Florida tree cactus is the first extinction victim of rising seas in the United States

key largo tree — The large white flowers of the Key Largo tree cactus have a mild scent reminiscent of garlic and reflective white petals and reproductive tissue that helps pollinators find them by moonlight. Credit: SUSAN KOLTERMAN.

A rare species of tree cactus has gone extinct in Florida. This marks the first known extinction attributed to sea level rise in the United States, researchers reported on Tuesday.

A Silent Warning from Nature

The U.S. population of the Key Largo tree cactus, scientifically known as Pilosocereus millspaughii, was found only in the Florida Keys. It was first discovered in the area in 1992 and was monitored sporadically for decades.

However, rising seas brought saltwater intrusion and soil erosion from storms and high tides, putting immense pressure on the small population. Additionally, wild mammals would often eat the cactus, adding to the strain.

By 2021, the population had dwindled from 150 thriving stems to just six struggling fragments.

Photo of cacti damaged by Hurricane Irma — The population on Key Largo sustained heavy damages during Hurricane Irma in 2017 and afterward struggled to recover. Credit: James Lange.

So, researchers attempted to save the remaining plants by relocating them for off-site cultivation. Despite these efforts, the species could not survive the environmental changes. It’s now officially the first species in the United States whose extinction has been pinned to sea level rise — and it won’t be the last.

“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, director of regional conservation at Fairchild Tropical Botanic Garden and lead author of the new study that documents the population’s decline.

Staff from Fairchild and the Florida Department of Environmental Protection removed all remaining green material in 2021 after it became clear the population was not going to survive. Credit: Jennifer Possley.

Our Changing Ecosystem

The Key Largo tree cactus, while extinct in Florida, may still grow on a few Caribbean islands, including northern Cuba and parts of the Bahamas. The Key Largo tree cactus is considered to be a unique population of the similarly named Key tree cactus (Pilosocereus robinii) that grows in the aforementioned areas.

It can grow up to 6 meters (20 feet) tall, with cream-colored flowers that attract bats and vivid fruits that appeal to birds and mammals. Key Largo cactus spines are about twice as long as they are on the Key tree cactus. Its hair is also thicker, making the Key Largo tree appear like it’s covered in drifts of snow.

Human-caused climate change is accelerating sea level rise. The melting of ice sheets and glaciers, and the thermal expansion of seawater are the core of this phenomenon. This combination poses a significant threat to low-lying coastal ecosystems.

The extinction of the Key Largo tree cactus in the U.S. serves as a stark reminder of the immediate impact of climate change. This event raises critical questions about the future of other low-lying coastal plants. As the planet continues to warm, the need for conservation efforts becomes more pressing.

“We are on the front lines of biodiversity loss,” said study co-author George Gann, executive director for the Institute for Regional Conservation. “Our research in South Florida over the past 25 years shows that more than one-in-four native plant species are critically threatened with regional extinction or are already extirpated due to habitat loss, over collecting, invasive species and other drivers of degradation. More than 50 are already gone, including four global extinctions.”

The findings appeared in the Journal of the Botanical Research Institute of Texas.