The last remaining stand of the Key Largo tree cactus (Pilosocereus millspaughii) has been wiped out, marking what is believed to be the first local extinction of a species due to sea level rise. While not endemic to the Florida Keys, the native range of this species once extended from Florida to the islands of The Bahamas, northern Cuba, Haiti, and Turks and Caicos.
Key Largo Tree Cactus in the United States
The Key Largo tree cactus is a tall, tree-like cactus that can grow up to 10 meters (about 33 feet) in height. It features ribbed, blue-green stems covered in sharp spines, which branch out from a central trunk, creating a canopy-like structure. This cactus is adapted to the subtropical climate of the Florida Keys, thriving in dry, rocky soils often found in tropical hardwood hammocks and pinelands.
Historically, the Key Largo tree cactus was found in a single population in the Florida Keys, first discovered in 1992. It grew on a low limestone outcrop surrounded by mangroves, a habitat that provided the specific environmental conditions the cactus needed to survive.
Two similar cactus species
The Key Largo tree cactus is not the same species as the Key tree cactus (Pilosocereus robinii) although they share similarities. Both are tall, columnar cacti in the Florida Keys, and they share several other similarities, such as their vertical growth, spiny stems, and nocturnal flowers that attract bat pollinators.
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The Key Largo tree cactus, distinguished by its dense tufts of woolly hairs around the base of its flowers and fruits, has longer spines and a more limited distribution, being confined to a single population in Key Largo before its extirpation. In contrast, the Key tree cactus, which lacks the pronounced woolly hairs and has shorter spines, is found in multiple locations throughout the Keys, although it is also endangered.
The Key Largo Tree Cactus succumbs to sea level rise
Recently, the United States lost its only remaining stand of this massive cactus, marking what researchers believe to be the first local extinction of a species in the country directly attributable to sea level rise.
In 2011, 150 individual cacti were still living. By 2015, this number had declined to 60 individuals and by 2016 this number was further reduced to 28 rooted stems. In 2021, it was determined by conservationists that the Key Largo tree cactus was no longer viable in the wild and the last remaining six individuals were harvested and sent to two locations for cultivation: Fairchild Tropical Botanic Garden and John Pennekamp Coral Reef State Park.
Subsequent field surveys in 2022 and 2023 found no evidence that the Key Largo tree cactus was viable in the wild. A study documenting the demise of the Key Largo tree cactus due to sea level rise was published in 2024 in the Journal of the Botanical Research Institute of Texas.
Environmental pressures hastened the local extinction of this cactus
The Key Largo tree cactus has been subjected to multiple environmental threats over the years, leading to its eventual extinction in the wild in the United States. One of the most significant pressures was saltwater intrusion from rising sea levels, exacerbated by storm surges and exceptionally high tides. These conditions depleted the soil and increased salinity, which, over time, degraded the cactus’ habitat.
Hurricanes, particularly Category 5 Hurricane Irma in 2017, and subsequent king tides further eroded the remaining suitable habitat for the cactus.
In addition to the physical impacts of climate change, the cactus also faced significant herbivory, likely driven by small mammals seeking water during periods of saltwater flooding. This herbivory severely damaged the cactus population, further hastening its decline.
A bellwether for other plant species
The extinction of the Key Largo tree cactus is seen as a bellwether by conservations when it comes to the broader impacts of climate change on low-lying coastal species.
Conservationists have initiated efforts to grow the cactus in controlled environments, such as greenhouses, and there are tentative plans to reintroduce some individuals into the wild.
However, the long-term survival of the species remains uncertain. The suitable environments for tree cacti, such as the narrow fringe between mangroves and upland hammocks known as thorn scrub, are rapidly disappearing. This decline underscores the urgent need for broader conservation efforts to protect not just individual species but entire ecosystems.
Researchers note that the challenges faced by the Key Largo tree cactus may be indicative of what other coastal plant species will encounter as climate change continues to alter habitats. The complex and interconnected nature of these environmental changes—rising sea levels, increased salinity, and more frequent and intense storms—creates a challenging scenario for conservationists attempting to preserve biodiversity.
References
Pinson, J. (2024, July 9). First local extinction in the U.S. due to sea level rise. Florida Museum.
Possley, J., Lange, J. J., Franck, A. R., Gann, G. D., Wilson, T., Kolterman, S., … & O’Brien, J. (2024). First US vascular plant extirpation linked to sea level rise? Pilosocereus millspaughii (Cactaceae) in the Florida Keys, USA. Journal of the Botanical Research Institute of Texas, 18(1), 211-223. DOI: 10.17348/jbrit.v18.i1.1350
Fonte : National Geographic
