VEGETATION OF BRAZOS CANYON 187 



too great a tendency among makers of life zone maps to show 

 the lower zones extending up into the upper ones along the 

 streams. In New Mexico this is true in a general way of the 

 large streams. In the great valley of the Rio Grande, for 

 instance, taking the valley as a whole and not merely the flood 

 plain of the river, the Lower Sonoran vegetation extends far to 

 the northward. Along small streams, like the Chama and 

 Brazos, just the reverse is true in a region of low rainfall like 

 New Mexico. Here, under the favorable conditions of mois- 

 ture, as well as temperature (although this latter is not readily 

 apparent but is easily accounted for) , the vegetation of the higher 

 zones is carried far down into the lower ones and should be shown 

 on a map as tongues extending down, not as recessions. This 

 is probably not true in a humid region, but it certainly is the 

 case in New Mexico. 



Typical Transition Zone 



The one tree here is the yellow pine (Pinus brachyptera) , 

 except along the creeks, where the mountain cottonwood (Popu- 

 lus angustifolia) replaces it. The stand of pine about the Brazos 

 Canyon and Tierra Amarilla is nowhere heavy, but this is 

 doubtless the result of lumbering, for, farther west, on the 

 Jicarilla Apache Reservation, under similar conditions, the 

 stand is equal to any in the State. 



The vegetation of this division of the Transition Zone is very 

 uniform, except along the streams and on the rock slides, be- 

 cause the conditions of moisture, soil, and exposure are every- 

 where similar. On the rock slides few trees can find a foothold, 

 but there are many shrubs, chiefly A melanchier sp.,Padus melano- 

 carpa, Grossularia leptantha, and Sericotheca dumosa. A few 

 scattered shrubs of Juniperus scopulorum were seen on the 

 rocks, probably introduced by birds. Some of the herbaceous 

 plants noticed as common are Pericome caudata, Coleosanthus 

 grandiflorus, Eupatorium fendleri, Chrysopis villosa, and Cap- 

 noides aureum, these mingling with others that are properly 

 Canadian. The banks of the Brazos are lined with mountain 

 cottonwoods, which extend up as far as the mouth of the canyon. 



