Productivity, nutrient and water-use efficiency of Eucalyptus saligna and Toona ciliata in Hawaii

We studied changes in productivity and resource use of the Australian hardwoods Eucalyptus saligna and Toona ciliata along a gradient in elevation (650-1300 m) and rainfall (annual mean from 2600 to 1200 mm per year) in the island of Hawaii. The stands were on either organic or volcanic ash soils developed on 1200-2400, and 13,000 year-old lava flows, respectively. Leaf area index (LAI) of E. saligna decreased, and leaf carbon isotope composition (delta C-13) and specific leaf weight (SLW) increased with increasing elevation, suggesting structural (changes in stand leaf area), physiological (increased water use efficiency throughout stomatal closure) and leaf morphological adjustments to reduced water availability. The relatively high net primary aboveground productivity of E. saligna on young organic soils (15.8-23.7 Mg ha(-1) per year) was possibly explained by high nitrogen productivity (NP=467 kg kg(-1) per year in average). Stands of E. saligna both on shallow volcanic ash on smooth (pahoehoe) lava flows and on wet organic soils at low elevations had evidence of windfall episodes that reduced standing basal area up to 35%. Stand or leaf characteristics of T. ciliata did not significantly change along the gradient. Average N content per unit leaf weight in T ciliata was higher than that for E. saligna, but N contents per unit leaf area were similar for both species. Productivity and NP of T. ciliata were about one half than those for E. saligna with higher productivity of T. ciliata on volcanic ash soils compared to organic soils. While E. saligna adjusted both structurally and physiologically along the gradient, growth and physiological changes of T. ciliata were less obvious. Several hardwoods grown in Hawaii uplands had different growth and physiological responses to environmental changes. (C) 2000 Elsevier Science B.V. All rights reserved.