Eucalyptus: Taxonomy, Geographic Distribution, Domestication, Breeding, Ecology and Economic Importance

Eucalyptus are widely cultivated for supplying raw material to industries, and other uses like shade, shelter and fuel. Eucalyptus occur naturally in Australia and adjoining regions of Papua New Guinea, Indonesia and the Philippines. The cultivated species belong to the subgenus Symphyomyrtus in the genus Eucalyptus. Eucalypts are generally outcrossed with large natural diversity in growth and adaptive traits, which may however change with domestication in introduced populations. Breeding programmes use native germplasm and improved seed lots to increase productivity and maintain genetic diversity. Interspecific hybrids have increased the productivity substantially by exploiting hybrid vigour. Clonal forestry is widely used to enhance wood productivity, but breeding programmes are necessary for long-term sustainability. Gall wasp emerged recently as a major pest seriously affecting many eucalypt species. Eucalyptus resorts to luxury consumption of water, but they are also more water-efficient than some native trees. The seed-origin root system includes shallow lateral roots in the upper soil layers, a vertical tap root in early growth stages and vertically growing sinker roots in later stages. Plantation sites significantly impact wood traits, which can be rapidly assessed using near infrared spectroscopy. This chapter deals with the natural distribution, genetic diversity, improvement and ecology of eucalypts. Economic and industrial relevance of the important species is also discussed.