Rain Forests of America
In their relation to human life the forests of America differ far more
than do either grass-lands or
deserts. In the far north, as we have
seen, the pine forests furnish one of the least favorable environments. In
middle latitudes the deciduous forests go to the opposite extreme and
furnish the most highly favored of the homes of man. Still farther
southward the increasing luxuriance of the forests, especially along the
Atlantic coast, renders them less and less favorable to mankind. In
southern Mexico and Yucatan the stately equatorial rain forest, the most
exuberant of all types of vegetation and the most unconquerable by man,
makes its appearance. It forms a discontinuous belt along the wet east
coast and on the lower slopes of the mountains from southern Yucatan to
Venezuela. Then it is interrupted by the grasslands of the Orinoco, but
revives again in still greater magnificence in the Guianas. Thence it
stretches not only along the coast but far into the little known interior
of the Great Amazon basin, while southward it borders all the coast as far
as southern Brazil. In the Amazon basin it reaches its highest development
and becomes the crowning glory of the vegetable world, the most baffling
obstacle to human progress.
Except in its evil effects on man, the equatorial rain forest is the
antithesis of the forests of the extreme north. The equatorial trees are
hardwood giants, broad leaved, bright flowered, and often fruit-bearing.
The northern trees are softwood dwarfs, needle-leaved, flowerless, and
cone-bearing. The equatorial trees are often branchless for one hundred
feet, but spread at the top into a broad overarching canopy which shuts
out the sun perpetually. The northern trees form sharp little pyramids
with low, widely spreading branches at the base and only short twigs at
the top. In the equatorial forests there is almost no underbrush. The
animals, such as monkeys, snakes, parrots, and brilliant insects, live
chiefly in the lofty treetops. In the northern forests there is almost
nothing except underbrush, and the foxes, rabbits, weasels, ptarmigans,
and mosquitoes live close to the ground in the shelter of the branches.
Both forests are alike, however, in being practically uninhabited by man.
Each is peopled only by primitive nomadic hunters who stand at the very
bottom in the scale of civilization.
Aside from the rain forest there are two other types in tropical
countries--jungle and scrub. The distinction between rain forest, jungle,
and scrub is due to the amount and the season of rainfall. An
understanding of this distinction not only explains many things in the
present condition of Latin America but also in the history of
pre-Columbian Central America. Forests, as we have seen, require that the
ground be moist throughout practically the whole of the season that is
warm enough for growth. Since the warm season lasts throughout the year
within the tropics, dense forests composed of uniformly large trees
corresponding to our oaks, maples, and beeches will not thrive unless the
ground is wet most of the time. Of course there may be no rain for a few
weeks, but there must be no long and regularly recurrent periods of
drought. Smaller trees and such species as the cocoanut palm are much less
exacting and will flourish even if there is a dry period of several
months. Still smaller, bushy species will thrive even when the rainfall
lasts only two or three months. Hence where the rainy season lasts most of
the year, rain forest prevails; where the rainy and dry seasons do not
differ greatly in length, tropical jungle is the dominant growth; and
where the rainy season is short and the dry season long, the jungle
degenerates into scrub or bush.
The relation of scrub, jungle, and rain forest is well illustrated
in Yucatan, where the ancient Mayas reared their stately temples. On the
northern coast the annual rainfall is only ten or fifteen inches and is
concentrated largely in our summer months. There the country is covered
with scrubby bushes six to ten feet high. These are beautifully green
during the rainy season from June to October, but later in the year lose
almost all their leaves. The landscape would be much like that of a thick,
bushy pasture in the United States at the same season, were it not that in
the late winter and early spring some of the bushes bear brilliant red,
yellow, or white flowers. As one goes inland from the north coast of
Yucatan the rainfall increases. The bushes become taller and denser, trees
twenty feet high become numerous, and many rise thirty or forty feet or
even higher. This is the jungle. Its smaller portions suggest a second
growth of timber in the deciduous forests of the United States fifteen or
twenty years after the cutting of the original forest, but here there is
much more evidence of rapid growth. A few species of bushes and trees may
remain green throughout the year, but during the dry season most of the
jungle plants lose their leaves, at least in part.
With every mile that one advances into the more rainy interior, the
jungle becomes greener and fresher, the density of the lower growths
increases, and the proportion of large trees becomes greater until finally
jungle gives place to genuine forest. There many of the trees remain green
throughout the year. They rise to heights of fifty or sixty feet even on
the borders of their province, and at the top form a canopy so thick that
the ground is shady most of the time. Even in the drier part of the year
when some of the leaves have fallen, the rays of the sun scarcely reach
the ground until nine or ten o'clock in the morning. Even at high noon the
sunlight straggles through only in small patches. Long, sinuous lianas,
often queerly braided, hang down from the trees; epiphytes and various
parasitic growths add their strange green and red to the complex variety
of vegetation. Young palms grow up almost in a day and block a trail which
was hewn out with much labor only a few months before. Wherever the death
of old trees forms an opening, a thousand seedlings begin a fierce race to
reach the light. Everywhere the dominant note is intensely vigorous life,
rapid growth, and quick decay.
In their effect on man, the three forms of tropical forest are very
different. In the genuine rain forest agriculture is almost impossible.
Men finds himself baffled in the face of Nature. Many things combine to
produce this result. Chief among them are malaria and other tropical
diseases. When a few miles of railroad were being built through a strip of
tropical forest along the coast of eastern Guatemala, it was impossible to
keep the laborers more than twenty days at a time; indeed, unless they
were sent away at the end of three weeks, they were almost sure to be
stricken with virulent malarial fevers from which many died. An equally
potent enemy of agriculture is the vegetation itself. Imagine the
difficulty of cultivating a garden in a place where the weeds grow all the
time and where many of them reach a height of ten or twenty feet in a
single year. Nowhere in the world is there such steady, damp heat as in
these shadowy, windless depths far below the lofty tops of the rain
forest. Nowhere is there greater disinclination to work than among the
people who dwell in this region. Consequently in the vast rain forests of
the Amazon basin and in similar small forests as far north as Central
America, there are today practically no inhabitants except a mere handful
of the poorest in the world. Yet in ancient times the northern border of
the rain forest was the seat of America's most advanced civilization. More
on that later.
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