Altitudinal Change in Plant Endemism, Species Turnover, and Diversity on Isla Santa Cruz, the Galapagos Islands

Abstract

Vegetation zones of Isla Santa Cruz in the Galapagos Islands range from the lowland dry zone, through transition and moist zones, to the highland zone, reflecting the precipitation pattern. The zones are deflected upward on the leeward north side, as compared with the windward south side. The brown subzone and Miconia robinsoniana scrub of the moist zone are absent on the north side. Zonation and species distribution patterns are also related to altitude and substrate. Floristic and phytosociological endemisms for woody species increase with higher altitude, while those of herbaceous species are low in high elevations because of low endemism in pteridophytes. Species turnover rate along the altitudinal gradient is three times higher on the windward south side than on the leeward north side. Species diversity is low in Scalesia pedunculata forest, where stand-level dieback has occurred as a consequence of the species-poor constitution.