An altitudinal transect analysis of the windward vegetation on Haleakala, a Hawaiian island mountain: (1) c1imate and soils
Kitayama, K.; Mueller-Dombois, D.
Climate and soils were studied to classify habitat types along an altitudinal transect between 350 m asl and the summit on a windward slope of Haleakala (3055 m) There are two relatively sharp turnover points in atmospheric moisture regime: the lower and upper cloud limits. Although they fluctuate along the slope, the lower and upper limits occur, in the summer, most frequently at c. 1000 m asl (corresponding to the lifting condensation level) and c. 1900 m asl (the base of the trade wind inversion), respectively. The two limits result in three broad altitudinal climatic zones: the atmospherically moist lowland ( 1900 m asl). The lowland is characterized by diurnally regular, modest desiccation; the montane by diurnally and yearly perhumid air; and the high altitude by diurnally irregular, severe desiccation and by a yearly extensive summer drought. The high altitude zone is subdivided into three subzones: the frost-free zone (1900-2400 m asl), the ground-frost zone during winter (> 2700 m asl), and the ecotone zone in between. There are two broad edaphic zones with a boundary coinciding with the most frequent inversion base at 1900 m asl. The soils below this altitude are wet, those above are arid. The soil in the lowland interfluve is the most reduced and poorly drained, despite its moderately dry atmosphere. This reduction seems to be related to poor lateral drainage due to its flat topography, and to the addition of water by downslope run-on. The soils, thus, tend to become better drained with increasing altitude. Physical and chemical properties of the soils change upslope in association with the change in soil water regime.