KANGE AND CATTLE MANAGEMENT DURING DEOUGHT. 25 



stand in the tobosa type is not decreased nearly so much in time of 

 continued drought as in the grama-grass type. Furthermore, im- 

 provement of the tobosa type is likely to occur immediately with the 

 first wet year, while in the case of the grama-grass type several years 

 will probably be required for this recovery. The great reduction in 

 volume of forage produced in the tobosa-grass type in a dry year 

 appears to be due to a greater moisture requirement for growth than 

 in the case of the grama type species. The lesser reduction in den- 

 sity of the stand in the tobosa type in time of prolonged drought is 

 evidently due to the ability of these species to lie dormant longer 

 without moisture before dying than is grama-grass, and to a finer- 

 textured and more compact soil which has a greater air-clry moisture 

 content than the looser sandy soils of the grama-grass type. Al- 

 though tobosa-grass probably has a greater drought resistance, the 

 volume of forage produced is affected more directly by the amount 

 of moisture that falls. 



Studies of tobosa-grass areas fully grazed during summer showed 

 approximately the same depreciation on these as on areas not grazed, 

 which indicates that this type of range can be grazed fully during 

 the growing season without injury in time of drought as well as in 

 good years. The main difficulty with this type in time of drought 

 is the big decrease in foliage production rather than killing out of 

 the range, as shown in figure 6. 



VARIATION DUE TO GRAZING. 



The preceding discussion is intended to bring out the amount and 

 variation in forage production on certain- areas of the Jornada Eange 

 Reserve protected against gracing. This measure of natural pro- 

 duction indicates the maximum forage which will probably be avail- 

 able for use over a period of years under natural conditions, and is 

 a standard with which to compare production on similar ranges 

 under different grazing use so as to adjust grazing in a way which 

 will maintain the range and support the maximum stock over a period 

 of years, including drought. A comparison of this nature has been 

 made for the period 1915 to 1919, inclusive. The conditions studied 

 include ranges where grazing has been excessive yearlong for a period 

 of years, where grazing has not been too heavy for the year as a 

 whole but only during the main growing season, and where grazing 

 has been heavy for the year as a whole but much lighter than average 

 during the main growing season. A description of the areas and 

 how they were grazed, with the results and conclusions, is here pre- 

 sented. 



