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 em ip 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 (Chrysotham- 
nus spp.) occasionally assumes this réle 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.) 
