The global climate crisis is wreaking havoc on temperatures and environments around the world: extreme heat in Death Valley has experts warning it could become the hottest place on record again, while rising sea levels have caused the first localized extinction of Key Largo’s tree cactus in the US.
Key Largo Tree Cactus (Pilosocereus myrspaugi) was only discovered in a small population in the Florida Keys in 1992. The species still grows in the Caribbean, in the Bahamas and northern Cuba. By 2021, the Florida population had declined from 150 to just six due to harsh weather conditions, saltwater intrusion and predation by mammals.
“Unfortunately, Key Largo’s arboreal cacti may be a bellwether for how other lowland coastal plants will respond to climate change,” Jennifer Posley, regional conservation director at Fairchild Tropical Botanical Garden and lead author of the study documenting the population decline, said in a statement.
Under good conditions, the species can grow to over 6 metres (20 feet) tall and produce garlic-scented flowers that reflect moonlight to attract bat pollinators. When first discovered, the Key Largo Tree Cactus was called the Key Tree Cactus (Pilothocereus robini), there has been confusion as to the identity of this new species. Although both species have purple and red fruits, there are important differences between the two.
“The most noticeable difference is the tufts of long hairs at the base of the flowers and fruit,” says Alan Frank, now manager of herbarium collections at the Florida Museum of Natural History. The hairs are so dense they make the cactus look like it’s covered in snowdrifts. The spines on the Key Largo cactus are also twice as long as those on the Key Tree cactus.
Key tree cacti are also in big trouble, declining by 84 percent between 1994 and 2007 and being listed as federally endangered in 1984. The two biggest problems facing these species appear to be herbivores and increasing salinity of the surrounding soils, especially caused by high ocean tides, or “king tides.”
A rescue operation began in February 2016, when researchers collected stem fragments to cultivate in nurseries. By 2021, it was clear that the population would not recover. During the last fruiting season, researchers were able to collect cactus fruits containing viable seeds. The green parts of the cactus were then harvested and taken to two nurseries. Currently, the population is limited to a captive collection of 36 salvaged fragments, 25 seedlings, and over 1,000 seeds in storage.
Researchers had no choice but to remove the cacti from the habitat to save the species.
Image credit: Trudy Ferraro
The team returned to the area in both 2022 and 2023 in the hope of collecting more samples that may have been missed. A small piece of debris was first discovered in 2023, but it was decided to remove it from the area as it was clear that it would be destroyed by rising sea levels.
Florida Keys species are particularly vulnerable to sea-level rise due to the low-lying nature of the land in the region. Extreme weather events, habitat destruction and poaching have all been implicated in declining populations of vulnerable species. The research team suggests that long-term conservation plans for other at-risk plants are already underway, and that protecting these species both in and out of situ will require collaboration at both the local and federal levels.
The paper appears in the Journal of the Texas Botanical Laboratory.