236 THE FUTURE OF ARID LANDS 
year to the next, but periods of continuous excess or deficiency 
may persist for 4 or § years. Grazing management systems must 
be designed to meet the large changes in forage production that 
result from variations in rainfall (8, 11). 
Stocking Based on Below-Average Forage Production 
The wide variation in rainfall and the consequent variability in 
annual forage production makes proper stocking essential. At- 
tempts to adjust stocking each year to the highly variable amount 
of forage, unless properly done, may have disastrous results. A 
breeding herd built up to use the forage crop produced in good 
years cannot be maintained in subsequent dry years. The practical 
way to utilize the highly variable forage crop is to stock conserv- 
atively. 
A margin for safety is proy.ded by stocking at a level less than 
that which the average forage production will support. Ungrazed 
forage produced in favorable years provides a forage reserve for 
lean years and also protects the soil. In southern New Mexico, 
stocking at 65% of average forage production is recommended 
for black grama (Bouteloua eriopoda (Torr.) Torr.) and tobosa 
grass (Hilaria mutica (Buckl.) Benth.) ranges (g). Even at this 
seemingly conservative rate of stocking, severe reductions of live- 
stock numbers would be needed during prolonged periods of 
drought such as have occurred three times during the last four 
decades. Obviously, the desirable levels of stocking will vary widely 
with climatic regions and forage species, but stocking somewhat 
below the average forage crop should be practiced on arid ranges. 
Moreover, the basic breeding herd should be kept low—s5 to 
60% of the total number grazed. The remainder of the herd 
should be made up of younger, more salable animals that can be 
disposed of quickly when dry periods and short forage supplies 
occur. This practice will safeguard the most valuable breeding 
herds (3). 
Seasonal Grazing for More Forage 
Yearlong grazing is the most punishing form of use. If contin- 
ued, this practice reduces the proportion of desirable forage species 
and the amount of usable forage; it will also result in thinning of 
