The island of Lanai is a pear-shaped shield volcano, covering 361 km², the sixth largest of the Hawaiian Islands. At its extremes, the island is 29 km long and 21 km wide, with the highest point at Lanaihale, 1027 m (Figure 1; Armstrong 1973). Mean annual rainfall varies from 25 cm along the coast to 89 cm near the summit (Armstrong 1973), although a substantial quantity of water, estimated to be as much as the annual rainfall, is directly intercepted from the cloud cover by the vegetation in the upper mountain areas (Ekern 1964).