Revision of the flora of Desecheo Island, Puerto Rico

Studies of the flora of Desecheo Island can be divided into three periods: 1913-1914, 1967-1970, and 1994-1997. Visits to the island and herbarium studies showed that the reports of the two earlier studies were not complete. Of 161 species known from the island 36 are new reports. The greatest number of species (137) was collected in Period II. Fifty-two species known from Period I or II were not found in Period III and are assumed extirpated. Seven additional species were lost during Period III. Species turnover and loss were primarily among widespread herbaceous or semiwoody taxa. The high rate of colonization is attributed to Desecheo's proximity to a source island (Puerto Rico), a high visitation rate by both migratory and pelagic birds, and high levels of predation and disturbance. Species loss between Periods II and III is primarily attributed to overgrazing by feral goats, and to a lesser extent by rhesus macaques, exacerbated by two hurricanes and a prolonged drought. Degradation of the flora is expected to continue unless the exotic animals are eliminated.