RANGE MANAGEMENT IN NEW MEXICO. 23 



UNDESIRABLE RANGE PLANTS. 



Besides the useless shrubs occurring on the gravelly mesas, two 

 other types of undesirable plants occur. These may be called for 

 convenience range weeds and poisonous plants. Range weeds are 

 of two kinds — native and introduced — and their presence upon the 

 range is due to two facts : First, and of much the greater importance, 

 because the animals will not eat these plants at all or only when 

 forced to do so by extreme hunger; and, second, because their natural 

 plant dominants (both biologic and economic) have been removed 

 by overstocking. 



In the main, those native plants which have become the commonest 

 and apparently most important range weeds are not very aggressive 

 and would not occupy the large areas they do but for the effective 

 assistance in their struggle for existence which they receive from the 

 animals. Yet so important has this factor of animal interference 

 with the adjustment of plants in different associations become that 

 large areas are often occupied by almost pure stands of plants that 

 would normally form but an insignificant part of the vegetable 

 covering. 



The best example of this kind of a range weed is found in the snake- 

 weed (Gutierrezia spp.), which also is called by its Mexican name 

 yerba del vibora (PI. VI, fig. 1) . In many places it is called sheep weed 

 because of its abundance on overstocked sheep ranges. So infrequent 

 is this plant on a normal range which has not been overstocked that 

 the average observer rarely sees it, and it has often been sent to the 

 writer as an example of a recently introduced and very harmful weed. 



In response to the oft-repeated question of how to get rid of the 

 snakeweed, there is but one method economically possible, and that 

 is to give the grama grass a chance and it will crowd out the snake- 

 weed. In the eastern counties of the State, where the influx of 

 settlers several years ago drove range stock out and gave much of 

 what had been range land a long and much-needed rest, this very 

 thing happened. It usually happens inside the fences of the railroad 

 rights of way. There is little doubt also that the burning of the 

 dead grass, a custom of the Indian days, was very destructive to the 

 snakeweed, which is quite resinous, burns readily, and is easily killed 

 by fire, but it did little damage to the grass except to destroy the 

 standing dry crop. Advantage might be taken of this fact locally 

 to hasten the eradication of this weed. Rabbit brush (ChrysotTbam- 

 nus spp.) occasionally assumes this rdle in certain localities. 



Another common, though less important, weed of the open parks 

 in the forests is the .Rocky Mountain bee plant, which in places 

 occupies large areas to the more or less complete exclusion of some 

 of the best of the forage plants. (PL VI, fig. 2.) 



