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 hardw oods Eucalyptus saligna and Toona ciliata along a gradient in elevation (65 0-1300 m) and rainfall (annual mean from 2600 to 1200 mm per year) in the i sland of Hawaii. The stands were on either organic or volcanic ash soils de veloped on 1200-2400, and 13,000 year-old lava flows, respectively. Leaf ar ea index (LAI) of E. saligna decreased, and leaf carbon isotope composition (delta C-13) and specific leaf weight (SLW) increased with increasing elev ation, suggesting structural (changes in stand leaf area), physiological (i ncreased water use efficiency throughout stomatal closure) and leaf morphol ogical adjustments to reduced water availability. The relatively high net p rimary aboveground productivity of E. saligna on young organic soils (15.8- 23.7 Mg ha(-1) per year) was possibly explained by high nitrogen productivi ty (NP=467 kg kg(-1) per year in average). Stands of E. saligna both on sha llow volcanic ash on smooth (pahoehoe) lava flows and on wet organic soils at low elevations had evidence of windfall episodes that reduced standing b asal area up to 35%. Stand or leaf characteristics of T. ciliata did not si gnificantly change along the gradient. Average N content per unit leaf weig ht in T ciliata was higher than that for E. saligna, but N contents per uni t leaf area were similar for both species. Productivity and NP of T. ciliat a 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. salig na adjusted both structurally and physiologically along the gradient, growt h and physiological changes of T. ciliata were less obvious. Several hardwo ods grown in Hawaii uplands had different growth and physiological response s to environmental changes. (C) 2000 Elsevier Science B.V. All rights reser ved.