BANGE MANAGEMENT IN NEW MEXICO. 25 



Whatever may be said of the undesirability of weeds on a range, 

 there is one thing to be said in their favor. Any vegetable covering 

 in an arid region is better than none, since such a covering prevents 

 to some degree the removal of the soil, and any plant association 

 occupying an area is to be looked upon as merely one stage in the 

 production of that ultimate assemblage of plants which is best 

 adapted to that place and its conditions. 



EROSION. 



To the observer from a humid climate, perhaps no one charac- 

 teristic of the arid regions of the Southwest is so startling as the evi- 

 dence on all sides of the forceful action of water as an erosive agent. 

 And this in a land where water is the one thing that is everywhere 

 lacking. 



But the reason is patent after a summer in the region, and the 

 conditions are common to all arid countries of high relief. The ero- 

 sive effects that one sees so plainly are the resultant of several factors. 

 During the warm weather, the only season of the year in which large 

 volumes of moist air are brought into the region, the air next the 

 ground is always warm and therefore relatively dry. Hence, rain 

 occurs only when masses of humid air are forced into the cold upper 

 strata. Such conditions arise only locally and produce showers of 

 restricted size, but such showers are mostly torrential in character, 

 a large amount of water falling on a restricted area in a very short 

 time. 



Let such a downpour occur on what seems to be a flat plain, and 

 in a few minutes the lower levels are flooded and the roadbed of any 

 obstructing railroad is apt to suffer severely. Thus, we are forever 

 hearing of railroad washouts in a region that is called a desert and 

 is wanting governmental irrigation systems established. (PI. VIII, 

 fig. 2.) 



The land is but sparsely covered with any kind of vegetation and 

 there is little to obstruct the run-off. The gradient is high at almost 

 any place. Add to this the fact that the soil has been loosened by 

 daily expansion and nightly contraction, due to large diurnal varia- 

 tions of temperature, and the conditions for maximum efficiency of 

 the erosive agent are supplied; and the consequences are not only 

 not singular but were to be expected instead of wondered at. 



The factor which more than anything else tends to prevent the 

 same kind of results in a humid region on an even larger scale is the 

 protective cover of vegetation everywhere abundant, and no one fac- 

 tor is so efficacious in producing rapid erosion on the arid grazing 

 lands as the more or less complete removal of their already scanty 

 cover of plants by overstocking. 



