Centuries ago Arabs discovered that the nuts growing on a certain palm tree yielded an oil that could be used in making soap, candles and greases; the ancient Egyptians used oil from the beans of the carob tree as an adhesive in the wrapping of mummies. Taking oil from trees is an idea as old as history, but today it is done by modern methods for modern purposes. Tree oils now are utilized in the manufacture of paint, food, drugs, textiles and many specialized products that people use nearly every day.
The oil palm, whose nuts were harvested by Arabs long ago, continues to be an important source of tree oil in many parts of the Middle East and even in South America. It is also an important source of income. The trees begin bearing nuts when they are about five years old and /may go on producing an annual crop of about 2,000 nuts each for as long as fifty or sixty years. Similarly the carob tree, from which the Egyptians obtained their adhesive, is still valued for its oil. Today it is grown commercially, and its oil used in the manufacture of paper, textiles and certain food products that require a "binding agent" to make them hold together.
Another ancient oil-producing tree, but one that has been grown commercially only since the 1930's, is the tung. The word comes from the Chinese for "heart-shaped," which describes its interesting leaves. Marco Polo noted the tung in the course of his thirteenth-century travels, but it was not until Americans imported it to the United States from China some 30 years ago that its oil was farmed on a large scale and used in paint, printing ink, brake lining and pressed board manufacture.
The tung is not only one of the most valuable oil trees, but also one of the most difficult to grow. A delicate tree somewhat resembling the common crab apple, it must be planted and cultivated with great care and will grow only in certain areas along the Gulf Coast. The trees require a short, cold winter, an early spring, then steadily warm summers with plenty of rain. They also require a well-drained soil, which means they must be planted on the sides and tops of hills—which are not too plentiful in the areas where the climate and soil are suitable. Once the nuts have ripened and dropped to the ground, farmers have to put them in miniature burlap bags and tie them back onto the tree for drying and aging. Only then can the nuts be finally harvested and their oil extracted. Despite the problems of growing the tung, the 200,000 acres of trees annually produce around 20,000 tons of oil. More than half of this comes from one small area in the southwest corner of Mississippi.
Two trees that produce oils with pharmaceutical qualities are the South American copiaba tree and the California sugar pine. The leaves of the copiaba yield an oil useful in treating certain kidney ailments, and the oil of the sugar pine is presently being studied as a possible rich source of vitamin B.
Common olive oil, widely used in cooking today, was known at least as far back as ancient Greece where it was an exotic luxury item used by the wealthy classes as a beauty aid.
A tree oil that is familiar to everyone but seldom thought of as an oil is turpentine, a useful solvent and ingredient in paint. The thin, highly volatile fluid is distilled from the resin of certain pine trees, and resembles white gasoline more than it does other tree oils.
Tree oil production is small compared to the 1.2 billion tons of crude petroleum pumped from the world's oil wells last year, but the oil that comes from farmers instead of drillers has numerous special uses and continues to be an important product, even as it was many centuries ago.