Plantations of Eucalpytus saligna Sm. grow rapidly in Hawaii, but supplemental nitrogen (N) is required on many sites. Because of the high cost of synthetic N fertilizer, mixed species plantings in which N is added by Albizia falcataria (L.) Fosb., an N2-fixing tree, are being tested on the island of Hawaii. Five combinations of Eucalyptus and Albizia were compared with each other, with pure Albizia, and with pure Eucalyptus fertilized periodically with nitrogen. The test is a randomized block design with four replications on the wet, Hamakua coast. At 48 months, Eucalyptus trees in the mixed plantings containing 34% or more Albizia were equal to or larger than those in the pure, fertilized stands. Total dry yields ranged from 109 ton/ha in pure Albizia plantings to 67 ton/ha in mixed species plantings with only 11% Albizia. Yields in the mixed plantings with 34 to 66% Albizia were 103 to 105 ton/ha, whereas yield in the pure, fertilized Eucalyptus stand was 94 ton/ha. Nitrogen concentration of Eucalyptus foliage increased as the amount of Albizia increased in the stand; and in mixed plantings with 34% or more Albizia, foliar N concentration exceeded that of the pure, fertilized, Eucalyptus treatment. Phosphorus levels in Eucalyptus foliage similarly increased as amounts of Albizia increased in the stand. At 48 months, total N was higher in soils of mixed species and pure Albizia plantings than in soils of the pure, fertilized Eucalyptus treatment. Albizia can provide the N needed by Eucalyptus in high-yielding bioenergy plantations along the Hamakua coast. For. Sci. 35(1):64-75.
Silviculturist, Pacific Northwest Forest and Range Experiment Station, Olympia, WA, Pacific Southwest Forest and Range Experiment Station, Honolulu, Hawaii, USDA Forest Service, BioEnergy Development Corporation, Hilo, Hawaii