RANGE IMPROVEMENT. 325 



population, as in mountain meadows with high rainfall, or in wet valleys with 

 littlfe drainage, tame grasses or forage plants can be introduced into the com- 

 munity successfully and without disturbing it unduly. Such areas constitute 

 a relatively small amount of the total range, and they are rarely in such need 

 of revegetation as the grasslands of low water-content. In deaUng with the 

 latter, the first great need is to take advantage of times of greater rainfall. 

 This has generally been done with reference to the season, but no method has 

 heretofore been available for anticipating periods of several years with rain- 

 fall above the normal. Such a method now exists in the use of the sun-spot 

 cycle to determine the probable duration of the wet and dry phases of the 10 

 to 12-year climatic cycle. While the annual rainfall varies more or less dur- 

 ing the wet phase, it is regularly higher than during the dry one. Moreover, 

 drought periods of 2 to 3 years' duration have been found to fall only at the dry 

 phase for the past 60 years. Hence, it is obvious that the difficulties attendant 

 upon reseeding or introduction will be least during the wet phase and greatest 

 during the dry one, and that all operations of this kind should be confined to 

 the former. Moreover, it is especially desirable that sowing or transplanting 

 be repeated for the first two years of the wet period in order that an adequate 

 stand be secured in the event of the seasonal distribution of the rain being 

 unsatisfactory. This would also accord with the probabiUty of two or three 

 fairly wet years for the proper establishment of the plants, before the begin- 

 ning of the dry period. 



A second prerequisite of great importance is the eradication of rodents. 

 Where seeding is the method used, it is probable that the failure to secure a 

 good stand is often due as much to the destruction of the seeds as to the lack 

 of water. This is probably true even in the arid Southwest, since it is here 

 that rodent damage is greatest. As a consequence, it is imperative to kill out 

 the rodent population before seeding operations are begun on an area. It is 

 almost as important to make sure that the rodents are kept out of such areas, 

 since they may turn the scale against the establishment of plants which have 

 germinated successfully. The food habits of the kangaroo-rat help to explain 

 why the grama grasses fail to make seed and gradually disappear in the experi- 

 ments mentioned above. In certain regions, at least, they would Ukewise 

 render the establishment of transplants much more difficult. It is also 

 obvious that areas in which reseeding is being carried on must be protected 

 against grazing for several years. As a consequence, reseeding and trans- 

 planting should be fitted into the rotation system, and carried on with refer- 

 ence to the period of complete or partial rest given the different areas. It is 

 assumed that all such operations must still be regarded as actual investigations 

 and that they will be begun only where fencing assures control, and a pre- 

 liminary study of conditions presupposes some degree of success. Under such 

 conditions, it is possible to take the factor of competition into account also. 

 The success attained in artificially reseeding bare and especially trampled 

 areas in pastures has been largely due to the absence of competition for water. 

 When reseeding is employed to increase the density of an existing com- 

 munity or to introduce new dominants, competition becomes a critical factor. 

 It can be adequately modified only in small pastures where disking or harrow- 

 ing is economically desirable, or irrigation possible. On the ranges of the 

 Southwest, with two growing seasons, it can be avoided by the use of winter 

 annuals, which do not come into direct competition with the summer grasses 

 at all. 



