34 BULLETIN 1031, U. S. DEPARTMENT OF AGRICULTURE. 
and September, but grazing at that time does not seem to affect 
tobosa-grass range, so that the latter should be used for summer ~ 
range and the former at other times. Should grama-grass range be 
overgrazed this fact may be detected by the various plant species 
that come in on the range and steps should be taken to reduce graz- 
ing and protect the range during the growing season. 
GRAZING CAPACITY. 
The effect of drought and time of grazing upon the grazing capac- 
ity of the range is of prime importance in working out a plan of 
management to secure maximum maintained cattle production on 
southwestern ranges. The summary given in the last few pages 
shows that there is a great reduction in amount of forage produced 
per unit of area due to drought and considerable variation due to 
difference in the time and extent to which the grama-grass range 
is grazed. The data show also that the reduction increases with 
each year of drought. Should the first few years following drought 
be favorable an increase in forage production toward the maximum 
will undoubtedly occur. To determine approximately what these 
changes mean in number of stock or percentage of stock, from year 
to year throughout a cycle including a drought and the good years 
following, is a problem that must be solved if similar conditions are 
to be prepared for in advance and the “ downs” of cattle production 
on ranges of the Southwest be reduced or eliminated. 
By grazing capacity 1s meant amount of grazing that may be se- 
cured per unit area. Usually this amount is expressed, however, in 
acreage per head of stock on any given range for the period the range 
is used. On most of the southern New Mexico ranges the stock are 
grazed yearlong. Grazing capacity is therefore expressed in terms 
of acres per head for the yearlong period, or, in other words, acreage 
required to furnish a year’s grazing for one animal, although graz- 
ing may be hghter than average during part of the year. 
True grazing capacity obviously is the acreage of a given range 
required to support one animal of a given class over a period of years 
without injury to the range. This ideal is difficult to attain on any 
range and is especially so on ranges of southern New Mexico, which 
are subject to the changes and variable factors briefly discussed in 
preceding pages. It is hoped, however, by caretul records and 
adjustments over a period of years to approach the ideal closely 
enough to avoid unwarranted waste of forage through nonuse and 
certainly to avoid the serious overstocking common in the past. ln- 
provement in grade of stock and comparatively higher prices for 
better stock in thrifty condition will aid in approaching the ideal 
by making it profitable to insure proper care of the stock through 
