PLANT SUCCESSION AND EANGE MANAGEMENT. 29 



tention of the water supply in the upper layer of the soil in seasons 

 of less than normal rainfall often causes somewhat serious desicca- 

 tion in the lower soil layer, upon which yellow brush is largely de- 

 pendent for water, and results in the death of many of these plants. 

 Obviously, however, the desiccation of the lower soil layer is most 

 serious immediately beneath the dense bunches of porcupine grass. 

 As a result of the seed of porcupine grass finding ready lodgment 

 and conditions especially favorable for germination immediately be- 

 neath the expanded branches of yellow brush, dense tufts of porcu- 

 pine grass, as shown in figure 9, often develop around the yellow- 

 brush plants. The established yellow-brush plant is killed in a season 

 or two or possibly straggles along for a few seasons. Where the 

 competition is not too severe some of the branches of the yellow 

 brush die and most of the branchlets on the remaining branches are 

 killed, thus greatly reducing the leaf surface as well as the loss of 

 water from transpiration. This reduction in the leaf surfacje often 

 permits yellow brush to hold its place with the porcupine grass for 

 a considerable time. Naturally under such conditions yellow brush 

 produces few flowers and practically no viable seed, so that physio- 

 logically its behavior is much the same as a plant that has been seri- 

 ously weakened as a result of too frequent cropping. 



PALATABILITY. 



With its large variety of palatable plants and its relatively small 

 percentage of waste range, the porcupine-grass-yellow-brush conso- 

 ciation probably furnishes as ideal a vegetative cover for all classes 

 of grazing animals as the lands are capable of producing. Small 

 mountain porcupine grass, of which the foliage is finer leaved and 

 less harsh than that of the wheat grasses, is grazed with relish by all 

 classes of stock throughout the foraging season. While vigorous 

 growth ceases in most habitats during the first half of August, the 

 herbage remains more or less green until well into September. When 

 cured, the leafage of small mountain porcupine grass, like that of 

 many other fine-leaved grasses, is cropped with relish by cattle and 

 horses. Sheep take a fair proportion of the herbage after the plant 

 has reached maturity, but the writer has never observed this class of 

 stock to graze porcupine grass as closely as cattle and horses unless 

 forced to subsist upon it. 



The seed heads of porcupine grass, unlike those of the wheat 

 grasses and many other grass species, are not particularly sought for 

 by stock, especially when the plant is approaching maturity or after 

 the seeds have ripened. In the first place, the seeds are rather small 

 and do not attract stock. In the second place, the basal portion of 

 the seed is sharp-pointed while the apex elongates into a rather 



