For March, 1922 



79 



The Tropical Rain Forest 



WILLARD N. CLUTE 



BACK and forth across the equator moves the sun on 

 its annual journey from the tropic of Cancer to 

 the Tropic of Capricorn, carrying with it a beh of 

 rainfall that makes the so-called Torrid Zone perennially 

 green. There are. to be sure, many places in the tropics 

 where desert conditions prevail ; in fact, most of the 

 great deserts of the world lie fairly close to the equator, 

 but such regions are always caused by unusual conditions 

 such as a mountain range intercepting the moisture-bear- 

 ing winds. In other parts of the tropics the moisture is 

 not only abundant, it is superabundant. Just how abun- 

 dant it is may be realized when it is known that if all the 

 water that falls on the Eastern United States were col- 

 lected for a year, it would not equal the amount that has 

 fallen in a single day in the tropics ! In some unusually 

 wet spots there is more than six hundred inches of rain- 

 fall a year — more than fifty feet ! Under such condi- 

 tions rivers rise with great rapidity, sometimes thirty feet 

 in an hour. A body of water that behaves in this way 

 may give peculiar ideas to the natives. In Jamaica they 

 often speak of the river as a separate entity. They say 

 it is "down"' when it is running bank full and "up" when 

 it is in the clouds overhead and preparing to come 

 "down." 



The effect upon vegetation of this enormous rainfall, 

 coupled with the maximum heat and light can scarcely be 

 imagined by one who has not seen the tropical rain 

 forest. So luxuriantly do all sorts of vegetation grow- 

 that one must literally chop his way through it if he 

 leaves the beaten track. Everywhere the forest is a dim, 

 shaggy, dripping, wilderness of plants. 



One of the first differences to be noted between the 

 rain forest and the forests of temperate regions is the 

 way in which each species is scattered through the wood- 

 lands. There is seldom a grouping of single species to 

 form colonies such as we find in our forests of oak. pine, 

 beech, maple, and the like. The number of dift'erent 

 species is, of course, infinitely greater and they usually 

 attain a larger size. A new form of trees is also noticed 

 ■ — a columnar form with unbranched stem, and ample 

 leaves springing from a single bud at the summit. Of 

 this type are the various palms, tree-ferns, dracasnas and 

 numerous others. The excurrent type, represented by 

 our pines and spruces, with a central stem from which 

 smaller branches are regularly given off is usually rare. 

 Most of the forest trees, however, are of the solvent 

 type, such as is found in our elms and oaks and at a little 

 distance the tropical forest could not be distinguished 

 from a temperate region forest unless it happened to have 

 an unusual number of palms in it. 



In the desert the most interesting forms of plants have 

 been evolved by adaptations for securing and conserving 

 the scanty supply of moisture, but in the rain forest may 

 be found many devices for avoiding excess moisture. 

 Often the leaves have long slender tips for throwing 

 off the water away from the roots. With an abundant 

 and perennial supply of water and unvar>'ing warmth, a 

 new phase is given to the struggle for existence. Com- 

 petition is now for sufficient light. On the forest floor 

 are great numbers of mosses, ferns, and creepers which 

 have learned to exist in the semi-twilight cast by the 

 tall tree.s — shade plants, we call them — but plants which 

 need more light have moved to the branches of the forest 

 canopy. Thousands may be found on a single tree. 

 Among the plants with this epiphytic habit one notes a 

 large number of orchids, bromeliads, ferns, club-mosses 



and the like. Cireat lianas, or woody vines, often with 

 stems as large as a middle-sized tree, loop from tree to 

 tree and bind the vegetation into a solid mat of verdure. 



Where the forest is more open, for any cause, giant 

 herbs appear. Some of these are so large as to pass 

 for trees as in the case of the banana. This plant, how- 

 ever, as can easily be seen in the usual greenhouse, is 

 really an herb equivalent to the iris, day-lily or peony 

 of more boreal regions. Other great herbs are the gin- 

 ger, arrow-root, canna, taro, and many ferns. 



After botanizing in the tropical rain forest for a time 

 the student discovers that many of the plant families 

 which are characteristically herbaceous in regions nearer 

 the poles are here prevailingly woody. This is especially 

 true of the Lcgiiiiiiiios<r or pea family nearly all of whose 

 species are woody in the tropics. It is scarcely a sur- 

 prise, therefore, to learn that there are morning-glory 

 trees and that violets frequently grow on bushes. The 

 verbenas, the composites and even the grasses are repre- 

 sented in the tropics by species of truly tree-like propor- 

 tions. As a matter of fact, only about a dozen species 

 out of a hundred in the tropics are not woody. This, 

 however, is to be expected. In a region where every re- 

 riuirement for plant growth is abundant, the vegetation 

 naturally reaches its maximum. 



The tropical rain forest may be described as ever- 

 green, but it is not evergreen in the sense that the leaves 

 never fall. Usually the old leaves drop one at a time 

 all through the year as new ones are developed. There 

 are some species, however, even here, that take, as it 

 were, an annual vacation, throwing off their leaves and 

 standing bare for a time, even during the height of the 

 season. Most curious of all is the behavior of the tropi- 

 cal almond whose branches have not learned the ad- 

 vantage of effective teamwork and which rest, therefore, 

 as the whim seems to strike them. Such a tree presents 

 a remarkable appearance with some branches in full leaf 

 and others in complete rest. 



The visitor to the tropics, recalling the beautiful flow- 

 ers he has seen in our conservatories, expects an unusual 

 floral display but in this he is commonly disappointed. 

 There are, to be sure, occasional outbursts of bloom that 

 fairly dazzle the eye, as when the logwood is in blossom 

 or the flame tree hangs out its flowers, but seldom does 

 the tropics have anything to offer more beautiful than 

 our northern woodlands in Ma)-. Though many flowers 

 are found in the torrid zone, they are lost and their 

 beauty eclipsed by the all-pervading leafiness. Another 

 result of the mild climate is the absence of a thick bark 

 on the trees. The stems of even large specimens are 

 often a decided green. There is nothing to prevent flow- 

 ers springing from the trunk and larger branches and 

 many plants bear flowers in this way. The chocolate 

 plant is noted for producing its fruits from wood many 

 years old. In our own region practically the only woody 

 plant with this habit is the red-bud. With us, owing to 

 the progress of the seasons, each species of plant has its 

 regular time of bloom. Violets and roses bloom at one 

 end of the growing season and golden-rods, asters and_ 

 gentians at the other, but in the rain forests the plants* 

 are at no necessity of conforming to a given temperature 

 or time of year and therefore bloom whenever impelled 

 to do so. Many are in almost continuous bloom with 

 perhaps a maximum when the rainy season is at its 

 height. 



