A COMPARISON OF UNGRAZED AND LIVESTOCK-GRAZED ROCK VEGETATIONS IN CURACAO

Five of the largest remaining patches of livestock-inaccessible rock v egetation of Curacao, Netherlands Antilles, were described and compare d to rock vegetation which has experienced centuries of livestock graz ing. Study rocks (maximum diameters: 20-47 m) were located at two site s differing in rock type and altitude. At the St. Christoffelberg site , study rocks were siliceous and at altitudes of 240-310 m while at th e Tafelberg site the rocks were of limestone and at altitudes of 35-15 0 m. The main vascular species on livestock-inaccessible rocks at both sites was Tillandsia flexuosa, a bromeliad. At the St. Christoffelber g, Tillandsia was principally accompanied by the grass Paspalum secans , the orchid Brassavola nodosa and the herb Portulaca venezuelensis, w hile at the Tafelberg it was principally accompanied by the vine Serja nia curassavica. On livestock-accessible rocks Tillandsia ground cover was reduced to insignificant levels and mature plants were virtually eliminated from the population. Grazed vegetations also showed reduced vascular cover and were principally dominated by the annual grass Ari stida adscencionis (St. Christoffelberg site only), the prickly pear O puntia wentiana and the shrubby tree Acacia tortuosa, None of these we edy species, all of which are widely distributed on the island, were o f any significance in ungrazed rock vegetations. It is hypothesized th at Tillandsia-dominated ground cover may have been a common feature of the rock vegetation of the island prior to the introduction of livest ock.