Evening star., 1936-06-29
VESTS SDROUGHTS
OCCUR IN CYCLES.
Three Regular Periods of
Varying Duration Cited
in Report.
BY THOMAS r. HENRY.


For 5000 years the Western United
States has been squeezed in the coils
Of two or three interlocking and un-
predictable drought cycles.
There is a short period cycle run
ming from three to seven years, a
longer one running from 80 to so
years and a still longer one run
ming from 100 to $50 years.
Sometimes all three cycles reach
their peaks togeths-and this may
be what is happening now as the
northern intermountain area faces
what may be. some experts fear, the
worst drought in its history.
During the past so years, records
just compiled by the Range Re
search Division of the United States
Forest Service show, there have been
six notable drought periods-l8SS to
1890, 1898 to 1904, 1910, 1917, 1919,
1924 and 1928 to 1884, inclusive.
These have been interspersed with
years Of relatively plentiful rain.
Tree Rings Indicate Past.
The record can be carried back as
far as 1910 B. c. by means of tree
ring eXaminationS-a method which
during the last four or five years has
been brouhgt to such perfection that
in certain areas the precise year when
@ ring was formed can be determined.
Trees add new ring of wood each
year and the width of each ring cor
responds to the precipitation available
that year.
Tree ring studies in Arizona, as re-
ported by the Forest Service. show
dry years recurring in IA and 81 year
cycles with major droughts every $50
years and minor droughts at 40 or
so year intervals. Periods Of poor
growth in the Pacific Northwest be-
tween 1880 and 1880 recurred at inter-
walls of from to IA years. There are
no records for the region now eSpe-
cially affected but there Is every
reason to believe that it fits into the
general picture.
One must plan for less than average
four years out of every ten. warns r.
S. Campbell. senior forest ecologist of
the Forest Service If this were all
there would be no particular reason
to worry, since the Great Plains and
intermountain vegetation has re-
markable adaptability to such condi-
tions. Within single year it can
recover almost completely from the
effects of such drought.
The plants of the range country
have an inherent drought wisdom. the
Forest Service report explains Their
physiological mechanism has been per-
fected by evolution to make the most
Use of available water
Fluctuations Growth Are Large.
Fluctuations in growth and abund-
ance are enormous. For example,
large areas in Montana are covered by
a species known as Wheat-graSS For
est Service measurements show that in
1888 the average height of stalks of
this grass was 13 inches. During the
great drought of 1884 1t fell to an
average OF l inch. Then, showing its
remarkable recuperative powers, the
average height last Summer was Is
inches. But this Is deceptive, the
Forest Service specialist points out.
The stockmen who looked forward
with confidence to complete recovery
failed to take into consideration the
density of the new growth. This de-
chnes progressively. 1t may continue
to decline. even in a wet year follow
ing dry one. An experimental stand
Of mixed perennial grasses in South
ern Idaho varied from 969 square
centimeters of coverage in 1925 to
269 square centimeters in 1885.
The range country could stand
such extreme fluctuations of vegeta-
tion coverage under natural condi-
tions, but when over-grazed by sheep
and cattle the recuperative power is
lost. Without any human interfer-
ence, the Forest Service expert says
the vegetation fluctuations of the area
are as definite and specific as the tree
ting fluctuations.
For any definite year there is no
means of prediction. The present
drought area may have drenching
rains tomorrow. However, this is i'm
probable since droughts tend to be
progressive. The less moisture there is
In the soil and streams, the less water
there is to make rain. The one thing
certain is that there will be periods
within every decade of less than aver
age rainfall, that there will be periods
within every half century when
drought will become extreme, and that
over periods of centuries there will be
killing droughts.
At present the cumulative precipi-
tation in this region is slightly less
than was the case at the same time