The difficulties of single factor thinking in restoration: replanting a rare cactus in the Florida Keys

Abstract

The Florida Semaphore cactus, Opuntia corallicola, is a rare species with a distribution currently limited to one island in the Florida Keys. The only 12 mature, flowering individuals known to exist in 1989 were threatened by the arrival of an exotic cactus feeding moth, Cactoblastis cactorum. Cages were erected in 1990 around these cacti to protect them from Cactoblastis. From 1990 to 1998 the O. corallicola population was monitored and number of new recruits were measured. In May 1996, we made an outplanting of 96 small, new cacti derived from fallen pads, in an experimental regime designed to bolster the number of extant cacti and to test for the effectiveness of cages as a protection against Cactoblastis. Both the natural and the outplanted population declined by over 30% during our monitoring periods. In both the natural population and the experimental outplanting most individuals died because of what appeared to be stem browning, probably by a plant pathogen. The next largest cause of mortality in the outplanting was by trampling, probably by Key deer. Cactoblastis destroyed one mature cactus but killed no individuals in the outplanting. A hurricane in 1998 was a minor cause of death for outplanted individuals but killed two mature cacti.