National Geographic : 1908 Oct
CORK CORK is the outer layer of bark of an evergreen species of oak. The tree is cultivated principally in Portugal and Spain. When the tree is about 15 or 17 years old the first stripping takes place, but this first crop is too coarse in texture to be of use except in tanneries or for rough purposes. The second stripping, obtained 8 or Io years later, is also too coarse for finer uses than for floats for nets. With each stripping the quality improves and is continued at in tervals of 8 years until the tree is 150 years old. During the last several years the French have begun to exploit the natural cork of Algeria, where they have found about I,ooo,ooo acres occupied by the cork oak. The largest forests are in northeastern Algeria and contain some trees with a circumference of more than 30 feet. Messrs Thomas H. Kearney and Thomas H. Means, of the U. S. De partment of Agriculture, give the follow ing description of the cork oak industry: Only natural forests are exploited in Algeria, no attempt ever having been made to establish artificial plantations (as in Spain and Portugal). In bringing a forest of cork oak into condition for exploitation the first step is to remove the layer of old or "male" cork which forms under natural condi tions. This operation, which requires considerable skill, is performed in the spring when the sap is beginning to rise. The subsequent yield depends largely upon the way in which this work of "demas clage" is done. It is advisable to put back into place the layer thus removed, fastening it around the trunk by means of wire and leaving it there for about two years; otherwise the trees are very liable to injury from dry, hot winds and from fire. Wrapping the trees in this way also prevents a second development of the worthless male cork. The new cork which now begins to form is alone of commercial value. It is deposited at the rate of from 0.04 to 0.12 inch annually, and the first harvest is taken when the layer of cork has reached a thickness of about I inch. Thereafter the cork is removed every eight or ten years, the later crops yielding a better product than the earlier ones. The ex pense of each harvest from a single tree is about 2 cents. Individual trees differ greatly in the rate at which cork is formed. As a rule, the best product is that which develops most slowly. Rapidly growing cork is more abundantly veined with loose tissue,. which diminishes its value. The cork is sometimes seriously injured on the tree by the ravages of ants, which build gal leries in it. The tree has also other insect enemies. The cork, when cut, rolls up into tubes of the size of the trunk from which it was taken. It is first pressed out into. sheets, then boiled, and finally the crust of bark is removed by scraping. Boiling increases the bulk by about one-fifth and renders the cork more elastic. An acre of cork oak in full production yields a net annual revenue of about $2. The product from a single tree is worth from 4 to io cents a year after all ex penses are deducted.