Key Largo cactus goes extinct in U.S.

The Florida Keys has long been the frontline when it comes to the effects of climate change, and the chain of islands has had its first casualty in the war with sea-level rise.

Monroe County sea-level rise projections estimate between 10 to 21 inches of rise by 2040, 21 to 54 inches by 2070 and 40 to 136 inches by 2120. However, the damage is already being felt in various areas of the Keys, whether it is humans, animals and now plants.

The United States has lost its only stand of the massive Key Largo tree cactus in what researchers believe is the first local extinction of a species caused by sea-level rise in the country, according to a recently released study. The now-extinct species in the United States was once found at John Pennekamp Coral Reef State Park in Key Largo.

The Key Largo tree cactus (Pilosocereus millspaughii) still grows on a few scattered islands in the Caribbean, including northern Cuba and parts of the Bahamas. In the United States, it was restricted to a single population in the Florida Keys, first discovered in 1992 and monitored intermittently since, according to the study, which was published in the Journal of the Botanical Research Institute of Texas.

Salt water intrusion from rising seas, soil depletion from hurricanes and high tides, and herbivory by mammals put significant pressure on the population, the authors of the study stated. By 2021, what had been a thriving stand of about 150 stems was reduced to six ailing fragments, which researchers salvaged for off-site cultivation to ensure their survival.

“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 on a study published Tuesday, July 9, that documented the population’s decline.

UNCERTAIN IDENTITYComparatively little is known about Florida’s rare cacti. Researchers initially stumbled upon the Key Largo tree cactus in an isolated mangrove forest, and for several years afterward, its identity remained uncertain. Most considered it to be a unique population of the similarly named Key tree cactus (Pilosocereus robinii), a federally endangered species that is present elsewhere in the Florida Keys.

The two cacti have a similar appearance. The stems of both shoot up perpendicular to the ground and can grow to be more than 20 feet, according to researchers who conducted the study. Both have cream-colored, garlic-scented flowers that reflect moonlight, attracting bat pollinators, while their bright red-and-purple fruit catch the eye of birds and mammals.

But there are key differences as well, which made Alan Franck, currently the herbarium collection manager at the Florida Museum of Natural History, suspect they were dealing with something unique on Key Largo.

“The most striking difference is the tuft of long, woolly hairs at the base of the flowers and fruits,” Franck said. The hair is so thick, it can look as though the cactus is covered in drifts of snow. Spines of the Key Largo cactus are also twice as long as they are on the Key tree cactus.

In 2019, Franck confirmed that the Key Largo population was the first and only known instance of Pilosocereus millspaughii in the United States.

By then, it was succumbing to some of the same environmental pressures that had plagued its relative, the Key tree cactus, during the last century. The latter was once common throughout the area, but its numbers have dipped dangerously low.

But there are key differences as well, which made Alan Franck, currently the herbarium collection manager at the Florida Museum of Natural History, suspect they were dealing with something unique on Key Largo.

Writing in 1917, botanist John Small noted that the Key tree cactus “was for a long time very abundant [on Key West] … In recent years, with the destruction of the hammock for securing firewood and for developing building sites, this interesting cactus has become scarce, until at present it is on the verge of extermination in its natural habitat.”

The Key tree cactus was listed as federally endangered in 1984, but its numbers continued to wane. Between 1994 and 2007, it decreased by 84%.

Researchers at Fairchild began monitoring all of the tree cactus populations annually in 2007, working in tandem with local land managers. One Fairchild-led study showed that salt levels were higher in soil beneath dead verse living cacti in the years following a storm surge event in the Lower Keys, drawing a clear connection between mortality and increased salinity.

Researchers also initiated a robust conservation collection for these species. Potted cacti are grown at a facility in Coral Gables, Florida, and seeds from both wild and cultivated plants are carefully banked for long-term conservation.

The Key Largo tree cactus grew on a low limestone outcrop surrounded by mangroves near the shore at the state park. The site originally had a distinct layer of soil and organic matter that allowed the cactus and other plants to grow, but storm surge from hurricanes and exceptionally high tides eroded away this material until there wasn’t much left.

Salt-tolerant plants that had been previously restricted to brackish soils beneath the mangroves slowly began creeping up the outcrop, an indication that salt levels were increasing.

Given enough time, these changing conditions would likely have killed the cactus. But other incidents occurred that hastened the pace.

“We noticed the first big problem in 2015,” said study co-author James Lange, a research botanist at Fairchild. When he and his colleagues arrived to evaluate the plants that year, half of the cacti had died, apparently as a result of an alarming amount of herbivory. Cacti store reserves of water in their succulent stems, which allows them to survive for long periods of time without rain. This makes them enticing to animals when other sources of water are scarce.

“In 2011, we started seeing saltwater flooding from king tides in the area,” Lange said, referring to particularly high ocean tides.

“That limits the amount of freshwater available to small mammals and might be related to why the herbivores targeted this cactus, but we can’t say for sure. We’d never seen cactus herbivory like this anywhere in the Lower Keys, where flooding has tended to be less extensive.”

The team set out cameras in hopes of finding the culprit, but whatever it was did not return, and there was no evidence of significant herbivory thereafter. Yet, when the team came back the following year, roughly another 50% of the population had died. In response, staff from Fairchild and the Florida Department of Environmental Protection took a few cuttings of what remained to grow in greenhouses.

The decline of the Key Largo tree cactus and the necessity of its removal has given researchers an idea of what to expect in the future as species contend with a rapidly warming world, the researchers stated. Instead of a smooth, predictable rise in sea or salt levels, the reality of climate change is messier and manifests itself in a complex series of related events that put additional pressure on species that are already stressed.

“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.”

Lange called the extinction “one more tangible effect” of climate change and sea-level rise.

“On some scale, this is a data point,” Lange said. Lange could not quantify what the cactus’ extinction will be on the Key Largo ecosystem, but the cactus was a lush food source and did flower.

“Every species plays a role and when you lose one, you will have an impact,” Lange said. “This is not to say that this was a keystone species and this will have a cascading effect.”

KEYS-WIDE IMPACTSSalt water intrusion and flooding has become a growing problem in the Keys. The U.S. Fish and Wildlife Service, which oversees the National Key Deer Refuge and Crocodile Lake National Wildlife Refuge, published a paper in 2022 entitled “Outrunning Climate Change,” which documented refuge managers’ efforts to address sea-level rise and protect some of the creatures that call the refuges home.

Crocodile Lake National Wildlife Refuge managers have helped crocodiles deal with climate change. Crocodiles either dig holes in the sand or build mounds out of sand, pebbles and shrubs, before laying their eggs. In the climate-troubled, mangrove-rich Keys, sandy beaches are increasingly hard to find. Old crocodile breeding grounds succumb, increasingly, to the rising sea, according to refuge managers.

In the past 15 years, the U.S. Fish and Wildlife Service, along with state, federal and non-profit partners, built 40 maternity wards for expectant crocodiles on the refuge. Placement of the 5-foot-long, 2-foot-tall sand mounds is critical: they must be far enough from the marauding salt water, yet close enough to the nutrient-rich mangrove swamps for hatchlings. Once an egg hatches, the mother will carry her baby to the nearby pond, cove or creek.

At a crescent-shaped tract of land on the refuge, refuge managers constructed 20 berms from construction-grade sand. During last year’s nesting season, between March and May, crocodiles occupied three of the berms. The refuge crew tagged more than 40 hatchlings — a testament to pro-active, climate-fighting, wildlife management tactics.

Monroe County government obtained a $75,000 matching grant from the state last year to study the impacts of sea-level rise on Keys plants and animals and their habitats, according to Monroe County Chief Resilience Officer Rhonda Haag. Tree cactus was among the list of species identified for study, she said.

The study is “wrapping up,” and the goal is to come up with “strategies” to “make the natural environment for resilient,” Haag said, adding, “The county is concerned and is coming up with plans to protect habitat.”.

Sea-level rise is not just a problem for Keys plants and animals, but residents as well.

There is no other neighborhood in the Florida Keys that has been impacted by sea-level rise and flooding in recent years as much as Stillwright Point in Key Largo. Flooding on residential streets there can last for weeks and, in turn, can keep deputies from patrolling sections of the neighborhood and the mail from being delivered to some homes. Flooding sometimes forces Keys Sanitation to put a Dumpster at the end of certain roads because the company’s trucks will not drive down the street, according to neighbors.

Stillwright Point residents have regularly spoken at Monroe County Commission meetings to lobby for the county to move more quickly on road improvement projects in their neighborhood.