1906] SHANTZ—VEGETATION OF THE MESA 201 
The most important plant occupying the alluvium deposited by 
permanent streams is Melilotus alba. Species of minor importance 
are Juncus bujonius and Riccia crystallina. 
ANOMALOUS SUCCESSION. 
When biotic or physical agencies bring about sufficient change 
in the habitat, the result is an anomalous succession. The change 
of habitat may be gradual and yet the effect on the succession be 
such as will change entirely the ultimate formation. We may also 
have the succession interfered with in such a way as to hasten the 
ultimate formation, to cause it to become more stable in a shorter 
time, or to retard the succession or reduce it to a more primitive 
condition. 
Due to grazing. 
The influence of grazing is very clearly seen by comparing fenced 
areas with those that have not been protected from grazing animals. 
Cattle, and to a less extent horses, are the only animals that have 
grazed within this region in recent years. 
Near the lower end of the mesa is Colorado City, the old territorial 
capital of Colorado and known as one of the oldest towns in the state. 
For fifty years it has been the custom to have a herd boy drive the 
cattle out on the adjacent areas to graze each day and bring them 
back each night. Colorado Springs, a more recent city, also sends 
its herds out on the same area. It will be well, at first, to see what 
effect this has had upon the Bouteloua formation. In those parts of | 
the formation where grazing has not played a part the formation is 
very open, while in the grazed portions it is more closed. In the 
open formations many species appear with the grasses, while in 
the more closed formation these species are almost entirely absent. 
A typical quadrat from the south mesa which has been grazed shows 
the following species: 
Muhlenbe 
tgia gracillima . 23 33% Sideranthus spinulosus 3 
Bouteloua oligostachya. . 24 12 Wi Weeut rack ‘concuieues 5 
“ropegon curtipendulus 1 Townsendia exscapa . . 2 
a GS 2 Echinocereus viridiflorus . I 
Boebera Papposa. . . 36 
Total surface covered, 45 to 50%. 
