Eucalyptus spp. are successful SRWCs because of their fast growth and environmental tolerance due to attributes such as indeterminate growth, coppicing, lignotubers, drought/fire/insect resistance, and/or tolerance of soil acidity and low fertility, and many have desirable wood properties for bioenergy production. They have been domesticated for various products and have been widely commercialized in the tropics and subtropics. Significant plantings of Eucalyptus in the United States began with introductions from Australia as a result of the California Gold Rush in 1849. Eucalyptus species were introduced in the southern USA as early as 1878, but no significant commercial plantations were established until the late 1960s (Dougherty and Wright, 2012; Stanturf et al., 2013). Eucalypts are grown extensively as exotic plantation species in tropical and subtropical regions throughout Africa, South America, Asia, and Australia, and, in more temperate regions of Europe, South America, North America, and Australia (Stanturf et al.,2013).
Biology and Production System
While there are more than 700 species, less than 15 species are commercially significant worldwide (Gonzalez et al., 2011). Seed introductions of Eucalyptus species in the United States were focused primarily in Florida (Zon and Briscoe 1911) due to climatic similarities with Australia. Eucalyptus prefer moderately well drained soils with some degree of clay content for water retention.
Planting and Production
Eucalyptus production practices in different parts of the world vary with site conditions, desired products, and scale of commercialization. Genetic selection has led to commercialization of genotypes with unique advantages in different applications. They are commercially propagated by both seed and cloning of tissue culture. For conventional pulpwood production, stands are typically established at a planting density of 1,482 to 2,471 trees ha-1, and harvested every 6-10 years. They may be replanted at harvest, which can benefit from improved genetic material, or regenerated from coppice growth, which eliminates the cost of replanting.
Because of high growth rates and tolerance to a range of growing conditions, Eucalyptus can be produced in innovative ways, providing non-market benefits. It can be used for restoration of phosphate-mined lands (Rockwood and Carter, 2006; Langholtz et al., 2007; 2009) and has been shown to be effective at phytoremediation of reclaimed wastewater, municipal waste, storm water, and arsenic-and trichloroethylene-contaminated sites (Rockwood et al., 2008; Langholtz et al., 2005).
Breeding and Genetic Improvements
Most domesticated eucalypts are from the subgenus Symphyomyrtus, the largest of the 10 subgenera currently recognized within Eucalyptus (Rockwood et al., 2008). E. grandis is the most widely used species in plantation forestry worldwide in tropical and subtropical areas not only as a pure species, but also as a parental species in hybrid breeding. It has the fastest growth and widest adaptability of all Eucalyptus species.
Eucalyptus species are ideal for genetic improvement because many typically propagate easily, have short generation intervals and broad genetic variability, and may be genetically engineered. Research on genetic improvement of Eucalyptus in the US has been put emphasis on tree improvement for adaptability to infertile, soils and damaging freezes. Through a significant advance in the understanding of freezing tolerance in Arabidopsis, a freeze-tolerant Eucalyptus has been developed (Yamaguchi-Shinozaki and Shinozaki, 1993). A renewed effort to identify frost-tolerant species and genetic modifications to increase frost-tolerance that will permit expansion of the range of Eucalyptus is driven by potential need for 20 million Mg yr-1 of Eucalyptus wood for pulp and biofuel production in the southern US by 2022 (Rockwood et al., 2008). Genetic improvement programs aim to improve varieties for various growing conditions.
Eucalyptus yields are influenced by precipitation, fertility, soil, location, genetics, and management practices. In the southern US, rotation length and yields for biomass for bioenergy can be 3-4 years with a 12.3 to 22.4 Mg (oven dry) ha-1 y-1 (Gonzalez et al., 2011). Eucalyptus spp. yielded 18 to 35 Mg (oven dry) ha-1 annually after 3-5 years of growth on clayey soil in central Florida, comparable to 21 to 34 Mg (oven dry) ha-1 yr-1 estimated for Eucalyptus in Australia (Pereira et al., 1989). This hybrid is also predicted to produce 34 to 43 green Mg ha-1 yr-1 on a seven year rotation in traditional pulpwood management system and 43 to 52 green Mg ha-1 yr-1 in biomass management system. On the other hand, Eucalyptus saligna Smith in 5 and 6-year rotations and an 8-year Eucalyptus/Albizia mix produced 20.2, 18.6, and 26.9 or more Mg (oven dry) ha-1 yr-1, respectively (Whitesell et al., 1992). Biomass production of Eucalyptus in Brazil (Hall et al, 1993), Spain (San Miguel, 1988), and Hawaii (San Miguel, 1988) were within this range (Table 1).
Mg (oven dry) ha-1
Mg (oven dry) ha-1
|San Miguel, 1988|
|35||12-22||Worldwide||Gonzalez et al., 2011|
|9-26||Mid Brazil||Hall et al., 1993|
|58||40-50||India||Prasad et al., 2010|
|27||13-27||Hawaii||Whitesell et al., 1992|
|30||20-24||Australia||Pereira et al., 1989|
|2.9||Ethiopia||Selamyihun et al., 2005|
|28||3-21||NE Brazil||Carpentieri et al., 1993|