No abstract

A 10-year research and development program was conducted by the BioEnergy Development Corporation, USDA Forest Service, and U.S. Department of Energy on the island of Hawaii, where nearly 230,000 acres are suitable for growing biomass in short-rotation Eucalyptus plantations. Successful techniques are described for seedling production, plantation establishment (site preparation, weed control, planting), maintenance (weed control, fertilization), biomass yield estimation, and harvest. Basic biological relationships are described to aid decisions on site selection, initial spacing, fertilizer schedules, and rotation length. Environmental issues likely to be faced by growers of Eucalyptus plantations are discussed, including soil erosion, nutrient depletion, and monocultures. Continuing programs for tree improvement, monitoring, and silviculture research are recom mended. Production costs for biomass yields are estimated for three promising management regimes, representing pure Eucalyptus plantings at dense and wide spacings and a mixed species plantation where Albizia is used as a nurse crop to provide nitrogen needed for optimum Eucalyptus growth. This information will help prospective investors decide whether to invest in Eucalyptus plantations, and will help growers develop or choose among alternative management regimes.

Stand structure and crown architecture of loblolly pine (Pinustaeda L.) spacing trials in Hawaii and South Carolina were examined for attributes that would explain markedly different stockabilities (stand density per mean stand DBH), respectively, 1740 and 850 trees/ha at a quadratic mean stand DBH of 25 cm. In plots spaced at 2.4 × 2.4 m, these stockabilities produced 604 m3/ha at age 25 in Hawaii, and 297 m3/ha in South Carolina. Data collected in these stands indicate that stockability differences were associated with differences in tree size-class structure, crown length, and leaf area. Both stands were characterized by a two-tiered height structure, but the crown bases of trees in the subdominant class in Hawaii extended 1–2 m below the bases of the crowns of the dominant height class. In the South Carolina stands the crown bases of both height classes were at the same level. Green crown lengths in Hawaii were 4–7 m longer than in South Carolina, and the associated crown leaf area of 63.9 m2 was five times greater. The differences in stockability was attributed to the Hawaiian site and climate, which provide a long growing season, high solar radiation, high sun angle, favorable temperatures, and a favorable soil moisture regime and foliage nutrient status, and to a lack of significant insect and disease pests. The influence of genotype on stockability was not testable with these data.

The Authors: did the research reported herein under cooperative agreements among the Pacific Northwest forest and Range Experiment Station, Pacific Southwest forest and Range Experiment Station. and BioEnergy Development Corporation. DEAN S. DeBELL is in charge of the Pacific Northwest Station's research on the biology and silviculture offorests of the Douglas-fir region, with headq1larters in Olympia. Washington. He earned a bachelor of science degree (1963) in biology from Juniata College and master of forestry (l964) and doctoral degrees (1970) AcknOWledgments:The research reported herein was supported in part by funds of the U.S. Department of Energy's Short Rotation Woody Crops Program provided under contract to BioEnergy Development Corporation. We thank the staff of the Corporation and of the forest Service's Institute of Pacific Isla nds forestry, Honolulu, Hawaii, and the forestry Sciences Laboratory, Olympia, Washington, for assistance in field work, planning, and data analysis; the C. Brewer Analytical Laboratory for soil analyses; and the University of Hawaii Applied Research Laboratory for foliar analyses. Because of their quick growth and high yields, two Eucalyptus species are especially favored for wood, fiber, and fuel production in Hawaii. But the growth of E. saligna Sm. and E. grandis Hill ex Maid. is limited on many sites by low levels of available soil nitrogen. Supplemental nitrogen needed for sustained production of the species can be provided by application of synthetic nitrogen fertilizer or through use of N2 -fixing plants~such as legumes-or both. PublisherTo test the effects of planting leguminous trees, two species-(Acacia melanoxylon R. Bf. or Albizia falcataria (L.) Fosberg)-were added in 1: I mixtures with Euca~l'ptusin managed biomass plantations along the Hamakua coast, island of Hawaii.The experimental design consisted ofthree treatments: (I) pure Eucalyptus, (2) Eucalyptus mixed with Acacia. and (3) IIEucalyptus mixed with Albizia. The trees were planted at 2-m by 2-m spacing in August 1979, and treatments were replicated three times on plots of 0.4 ha each. Height and diameter were measured at 6-month intervals. Foliar samples of Eucalyptus were collected at 14 months after planting and analyzed for N, P, K, S, Ca, and Mg. Soil samples were obtained at 65 months and analyzed for pH, N, P, K, Ca, and Mg.At 25 months, Euca~vptus trees grown in mixture with legumes were larger than Euca~vplUs trees grown in pure plantings. At 65 months, Euca~vplUs grown in pure stands were 10.3 m tall and 8.5 cm in diameter. Euca~vptus grown with Acacia were 25 percent taller and 28 percent larger in diameter; and Euca~l'ptusgrown with A lbiziawere 63 percent taller and 55 percent larger in diameter than Eucalyptus grown in pure plantings. Despite increased mortality of Eucalyptus trees in the mixed species treatments, differences in biomass yields per ha were even greater than differences in average tree size. Crop yields averaged 38 tonnes per ha in pure Eucalyptus, 52 in EucaZvptus with A...

Plantings of Eucalyptus sa ligna (right, foreground) and Albizia falcataria (left, background) on Hamakua Coast of Hawaii Island.