In a heartbreaking first for the United States, a rare species of tree cactus has gone extinct in Florida due to rising sea levels. The Key Largo tree cactus (Pilosocereus millspaughii), which was confined to a single population in the Florida Keys, is now lost.
The Key Largo tree cactus was first discovered in 1992 in the Florida Keys, a chain of islands off the southern tip of the state. Since its discovery, researchers have monitored its population intermittently. However, saltwater intrusion from rising seas, soil erosion from storms and high tides, and herbivory by mammals put immense pressure on this delicate species.
Once thriving with around 150 stems in an isolated mangrove forest, the population had dwindled to just six fragile fragments by 2021. Researchers made a last-ditch effort to save the species by relocating these remaining fragments for off-site cultivation. Despite their efforts, the Key Largo tree cactus could not survive in its natural habitat.
“Unfortunately, the Key Largo tree cactus may be a bellwether for how other low-lying coastal plants will respond to climate change,” said Jennifer Possley, the director of regional conservation at Fairchild Tropical Botanic Garden. Possley is the lead author of a study documenting the decline of the species, published in the Journal of the Botanical Research Institute of Texas.
While the Key Largo tree cactus is extinct in Florida, it continues to grow on a few scattered Caribbean islands, including northern Cuba and parts of the Bahamas. These plants can reach heights of over 20 feet (six meters) and have cream-colored flowers with a garlic scent that attract bat pollinators. Their vivid red and purple fruits are also highly attractive to birds and mammals.
Human-caused climate change is the driving force behind rising sea levels. Water from melting ice sheets and glaciers flows into the world’s oceans, and as ocean water warms, it expands slightly. Both factors contribute to the rising seas that have now claimed the Key Largo tree cactus.
This tragic loss serves as a stark reminder of the impacts of climate change on our planet’s biodiversity and highlights the urgent need for conservation efforts to protect other vulnerable species.