environment.'" This is clearly a misconception, he said, describing the new research as "pivotal" for highlighting the scale of threat to cactuses. "There are a lot of these tipping points and thresholds and interactions that are very fragile and responsive to changes in the environment, land use and climate change."
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