1906| SHANTZ—VEGETATION OF THE MESA 203 
scene practically that which follows on a denuded area. Salvia line- 
aris, Atriplex argentea, and Bouteloua prostrata are here the principal 
species. With these are found many of the ruderal plants as well as 
ah following important perennials: A gropyron occidentale, Astragalus 
bisulcatus , Sophora sericea, Vicia americana, and a very little Bouteloua 
oligostachya, Quincula lobata, and Phyllopterus montanus. 
The effect is to delay the succession or to cause it to return to a 
more primitive condition. The grazing does not change the Boute- 
loua formation into another formation, since grasses seem to be 
especially adapted to these conditions. 
he effect of grazing is very different on the thicket formation. - 
Wherever cattle are allowed to crop the thicket formation very closely, 
the facies are completely killed. This is the most noticeable in the 
ci aa oaks, which are killed by the entire loss of chlorenchyma 
oe attacked by cattle before any of the other facies 
of the thicket formation. 
oo Honat the region shows that on the mesa near Colorado 
the ar a formation has been replaced almost entirely by 
parvifolia sy tenes Only scattered bushes of Cercocarpus 
a ee sia sptaaaa are found and these much reduced in 
SE a aes lies in the fact that this portion has been 
City. >The ro an the part which is farther removed from Colorado 
aiid the ans lacie of the old thicket can be seen in many places, 
nee Sp m : le succession which have produced a grass forma- 
plant growth . : icket formation may be traced. There is a scanty 
ne, > er these shrubs. When they are killed outright 
come in in - vas plant invasion, and as a result the ruderals 
Sli st ance. Chenopodium album may be one of the 
destroyed oop ae at this time, especially if the cattle have 
the shrubs have be e under vegetation. At other places where 
Same as the tear ising down the succession may be much the 
formation. As a ; . uccession and result in the typical Bouteloua 
The result here is ne e the shrubs are gradually reduced in size. 
the shrubs are eat = the grasses slowly encroach upon the area as 
the: derek is ower, and as the clump becomes more open 
S. neo-mexicana, A - Saree: Agropyron occidentale, Stipa comata, 
, Atheropogon curtipendulus come in slowly; Coleo- 
