SERPENTINITE, HARZBURGITE, AND VEGETATION ON SUB-ANTARCTIC MACQUARIE ISLAND

Macquarie Island (54-degrees-35'S, 158-degrees-55'E) is a subantarctic island composed of oceanic crustal rocks lifted above sea level during the middle to late Pleistocene. The northern third of its plateau contains large areas of serpentinite and harzburgite. Outcrops of basalt rich in phenocrysts of olivine and pyroxine occur farther south. Where large enough to influence soil formation all these areas are marked by sparse vegetation cover with small, apparently slow-growing plants and a high percentage of bare ground, in sharp contrast to adjacent areas. Soils and plants on serpentinite and harzburgite areas contain high nickel and magnesium, and have lowered calcium/magnesium ratios. There are no species confined to the serpentinite and harzburgite rocks and none is a hyperaccumulator of nickel, presumably because of the short time with respect to evolution that the island has been above sea level.