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THE NATIONAL GEOGRAPHIC MAGAZINE 



NOTES ON THE EUCALYPTUS TREE 

 FROM THE U. S. FOREST SERVICE 



MORE than ico species of the euca- 

 lyptus tree have been introduced 

 into the United States. They are, how- 

 ever, adapted to a subtropical climate, 

 and only a limited portion of this country 

 is favorable for their growth. The possi- 

 bility of growing eucalyptus in any region 

 is determined by the amount of cold that 

 the young trees have to endure. Few of 

 the species can survive a temperature be- 

 low 20 ° E., and none of them a tempera- 

 ture of less than 12°. 



In general, eucalyptus may be suc- 

 cessfully planted in the sections of the 

 United States suitable for the culture of 

 citrus fruits. They are grown in nearly 

 all the agricultural sections of California, 

 along the coast of southern Oregon, and 

 to a limited extent in Arizona, New 

 Mexico, and western Texas. Several 

 species have also been planted in Florida 

 and along the Gulf coast. Here, however, 

 occasional frosts have killed or severely 

 damaged the trees, and for this reason 

 planting has been discouraged. 



The blue gum (Eucalyptus globulus) 

 has a phenomenally rapid rate of growth. 

 Seedling stands will average a height 

 growth of 50 feet in 6 years and 100 feet 

 in 10 years. Under very favorable con- 

 ditions individual trees have reached a 

 height of 125 feet and a diameter of 36 

 inches in 9 years. In sprout stands 

 growth is even more rapid ; trees fre- 

 quently reach 3 inches in diameter and 

 35 feet in height in 8 months, while in 

 3 years a diameter of 7 inches and a 

 height of 70 feet are often attained. In 

 California, under favorable conditions, 

 trees have attained a height of 175 feet 

 and a diameter of 5 feet in 25 years. Al- 

 though sometimes irregular in form, the 

 tree tends to develop a straight, grad- 

 ually tapering, unforked stem. In plan- 

 tations the trunks become rapidly cleared 

 of branches to a considerable height, but 

 in the open, trees branch more widely and 

 gradually develop a short crown of mas- 

 sive, spreading branches. 



Blue gum is practically immune from 

 disease. Where trees are reproduced by 



sprouts, the old stumps frequently decay 

 slowly at the heart, while the sprouts re- 

 main unaffected. Growing trees are not 

 attacked by insect enemies, but felled 

 timber lying unbarked upon the ground is 

 subject to injury by a wood-mining insect. 



Blue gum rarely suffers any breakage 

 of the limbs from winds, and the spread- 

 ing root system renders the trees very 

 wind-firm. 



Fire is the greatest source of injury to 

 eucalyptus plantations. Both the natural 

 characteristics of the trees and the condi- 

 tions within planted groves render them 

 peculiarly susceptible to fire injury. 

 The large quantity of litter — dry leaves, 

 branches, and shredded bark — which ac- 

 cumulates beneath a stand is extremely 

 inflammable. The bark of eucalyptus is 

 so thin that the trees are injured even by 

 light surface fires. 



The wood of blue gum is very heavy, 

 hard, strong, and tough, but it is not du- 

 rable in contact with the soil. It is close- 

 grained, and is split with difficulty after 

 it has dried. It is less elastic than 

 hickory, but it has been demonstrated by 

 mechanical tests that seasoned blue gum 

 timber is very little inferior in strength 

 and stiffness to the best second-growth 

 hickory. In appearance it closely re- 

 sembles the wood of hickory and ash. 



Blue-gum timber is utilized for a great 

 variety of purposes in California. The 

 wood is excellent for fuel, and in the 

 treeless valleys has been the chief fuel 

 supply for many years. In southern Cali- 

 fornia the steady demand renders com- 

 mercial planting for fuel very profitable. 

 Eucalyptus timber has been extensively 

 used in California for wharf piling. 

 Blue-gum piles are in use in nearly every 

 port on the California coast, and ex- 

 tended trial has shown that they resist 

 the attacks of marine borers which de- 

 stroy timber in sea water longer than 

 other species commonly used for piling. 

 Blue-gum timber has also been used to 

 some extent for fence posts and tele- 

 phone poles. The wood is not suitable 

 for this purpose, however, on account of 

 its short life in the grounl Seasoned 

 posts last a little longer than green posts, 



