James Lange remembers the day he and a team of botanists and conservationists gathered at a rock formation surrounded by a thicket of mangroves in Key Largo, Florida. They came to the country’s last wild stand of a rare cacti to face the inevitable. With sea level rise bringing the Atlantic Ocean closer and closer to the dying plants, the group made the difficult decision to remove the cacti’s remaining green material, preserve it in nurseries and hope that it could one day be reintroduced into the wild become
Three years later, research published last week reveals what Lange and the others have long suspected: The demise of the Key Largo tree cactus is the first recorded case of sea level rise driving a native species to extinction in the United States. Its collapse was a blow to Lange, a research botanist at Fairchild Tropical Botanic Garden in Coral Gables who co-authored the study. “That was one of the things that made the Keys so special,” he said. “Just a big, bold, beautiful plant.”
Tree cactus is a suitable name for Pilosocereus millspaughii, known for reaching towering heights, producing white flowers that attract nectar-hungry bats and producing reddish-purple fruit for birds and mammals to feast on. Although the cactus still grows on a few scattered islands in the Caribbean, it was limited to a single population in North America, a thriving stand of 150 plants discovered in the Florida Keys in 1992. By 2021, only six diseased strains remained.
It’s a monumental loss, scientists say, in no small part because of what it means. Anthropogenic planetary warming no longer only endangers human communities. It is wiping out the species that make up the fabric of our natural world.
“This existential threat that everyone is aware of, to see the actual evidence of it happening, which gives an expectation of what we can expect going forward, is important,” said Lange. He remembers how “everything just looked awful”, as the sea quickly entered the cluster of plants. “We just knew there was no long-term hope for this population in this area,” he said. “There is no shortage of plants in the Keys that are threatened with the same fate.”
Some of the critically endangered Large pine partridge pea after the jumping prickly appleany number of coastal species in the Florida Keys could be wiped out next one of the places most vulnerable to sea level rise. And unlike the Key Largo cacti, which, if only rarely, survive elsewhere, several of them are the last of their kind.
“It’s very worrying,” said Marcelo Ardón, who studies coastal ecology at North Carolina State University. “Climate change exacerbates all these different drivers making these populations even more vulnerable.”
A big herbivorous eventin which a significant amount of the plants were eaten by animals highlights the Key Largo cactus species in 2015. (Researchers suspect that this may have occurred due to tidal flooding that caused a shortage of fresh water, a bunch of thirsty raccoons or other game to gnaw at the trunks.) The threat was magnified by a subsequent series of recurring king tidesin addition to storm surge and damage caused by Hurricane Irma. Jennifer Possley, lead author of the new study, sees this as a possible “watchdog for how other low-lying coastal species will respond to climate change.”
But on a planet reformed by heating, plants are not the only populations facing an imminent threat of extinction. A decade ago, the Center for Biological Diversity identified 233 federally protected species in 23 coastal states as most at risk from sea level rise. The Key Deer, Bald Sea Turtle, Delmarva Peninsula Fox Squirrel, Western Snowy Plover and Hawaiian Monk Seal topped that list. Today, recovery efforts kept these five endangered species of being extinguishedbut their future is increasingly in questionas each remains threatened by habitats surrender to rising sea.
Globally, climate change has already led to the extinction of flora and fauna ranging from the Bramble Cay melomys, a rodent in Australia that the first confirmed mammal driven to extinction by global warmingafter the “functional extinction” of elk corals in the Keys and various marsh species in Germany. Some estimates suggest that, if emissions continue on their current trajectory, approx one in three species of animals and plants may become extinct by 2070.
The loss of any species to climate change is something plant physiologist Lewis Ziska feels deeply. Saying goodbye to the Key Largo tree cactus in particular is all the more meaningful to the scientist, who vividly remembers admiring the spiny cacti when he visited the Florida island chain. “It’s a beautiful plant, it’s very inspiring,” said Ziska. “So when you see it’s gone, there’s a sense of loss, almost a mourning.”