Newshot 
The humble cactus is an icon of resiliency. Stuck in a desert with little rain and abundant searing sun, these plants don’t just survive, they thrive—and in turn provide habitat for owls and other birds, and flowers for bats and other pollinators.
Yet cacti are in serious trouble, due to habitat loss and the poaching of species for private collections. Now we can add worsening droughts to those woes, according to a new study in the journal Nature. Researchers modeled a future of not just relentlessly rising temperatures but also the attendant dry spells, finding that the majority of nearly 1,000 cactus species will lose habitat as the climate radically changes. More than a quarter of those species could lose at least 80 percent of that habitat by 2100.
“The public perception of cacti tends to be of these organisms that are extremely drought-adapted and are just resilient, can handle anything that you throw at them,” said Michiel Pillet, a conservation ecologist at the University of South Florida and lead author of the paper. “In reality, cacti are absolutely amazing—and they’re my favorite plant group, clearly—but they’re not that different from other plants.”
That means cacti need water. In the deserts of the southwestern United States, for example, they rely on seasonal monsoon rains, which tend to make July or August the wettest month in a given year. Because this is still a desert, cacti have evolved a range of adaptations to survive, like a waxy skin that helps them retain that bounty of rainwater. “Just like other plants, they evolved under conditions that they’re used to,” Pillet said. “When you take them outside of those conditions, they might not be able to handle that.”
Think of these cacti like sick hospital patients. Someone might be admitted for heat-related illness, as their body struggles to cool itself. At the same time, though, they might be dehydrated. Cacti are dealing with the same stresses, as global temperatures rise and dry spells intensify. “When we consider drought conditions, then it turns out that they’re much, much sicker than we previously thought,” Pillet said. “These results really do change the outlook of cacti, and most likely plants more broadly under climate change.”
Instead of simply modeling these threats going forward, the researchers turned to the citizen science platform iNaturalist, where people upload photos of plants and animals. This provided 650,000 observations of cacti in the wild, helping paint a clearer picture of how species might be faring.
Really, this isn’t a simple matter of cacti withering and dying. Sure, if relentless droughts take hold, individuals can’t get water. But the stress could be temporally complex, too. “Now we can move towards questions of: What life stages are most affected?” Pillet said. “Is it the adults or is it the seedlings? But also, which processes? Is it reduced growth or is it increased mortality? Or are plants failing to flower?”