Introduction

High elevation shrublands occur above the tradewind inversion (c. 2000 m), on the geologically young (< 1 000 000 years old) volcanoes of Maui (Haleakala volcano) and Hawaiian (Mauna Kea, Mauna Loa and Hualalai volcanoes). Except for Mauna Loa, which recently erupted at the 3000 m level in 1984, these volcanoes are quiescent. Vegetation of the high elevation Hawaiian volcanoes consists of shrubs (Styphelia, Coprosma, Vaccinium, Dubautia, Dodonaea, Geranium), small trees (Sophora, Myoporum, Santalum), perennial graminoids (Deschampsia, Agrostis, Trisetum, Luzula, Carex), and other perennial herbaceous species (Pteridium aquilinum, Asplenium, Silene, Sanicula, etc.). With increasingly severe climatic conditions at higher elevations and with proximity to a mountain's summit, vegetation becomes more sparse and smaller in stature. Vegetation at the uppermost limit consists of prostrate shrubs, grasses, and ferns (Hartt & Neal 1940; Fosberg 1959; Mueller-Dombois & Krajina 1968; Whiteaker 1983). The fresh lava substrates of Mauna Loa (elevation 4170 m) result in much less development of soil and vegetation there than on older Mauna Kea (4207 m) and Haleakala (3056 m), both of which have extensive outcrops of cinder and ash deposits (Fosberg 1959). Hualalai Volcano (2522 m) barely reaches into the high elevation zone.

Mean temperature in the Hawaiian Islands decreases upward on the volcanoes at a rate of about 0.53 °C per 100 m.