Prospects for the long-term persistence of a severely endangered plant, Consolea corallicola (Cactaceae)

Abstract

The semaphore cactus, Consolea corallicola, is an endangered tree cactus endemic to just two sites in the Florida Keys. Since the 1980s, it has been threatened by the arrival of an invasive cactus-eating moth, Cactoblastis cactorum, rot, and, more recently, by sea level rise. Between 1996 and 2017, we outplanted 641 propagated cacti at 10 different sites in the Lower Keys and 632 cacti at 19 sites in the Upper Keys in an effort to increase the population size. Some sites were actively managed, and others were not. Persistence of outplanted cacti was poor, with no long-term survival at 17 sites and low survival at most others. Cactoblastis accounted for 9% of deaths, but crown rot, caused by a pathogenic fungus, Fusarium oxysporum, was the leading cause of death, accounting for 77% of mortality. Elevated soil moisture likely contributes to the high levels of crown rot. Cages to protect cacti from Cactoblastis and fertilization to alleviate the effects of crown rot did not increase survival rates. Observed saltwater intrusion and storms killed an additional 6% and 4% of cacti, respectively. Taken together as a whole, increased water levels and soil moisture are likely responsible for 87% of the mortality of our outplanted cacti. Cacti at actively managed sites did not survive better than those that were not actively managed. Given the likelihood of increasing sea levels, storm strength, and storm frequency, future strategies to save this iconic plant from extinction should include more outplantings at higher elevation sites, with as many individuals as possible, on higher ground with more consideration given to the ecology and genetics of its close relatives.