Forest Trees - Bioenergy Crop Plants - page 362

Certain Eucalyptus / Albizia mixes appeared promising for maintaining Eucalyptus productivity
without fertilization. Because Eucalyptus yields in 50% and 66% Albizia mixes approached that
of fertilized pure Eucalyptus , and the Eucalyptus in mixes were so large, the mixes may be more
economical than pure Eucalyptus because of lower harvesting costs. The suggested mixed species
configuration was alternate rows spaced 3.0 m apart, with Albizia planted 2.1 m and Eucalyptus
3.0 m apart within their respective rows.
Because efficient harvesting was key to SRWC Eucalyptus feasibility, three slightly modified
conventional pulpwood harvesting systems were examined. Cable yarding did little damage to
the site or stumps but was inefficient because of inexperience and undersized and underpowered
equipment. Mechanized equipment, including wheeled and tracked feller-bunchers, a skidder, and a
whole tree chipper, handled the trees without difficulty and with relatively inexpensive but damaged
stumps. Overall, logistics as well as tree size were major determinants of productivity and cost of
harvest. Smaller, less expensive equipment might be more appropriate.
Soil erosion and nutrient depletion with SRWC Eucalyptus were minor issues. In spite of high
rainfall, pre- and postharvest soil erosion was minimal when a litter layer was developed and
retained or when a post-harvest cover crop was used (Schultz 1988). Initial total N levels were
inadequate for good growth, presumably because of intensive sugarcane cropping, mineralization
and leaching, and depletion of organic matter. N applications were substantially lower than for
sugarcane, however. N deficiency could be less when the trees are older because soil N levels after
4 years met or exceeded initial levels, Eucalyptus is very efficient at internal recycling of nutrients
(Florence 1986), or Eucalyptus / Albizia (or other N-fixer) mixes improve N levels and other soil
properties. In general, SRWC Eucalyptus impacts seem substantially smaller and less frequent than
those of agricultural crops, e.g., sugarcane.
Although superior EG and E. saligna Australian provenances were used, tree improvement would
probably increase Eucalyptus yields (Skolmen 1986). Short- and long-term improvement programs
were proposed but could not be implemented before program termination in 1988. Subsequently,
efforts by various public and private agencies have identified promising genotypes in several species.
Costs of production of the three most promising SRWC Eucalyptus alternatives were compared.
A 5-year rotation on former sugarcane land with periodic fertilization produced the minimum
acceptable 15-cm tree at a rate of 20.2 dry ton/ha per year. A 6-year rotation resulted in a 20 cm tree
with product quality advantages and a total biomass yield of 18.6 ton/ha per year. An 8-year rotation
of Eucalyptus / Albizia mix gave a larger tree size at a reduced fertilizer cost, an Eucalyptus yield of
22.4 ton/ha per year, and Eucalyptus / Albizia yield of 26.9 or more ton/ha per year. Harvesting costs
varied with tree size, decreasing by one-third as tree size doubled. Consequently, total costs per dry
ton of chipped Eucalyptus biomass were highest for the 5-year rotation and lowest for the 6-year
rotation. Overall, the information developed by the program provided valuable guidelines for future
SRWC Eucalyptus ventures in Hawaii.
About 9000 ha of Eucalyptus plantations have been established in Hawaii since 1996 (Forest
Solutions 2009). Using management procedures from around the world, these plantations are pro-
ducing over 40 m 3 /ha per year in the most productive areas.
Florida . Because of Florida's challenging climatic and edaphic conditions, much SRWC empha-
sis has been placed on Eucalyptus tree improvement for adaptability to infertile soils and damag-
ing freezes. U.S. Forest Service research from 1965 to 1984 focused on the best of 67 species for
southern Florida (Geary et al. 1983), resulting in >1500 selected EG (Meskimen et al. 1987) that
were subsequently widely tested to develop four recently released freeze resilient, fast-growing
clones. Since 1979, the University of Florida also assessed nine species, producing desirable geno-
types of E. amplifolia ( EA ) for areas of frequent freezes (Rockwood et al. 1987, 1993). EG is now
grown commercially in southern Florida for mulchwood (Aaction Mulch 2007) and can be used
in central Florida (Rockwood et al. 2008), whereas EA is suitable from central Florida into the
lower Southeast. EG is more productive, largely because of five generations of genetic improvement
(Meskimen et al. 1987).