Climate change, sea level rise causes Key Largo cactus extinction – Palm Beach Post

The last known stronghold in the country of the towering Key Largo tree cactus was a limestone island in an isolated mangrove forest, where it bloomed garlic-scented flowers in anonymity for ages unknown.
But beset by a brackish water assault in a warming world, the cactus, discovered in 1992, withered.
It is now believed to be the first local extinction of a species caused by sea level rise in the United States, according to researchers from Fairchild Tropical Botanic Garden in Coral Gables and multiple state and local agencies.
A study published Tuesday, July 9, in the Journal of the Botanical Research Institute of Texas chronicles the demise of the lone stand of Key Largo tree cactus, which had a robust 150 stems growing to 20 feet tall when it was first chanced upon three decades ago.
By 2021, there were just six sickly fragments of the cactus left. When it was clear those would not survive, scientists collected them, hoping to keep its legacy alive in a nursery setting.
“I liken it to losing a piece of historical artwork,” said Jennifer Possley, director of regional conservation at Fairchild Tropical Botanic Garden and the lead author on Tuesday’s report. “It’s a part of our story and in this case, it’s a charismatic part of our natural history. It’s a cool plant, and it’s gone now.”
The Key Largo tree cactus does still grow in the Caribbean, including parts of the Bahamas. Its creamy white flowers reflect moonlight, attracting pollinators such as bats and sphynx moths. It bears purple seed-rich fruits for birds or furry locals.
On its solitary post in Key Largo, the cactus also fell victim to hurricanes, including 2017’s Hurricane Irma, which left areas of the island flooded for weeks with harmful saltwater. Unknown critters preyed on the cactus, possibly drawn by its high water content when freshwater was scarce, scientists said.
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But Possley said she believes the cactus could have withstood the occasional hurricane and critter if it weren’t for encroaching sea levels that increasingly caused flooding king tides in the fall months and stole soil from the cactus’ limestone footing.
“Most of the other rare plants we work with aren’t just growing in a single site,” Possley said. “The sea level rise was the nail in the coffin for this one.”
According to the Florida Climate Center, sea level rise in the Southeast United States has been about 0.12 inches per year since the early 1990s, but it varies by area.
At Virginia Key, an island off Miami that is about 50 miles north of Key Largo, sea levels have risen 8 inches since 1950. And that trend is accelerating. Sea levels have been rising by 1 inch every 3 years over the past 10 years, based on tide gauge data.
A 2022 report from the National Oceanic and Atmospheric Administration predicts sea levels along U.S. coastlines will rise, on average, 10-12 inches through 2050, which will be as much as the rise measured over the 100 years leading up to 2020.
“We are on the front lines of biodiversity loss,” said Key Largo tree cactus study co-author George Gann in a prepared statement. Gann is executive director for the Delray Beach-based 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,” Gann said.
Other co-authors of Tuesday’s report include researchers from the Florida Department of Environmental Protection and the U.S. Department of Agriculture.
Extirpation is the loss of something in a localized area. Extinction means the loss of something on a more global scale.  
The Center for Biological Diversity found in a 2013 study that 233 threatened and endangered species in 23 coastal states are at risk from sea level rise, including the endangered Key Deer.  
“This means that, left unchecked, rising seas threaten the survival of 17 percent — one out of six — of our nation’s federally protected species,” the report notes.
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When first discovered, some scientists thought the stand of Key Largo tree cactus was a unique population of the similarly named Key tree cactus. The Key tree cactus was listed as federally endangered in 1984, and between 1994 and 2007, its population decreased by 84%.
The two plants look alike with tall stems and similar flowers. But the Key Largo variety has long tufts of woolly hair at the base of its flowers and fruits. Spines on the Key Largo cactus are also twice as long as they are on the Key tree variety.
In 2019 the Key Largo tree cactus was confirmed to be the first and only known flora of its kind in the United States, according to a study by Alan Franck, the herbarium collection manager at the Florida Museum of Natural History.
Possley said there are tentative plans to plant some of the nursery-grown Key Largo tree cactus in the wild. She said they have thousands of seeds, multiple tall plants and have found an area where they could potentially grow outside the nursery.
“But there’s no spot left that is perfect,” Possley said.
Kimberly Miller is a journalist for The Palm Beach Post, part of the USA Today Network of Florida. She covers real estate and how growth affects South Florida’s environment. Subscribe to The Dirt for a weekly real estate roundup. If you have news tips, please send them to Help support our local journalism: Subscribe today.