Deserts of America
It is often said that America has no real deserts. This is true in the
sense that there are no regions such as are found in Asia and Africa where
one can travel a hundred miles at a stretch and scarcely see a sign of
vegetation-nothing but barren gravel, graceful wavy sand dunes, hard
wind-swept clay, or still harder rock salt broken into rough blocks with
upturned edges. In the broader sense of the term, however, America has an
abundance of deserts--regions which bear a thin cover of bushy vegetation
but are too dry for agriculture without irrigation. On the north such
deserts begin in southern Canada where a dry region abounding in small
salt lakes lies at the eastern base of the Rocky Mountains. In the United
States the deserts lie almost wholly between the Sierra Nevada and the
Rocky Mountain ranges, which keep out any moisture that might come from
either the west or the east. Beginning on the north with the sagebrush
plateau of southern Washington, the desert expands to a width of seven
hundred miles in the gray, sage-covered basins of Nevada and Utah. In
southern California and Arizona the sage-brush gives place to smaller
forms like the saltbush, and the desert assumes a sterner aspect. Next
comes the cactus desert extending from Arizona far south into Mexico. One
of the notable features of the desert is the extreme heat of certain
portions. Close to the Nevada border in southern California, Death Valley,
250 feet below sea-level, is the hottest place in America. There alone
among the American regions familiar to the writer does one have that
feeling of intense, overpowering aridity which prevails so often in the
deserts of Arabia and Central Asia. Some years ago a Weather Bureau
thermometer was installed in Death Valley at Furnace Creek, where the only
flowing water in more than a hundred miles supports a depressing little
ranch. There one or two white men, helped by a few Indians, raise alfalfa,
which they sell at exorbitant prices to deluded prospectors searching for
riches which they never find. Though the terrible heat ruins the health of
the white men in a year or two, so that they have to move away, they have
succeeded in keeping a thermometer record for some years. No other
properly exposed, out-of-door thermometer in the United States, or perhaps
in the world, is so familiar with a temperature of 100º F. or more. During
the period of not quite fifteen hundred days from the spring of 1911 to
May, 1915, a maximum temperature of 100º F. or more was reached on five
hundred and forty-eight days, or more than one-third of the time. On July
10, 1913, the mercury rose to 134º F. and touched the top of the tube. How
much higher it might have gone no one can tell. That day marks the limit
of temperature yet reached in this country according to official records.
In the summer of 1914 there was one night when the thermometer dropped
only to 114º F., having been 128º F. at noon. The branches of a peppertree
whose roots had been freshly watered wilted as a flower wilts when broken
from the stalk.
East and south of Death Valley lies the most interesting section of
the American desert, the so-called succulent desert of southern Arizona
and northern Mexico. There in greatest profusion grow the cacti, perhaps
the latest and most highly specialized of all the great families of
plants. There occur such strange scenes as the "forests" of suhuaros,
whose giant columns have already been described. Their beautiful crowns of
large white flowers produce a fruit which is one of the mainstays of the
Papagos and other Indians of the regions. In this same region the yucca is
highly developed, and its tall stalks of white or greenish flowers make
the desert appear like a flower garden. In fact this whole desert, thanks
to light rains in summer as well as winter, appears extraordinarily green
and prosperous. Its fair appearance has deceived many a poor settler who
has vainly tried to cultivate it.
Farther south the deserts of America are largely confined to
plateaus like those of Mexico and Peru or to basins sheltered on all sides
from rain-bearing winds. In such basins the suddenness of the transition
from one type of vegetation to another is astonishing. In Guatemala, for
instance, the coast is bordered by thick jungle which quickly gives place
to magnificent rain forest a few miles inland. This continues two or three
score miles from the coast until a point is reached where mountains begin
to obstruct the rain-bearing trade-winds. At once the rain forest gives
place to jungle; in a few miles jungle in its turn is replaced by scrub;
and shortly the scrub degenerates to mere desert bush. Then in another
fifty miles one rises to the main plateau passing once more through scrub.
This time the scrub gives place to grass-lands diversified by deciduous
trees and pines which give the country a distinctly temperate aspect. On
such plateaus the chief civilization of the tropical Latin-American
countries now centers. In the past, however, the plateaus were far
surpassed by the Maya lowlands of Yucatan and Guatemala.
We believe deserts are places where the plants are of few kinds and
not much crowded. As a matter of fact, an ordinary desert supports a much
greater variety of plants than does either a forest or a prairie. The
reason is simple. Every desert contains wet spots near springs or in
swamps. Such places abound with all sorts of water-loving plants. The
deserts also contain a few valleys where the larger streams keep the
ground moist at all seasons. In such places the variety of trees is as
great as in many forests. Moreover almost all deserts have short periods
of abundant moisture.
At such times the seeds of all sorts of little annual plants,
including grasses, daisies, lupines, and a host of others, sprout quickly,
and give rise to a carpet of vegetation as varied and beautiful as that of
the prairie. Thus the desert has not only its own peculiar bushes and
succulents but many of the products of vegetation in swamps, grasslands,
and forests. Though much of the ground is bare in the desert, the plants
are actually crowded together as closely as possible. The showers of such
regions are usually so brief that they merely wet the surface. At a depth
of a foot or more the soil of many deserts never becomes moist from year's
end to year's end. It is useless for plants to send their roots deep down
under such circumstances, for they might not reach water for a hundred
feet. Their only recourse is to spread horizontally. The farther they
spread, the more water they can absorb after the scanty showers. Hence the
plants of the desert throttle one another by extending their roots
horizontally, just as those of the forest kill one another by springing
rapidly upward and shutting out the light.
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