VEGETATION DECLINE FOLLOWING RECENT ERUPTIONS ON WHITE-ISLAND (WHAKAARI), BAY-OF-PLENTY, NEW-ZEALAND

Vegetation decline following recent (1976-90) eruptions on White Islan d (Whakaari) was assessed during 1986 and 1990 using historical accoun ts (1959 and 1967) as a baseline. More than two-thirds of the Metrosid eros excelsa (pohutukawa) forest and scrub and all of the gannetry veg etation had declined markedly and several species had become locally e xtinct. The most probable causes of death of M. excelsa were toxic fum es, wet ash coating leaves, and ''acid rain''. For the small herbaceou s species, complete burial by tephra was probably the main cause of de ath. Size class structures of three forest plots and M. excelsa growth ring counts suggested several phases of forest development, with the most advanced forest older than 180 years. Data from M. excelsa forest s on other volcanic islands indicate that mature M. excelsa forest dev elops in 250 years. The depauperate flora of White Island compared wit h other Bay of Plenty islands probably results from the extreme soil c onditions and continuing volcanicity. With the current eruption regime on White Island, further vegetation decline is expected.