The Encyclopedia Americana (1920)/Forest Trees, Tropical
FOREST TREES, Tropical. Most interesting trees grow between the tropics, some of which have traveled quite around the globe. A vast number of economic products, exclusive of the more important tropical fruits, derived from them, have been carried far and wide since the dawn of commerce. The character of these forests varies greatly, influenced by waterfall and altitude. This is illustrated in Porto Rico where “the various formations in the order of their occurrence from the coast toward the interior are as follows: Littoral woodlands, moist deciduous forests, and tropical rainforests on the north or humid side, and the dry deciduous forest on the south or semi-arid side.” These different formations overlap more or less, or disappear but are to be recognized everywhere in the tropics.
The most obvious difference lies between those trees growing on hot dry areas like the Liguanea plain in Jamaica, where rain falls perhaps twice a year and then in torrents, and those forming dense forests on the nearby mountains, where rain and fogs are frequent. In dry soil the trees grow sparsely, and are apt to be low and broad of head, with foliage subdivided, and sometimes armed with thorns. The leguminous tribe is usually well represented. In the jungle, however, the arborescent growth is more interesting to the eye. The foliage is often evergreen, thick and glossy with waxen coatings designed to shed water, and simple of outline. In the heat and moisture of these damp deciduous and tropical rain forests, as Colonel Roosevelt remarks, “The struggle for life among the forest trees and plants is far more intense than in the North. The trees stand close together, tall and straight, and most of them without branches, until a great height has been reached; for they are all striving toward the sun, and to reach it they must devote all their energies to producing a stem which will thrust its crown of leaves out of the gloom below into the riotous sunlight which bathes the billowy green upper plane of the forest.” The trunks of these trees are usually pale gray or pallid in hue, and many of them have brilliant flowers such as those crowning the bois immortelle, which are, however, unsuspected by the stroller beneath, unless the forest floor be littered with gay petals fallen from their place under the sun, where only an aeronaut or mountain climber can see them. Huge vines or lianes, which rise upward with the trees that they embrace, are characteristic of these forests; some are as straight and thick as saplings, others are twisted and contorted; others cling inseparably to the boles. Some clothe the tree-trunks with verdure, others hang naked like ropes dangling from a ship's rigging. The trees are moreover loaded with masses of epiphytic plants, ferns and mosses. Orchids form huge tufts, or trail in long flowering streamers, and stiff wild pines hold water in the cup-like bases of their leaves in which little batrachians bathe. These features are most easily seen at the edges of clearings laboriously hacked out with cutlass or machete for garden patches. Tropical forests are continuously destroyed and steep hills left bare for the action of erosive forces, by these small cultivators who supply most of the constant supply of green-stuff used in towns. They cut down the giant trees with all their burdens and either consume them in charcoal kilns or in huge bonfires that are a characteristic sight among the mountains, burning like beacons night and day, and often burning over more territory than is required. The ashes supply fertilizer, and when the ground is exhausted in a few years the gardeners repeat the process.
As in the north, certain tropical trees are notable. Such are the banyan (Ficus Bengalensis), an individual tree soon becoming an umbrageous grove by sending down roots from its branches, and its near relative, the sacred bo-tree, or peepul (Ficus religiosa) in whose ever-quivering foliage dwell Indian gods. Sometimes eccentric growth, like those swollen trunks of bottle trees (Sterculia) of Australia, makes them noticeable or some peculiar usage, as when the easily-hollowed trunks of baobabs (Adansonia digitata), are utilized for cisterns for storing water caught in near-by tanks during the rainy season — an adaptation of great service during the recent campaigns in Africa. Often it is the flowers that attract, as is the case of the flaming Spathodea Nilotica, or of the royal poinciana (Poinciana regia). The succulent, golden corollas of the Indian mahwa (Bassia latifolia), falling profusely, bring the peasantry in crowds to feast on the fleshy petals, that sometimes save them from starvation, and to distil from them a nauseous intoxicating liquor. The sacred and fragrant asoka (Saraca Indica) and champaca (Michelia Champaca), on account of their flowers are planted about Eastern temples for ceremonial use. The delightfully-scented flowers of the latter are used as a cheap drug and are also the source of a perfume said to be substituted for that of the more valuable ylang-ylang (Cananga odorata), a huge tree of the Philippines, whose tassel-like flowers retain their odor even when dried and were hawked about the streets of Manila in trays for sachets. The fluffy, yellow flower-balls of several acacias, more particularly those of the aromo, huisache, cassie or popinac as the Acacia Farnesiana is variously denominated, are similarly plucked for their odor. Likewise, nearly the whole of the citrus tribe contribute essences for perfumers' uses, as does also the Eucalyptus citriodora, and that very large South American tree, Dipteryx odorata, whose fruits — tonka beans — were formerly scented snuff. Balsams of Peru and of Tolu (Myroxylon) and other fragrant gums and resins extracted from tropical trees, as well as the odorous heartwood of lign aloes (Aquilaria) and sandalwood (Santalum), find their way into perfumery.
Pungent camphor is distilled from the wood of Camphora officinalis and many other drugs are taken from tropical trees, sometimes from the fruit, as from the cylindrical pods of the golden flowered Cassia fistula, or from those red and white nuts of Kola, which are so greatly sought by Africans that they pass from hand to hand as currency; or from the bark, as in the case of Cinchona, so long jealously guarded by its Andean discoverers; of the West Indian quassia (Picraena excelsa), a substitute for the Oriental Quassia amara; or the Jamaica dogwood (Piscidia erythrina); or of the winter's bark (Drimys Winteri).
Saponaceous materials are obtained from soap bark (Quillaia) and from the soapberry (Sapindus). Cocum butter is extracted from the seeds of Garcinia Indica; shea butter, used for food and illumination along the Niger, from the nuts of Bassia, a genus that is rich in oil-yielding species. Candlenuts (Aleurites moluccana) are so oily that they were formerly strung on grasses in Hawaii and burned as candles. The cohune palm (Attalea Cohune) and the African oil palm (Elæis Guineensis), among others, yield commercial oils, and wax is shaken or scraped from those two palms Copernicia and Ceroxylon. Ben oil, a favorite with perfumers, comes from the horseradish tree (Moringa).
Even the juices of tropical trees are utilized. South America boasts of the cow-tree (Galactrodendron utile), from which when gashed flows a quantity of thick white fluid, cream-like in consistency, and bearing a slight astringency in taste. The naseberry (Achras Sapota) secretes “chicle” gum, and a number of different trees furnish that milky sap which hardens into rubber or guttapercha. The pigment gamboge is derived from the yellowish sap of Garcinia Morella.
An orange red dye, used for coloring dairy products, is obtained from the arils of annatto or achiote seeds (Bixa orellana); but more important dye-stuffs are the heartwood of fustic (Chlorophora tinctoria) tinting yellow; of Brazilwood (Cæsalpinia Brasiliensis) dyeing red, and of the graceful logwood (Hæmatoxylon Campechianum) yielding fine blues and blacks. Logwood flowers profusely, and bees make one of the finest kinds of honey from the fragrant blossoms.
Cabinet woods are another commercial product of the tropics that is very valuable. Sandalwood, camphorwood and cedar (Cedrela odorata) are favorite materials for clothes-chests and boxes, since the aromatic and fragrant woods repel insects. Cabinet makers went to the East for their hard sable ebony (Diospyros ebeneum), for the blackwood (Dalbergia) so much used by the Chinese, for teak (Tectona grandis) for carving, and for the shimmering satinwood (Chloroxylon Swietenia); but South America and the West Indies have their satinwoods (Fagara and Simaruba), and also an ebony (Brya ebenum), besides rosewood and the peerless mahogany (Swietenia mahogoni) which seekers discover by climbing other trees to locate the mahogany by its delicately-cut pale foliage, among other methods. They also have the ale-brown wavy-grained yacca (Podocarpus), a conifer, and the mountain mahoe (Hibiscus elatus) vividly striped with green and white. In the Philippines the yellow or reddish heartwood of molave (Vitex), narra (Pterocarpus), tindalo (Pahudia rhomboidea) and the dark-brown walnut-like acle (Pithecolobium acle) are valued for furniture and cabinet making.
The wealth of the tropics in timber trees is scarcely realized or drawn upon. Some of the trees are so hard and heavy that carriage from their site is prohibited, even if their habitat were not often in utterly inaccessible locations; and if they could be fetched away they would be too difficult to work with profit, or too limited in usefulness. On the other hand some tropical woods are surprisingly soft and light. The Lauan group of the Philippines may be compared to soft pine, being used for light construction and furniture. Ochroma, or balsa-wood (Ochroma lagopus) of the West Indies is so buoyant that it is used as a substitute for cork, and is said to be the lightest wood in the world; its relative, the silk cotton or ceiba (Ceiba pentandra), a huge tree regarded by negroes with much respect if not worshipfully, is not much heavier. Its enormous boles, braced by those sinuous narrow-walled, buttressing roots that are so characteristic of many gigantic tropical trees, dominate open glades in the forest. They have been hollowed out for dug-out canoes by the natives, who made paddles, from the thin walls of the buttresses. The “floss” or “silk,” a soft fibrous material surrounding the seeds, is more important than the timber, being used as an upholstery material called “Kapok,” and as a moisture-defying, weightless padding for soldiers' bedding in the trenches. It resembles the red silk-cotton of the Eastern “Simal” (Bombax Malabaricum) of the same family.
Among the heavy woods, teak (Tectona grandis), second only to mahogany in value, is famous for its durability in tropical climates. When properly seasoned — in Burma, the tree is girdled and left standing dead on the stump for years, — it can be floated out of the forests. It is also partially resistant to insect attacks and those of teredos which is a very important property in the tropics, and is mainly used for shipbuilding and for carving, as are also the bibiri (Nectandra rodioei) or greenheart, which is the chief article of export from British Guiana, which is insect and teredo proof and is therefore especially useful for under-water construction.
Trincomali wood (Berria Ammomila) and Sal (Shorea robusta) are valuable Oriental trees for general construction, and timber from various species of gums (Eucalypti) and Kauri (Dammara Australis), which include some of the tallest trees of the world, are invaluable to Australasia. The ubiquitous tamarind (Tamarindus Indica) offers another useful wood, and in the countries about the Caribbean we find the small but exceedingly hard lignum-vitæ (Guaiacum officinale) famous for its wearing qualities, the locust (Hymenæa Courbaril), the yokewood (Catalpa longissima) of very general usefulness; the ausubo (Sideroxylon fœtiddissima); the candlewood, or tabanuco (Dacryodes excelsa); the lance wood (Oxandra lanceolata) very elastic and exported for shafts and fishing rods; the crab-wood (Carapa guienensis); the tropical cedar (Cedrela odorata) made up into cigar boxes; and a host of other trees. The Philippines produce the ipil (Intsia), particularly durable when cut for ties; betis (Illipe betis), and the aranga (Homalium) and liusin (Parinarium griffithianum) valuable for salt-water construction as in wharfs.
Bamboos attaining to the height of trees, although really enormous grasses, have an infinite variety of uses ranging from food to house construction and surround the globe. The curious mangrove swamps that lie on sheltered shores are equally common throughout the tropics, and are raided for fuel, pilings, and, in the Far East, for tanbarks and dyes. Other tannins are obtained from the twisted pods of divi-divi (Cæsalpinia coriaria), and from Australian wattles, especially from the golden wattle (Acacia pycnantha) and the black wattle (A. decurrens), the latter being cultivated also in Hawaii. Cutch is a product of A. Catechu. Acacias, moreover, yield fine and durable wood, sometimes fragrant, and many commercial gums, as gum arabic. The kair tree (A. Catechu) of India is there considered to be even more durable than teak, and to be uninjured by insects, while A. Koa of Hawaii is said to be the best timber in that territory.
A common tree on tropical shores is the yellow-flowered tulip-tree, or emajaguilla (Thespesia populnea) which is a favorite shade, timber and ship-building tree in India. Its bark yields a strong fibre for tying bundles. It belongs to the mallow family famous for its fibres, which also includes the emajagua or mountain mahoe (Hibiscus elatus) that furnishes a fibre compared to jute, used for cordage and also for millinery. Its inner bark was stripped for tying cigars and was known as “Cuba bast.” An extraordinary form of these netted bast fibres exists in the lace-bark-tree (Lagetta lintearia) which can be pulled into open meshes much resembling a coarse white fabric. A white cloth is manufactured in Africa from Uganda bark-cloth trees (Brachystegia). The mulberry family is also redundant in bark fibres, clothing and sacks being evolved from the bark of the upas tree (Antiaris toxicaria), while the finest and whitest cloth and mantles worn by Hawaiians were made from the beaten bark of Broussonetia papyrifera, also famous as a paper-stock. Similar lacy bark layers are found in the Australian flame tree (Sterculia acerifolia) and other species of this genus; and in nettle-trees (Laportea; Trema) of both Australia and India.
The leaves of screw-pines (Pandanus utilis) are plaited into coarse sacks, and the fibres otherwise employed, but the greatest source of basket material in the tropics and of fibre for innumerable purposes lies in the palm family, which is probably the most useful as well as picturesque of any in the equatorial zone. The foliage of the round-leaved species, when properly trimmed, becomes fans; others are torn into strips such as raffia, from Raphia, which are woven into hats, baskets and the like. The huge leaves of many serve as thatch for the slight tropical buildings. The stringy fibre of other species, like that of Mauritia flexuosa; of the tecuma palm (Astrocaryum tucuma); or that known as piassaba fibre derived from the extraordinary Leopoldinia piassaba and from Attalea funifera and still other species, is twisted into cordage or made into brooms and brushes. Kittool fibre comes from the jaggery palm (Caryota urens); and coir, woven into cocoa-matting and said to make the finest cables on account of its elasticity, lightness and durability under water, comes from the fibrous husks of the coconut (Cocos nucifera).
The dried kernel of the coconut palm is called copra and is one of the chief articles of export from the Philippines and other archipelagos of the Southern Seas, an important commercial oil being extracted from the desiccated flesh. Before the kernel has hardened at all the soft green husk is filled with a clear fluid, as pure and tasteless as water, which is the safest and most refreshing drink of the tropics. The husk is slashed with a heavy knife and the native pours the fluid down his throat directly from the nut. Oil is yielded by the fruits or nuts of other species, especially from those of the Cohune palm (Attalea Cohune), and from the more important African oil palm (Elæis Guinensis), yellow and violet scented, extensively exported for soap and candles. The small nuts of a stemless palm (Phytelephas macrocarpa) have white kernels that become so hard that they are used instead of ivory, the tree therefore being called ivorynut palm. Areca Catechu furnishes those fruits known as betel-nuts, chewed by Orientals with a bit of lime and betel pepper.
The twin nuts of the coco-de-mer (Lodoicea callipyge) found floating on the ocean, caused endless speculation among mariners who concluded that they were borne on a submarine palm, before the great trees were discovered in the Seychelles. Other palm fruits are the well-known dates from the cultivated Phoenix dactylifera, so important a food and article of export from Africa; those of several American species are sought for by the natives, especially the small bitter fruits of the mucuja (Acrocomia lasiospatha), and of the peach-palm (Guilielma speciosa). A favorite Brazilian drink was extracted from the macerated thin pulp of the tiny fruits of the graceful assai (Euterpe oleraceæ).
Not a few beverages, intoxicating or otherwise, are concocted from palm sap. In the Philippines, the fresh or mildly fermented sap drawn from the inflorescence of the coconut and nipa palm is called “Tuba”; wine and alcohol are made from the sap of the latter (Nipa fruticans). Filipinos also make wine, syrup and sugar from the burri, or talipot palm (Corypha umbraculifera), commercial sago furthermore being obtained from its soft pith. The chief source of that article, however, is Sagus. (The so-called sago palms (Cycas) are really members of the cycad family). A similar starchy food, and copious quantities of sap are produced by the East Indian wine palm (Caryota uren) the latter known as toddy, being a pleasant drink while fresh, but soon fermenting. When boiled it yields jaggery sugar and when distilled, the beverage called arrack. Like products are obtained from the sugar palm (Arenga saccharifera) and other species. The wine palm of Africa is the jupati (Raphia vinifera).
Camauba wax is shaken from the encrusted foliage of the wax palm of Brazil (Copernicia cerifera) sometimes used to adulterate beeswax; and another vegetable wax is scraped from the trunks of Ceroxylon Andicola of New Granada, where it is mixed with vegetable tallow for candles. Several palms are robbed of their terminal buds, so that they may be cooked as vegetables; hence they are called cabbage palms. One, the tall West Indian palm (Oreodoxa oleracæa), is a relative of the magnificent royal palm (Oreodoxa regia).
Bibliography.— Cook, O. F., and Collins, G. N., ‘Economic Plants of Porto Rico’ (Contrib. United States Nat. Herb. Vol. VIII, pt. 2, Washington 1903); Fawcett, W., ‘Guide to the Botanic Gardens, Castleton, Jamaica’ (Kingston, Jamaica, Hope Gardens 1904); id., ‘Index to Economic Products of the Vegetable Kingdom in Jamaica’ (Jamaica 1891); Gifford, J. C., ‘Luouillo Forest Reserve, Porto Rico’ (United States Department Agriculture, Bureau of Forestry Bulletin 54, Washington 1905); Harris, W., ‘Timbers of Jamaica’ (Imp. Department of Agriculture for West Indies, Reprint from West Indies Bulletin, Vol. IX, No. 4, pp. 297-328, 1909); Murphy, L. S., ‘Forests of Porto Rico’ (United States Department of Agriculture Bulletin 354, Washington 1916); Philippine Commission Report, pt. 3 (United States War Department, Vol. IX, Washington 1907); Shinn, C. H., ‘Economic Study of Acacias’ (United States Department Agriculture Bulletin 9, ib. 1913); Smith, J. G., ‘Black Wattle in Hawaii’ (Hawaii Agricultural Experiment Station Bulletin 11, ib. 1906); ‘Useful Fibre Plants of the World,’ and many pamphlets issued by the United States Agricultural Department.