INCREASING PRODUCTION WITHOUT ACCELERATING EROSION 243 
fall soil moisture deficit on areas where soils are deep and less 
water would be required to prime the soils before runoff 
occurred (17). 
As a general rule, the more arid the climate the less the oppor- 
tunity to increase water yield by thinning or removing vegetation. 
With the exception of plants growing along watercourses, the 
water used by vegetation comes from soil moisture that can be 
removed from the soil only by plant roots or by evaporation. In 
dry climates, this moisture is lost from the soil with or without 
plants. Changes in vegetation are expected to provide more water 
where precipitation is mainly in the form of snow, or where it falls 
in large enough quantities to saturate the soil at frequent 
intervals (7). 
Growing Demands; Limited Resources 
Demands upon arid lands in the southwestern United States 
have increased and will continue to increase. Recently, there has 
been a decline of subsistence farming and ranching and a tre- 
mendous growth of urban populations. The concentration of popu- 
lation increases the strain on water resources because no one 
locality has sufficient water naturally available to it to support its 
present size and future hopes. Water is no doubt a resource that 
will continue to be limiting. Managers of forest and range lands 
have an obligation to protect water supplies. Fortunately, prac- 
tices that maintain and improve forage and forest production are 
also beneficial in controlling erosion and reducing sedimentation. 
A first need on much of our watershed lands in the arid Southwest 
is repair and rehabilitation. Past damage has been severe, but de- 
terioration need not continue. Improvement has already been 
made in many areas. Human needs and demands can be expected 
to fluctuate and vary from one product to another in the course 
of time. We must safeguard all arid land resources so that future 
needs can be satisfied. 
REFERENCES 
1. Anderson, Darwin, Louis P. Hamilton, Hudson G. Reynolds, and 
Robert R. Humphrey. 1953. Reseeding desert grassland ranges in 
southern Arizona. Ariz. Agr. Expt. Sta. Bull. 240. 
