Bryophytes and Lichens of the Puhimau Geothermal Area, Hawaii Volcanoes National Park

Abstract

The vegetation of the Puhimau geothermal area was compared with that of the surrounding ecosystem. Very few species of the surrounding area were found with any abundance in the geothermal area. The center of the geothermal area is almost barren. Pockets of vegetation dominated by the endemic moss Campylopus praemorsus (C. Muell.) Jaeg. are throughout the central area. The only other temperature-tolerant species present is Portulaca sclerocarpa Gray. Cladonia oceanica Vain. is commonly found growing epiphytically on the moss away from the high temperatures. The central zone is surrounded by an Andropogon-dominated grassland in which both C. praemorsus and C. oceanica are commonly fertile. No lichens exhibited any tolerance of high temperatures. The Puhimau geothermal area, often referred to locally as the Puhimau Hot Spot, is located on the east rift zone of Kilauea volcano on the island of Hawaii. The area was formed in the winter of 1937-38 when magma came close to the surface and resulted in hydrothermal activity rather than the usual destruction associated with lava flows. The original Metrosideros forest was killed but not burned. The steam vents formed were confined principally to the bases of tree trunks. Some of these trunks are still present in the area and support a distinctive fumarolic community. Although sulphurous gases are normally emitted from fumaroles during the degassing of subterranean lava, no sulphur dioxide or hydrogen sulphide gas has been recorded from the vents in the Puhimau thermal area in recent years (Siegel & Siegel 1979). Recent subterranean volcanic activity in the area resulted in a short (less than 48 hours) emission of SO2. Fosberg and Lamoureux (1966) briefly described the vegetation of two areas of the east rift zone of Kilauea in Hawaii Volcanoes National Park in which there was hydrothermal activity. One of these areas has since been destroyed in the formation of Mauna Ulu. In these areas, they recorded Cladonia cf. cristatella (= C. oceanica Vain.), C. cf. rangi- ferina (= C. skottsbergii Magn.), and Racomitrium (presumably R. lanuginosum var. pruinosum Wils.). Kappen (1973), citing a personal communication from Mueller-Dom- bois, confirmed the presence of these lichens scattered on volcanic soils. Ground tem- peratures from 48 to 89?C have been recorded in both areas, suggesting that all species growing there were remarkably heat tolerant. Although lichens (Lange 1953; Kappen 1973) and mosses (Noerr 1974) are very tolerant of high temperatures when desiccated, when hydrated their tolerance is significantly di- minished. Some mosses are tolerant of temperatures up to 50'C (Noerr 1974) whereas lichens can remain active only up to about 25-30?C (Lange 1965).