REPRODUCTION OF WESTERN YELLOW PIXE. 55 



accompanied by serious soil deterioration, excepting on steep slopes, 

 which occupy but a small portion of the total area. 12 Moreover, 

 western yellow pine does not require a fertile soil for reproduction, 

 provided the physical conditions are favorable. 



HERBACEOUS PLANTS As INDICATORS OF POSSIBILITIES FOR REPRODUCTION. 



The greater portions of the areas to be restocked with western 

 yellow pine are in the subclimax stage. This stage is represented in 

 various localities by various plant societies, depending upon the soil 

 and other factors. The key species in the most common subclimax 

 associations on the Colorado Plateau are Festuca arizonica. Muh- 

 lenhergia montana. Agropyron smithii, Sporobolus interruptus, 

 Bouteloua gracilis, and Andropogon scoparius. In the sample plots 

 3a and 3b, which are characteristic of the bunch-grass type of the 

 Coconino and Tusayan Forests, Festuca arizonica and Muhlenbergia 

 montana occur more or less in mixture, the former predominating on 

 the finer clay soils and the latter on the more stony or gravelly soils. 

 On the most prominent rock outcrops Andropogon scoparius is 

 usually present and often becomes dominant. 



The survey of sample plots 3a and 3b shows that yellow-pine re- 

 production is progressing better on the areas where Muhlenbergia 

 montana predominates than where Festuca arizonica predominates, 

 and that the very best reproduction occurs in the limited spots of 

 Andropogon scoparius. Although these differences are due primarily 

 to the influence of the soil rather than to direct effects of the grasses, 

 both factors appear to be important. Festuca arizordcfy for example, 

 thrives best in the finer clay soils in which yellow pine reproduces 

 with greatest difficulty : but the presence of this plant, which on such 

 sites becomes very tall and dense, creates still more adverse condi- 

 tions. Muhlenbergia montana predominates on the more stony or 

 gravelly soils, which in themselves are more favorable to pine re- 

 production, but on such sites the stand of grass is much lighter than 

 the Festuca arizonica stands. Thus we have the two favorable 

 factors, porous soil and light grass, associated on one side, and the 

 two unfavorable factors, heavy soil and tall dense grass, on the 

 other. Although the basic elements are not clearly differentiated, it 

 is believed that the relative dominance of three grasses mentioned 

 above may be employed as an index of possibilities for reproduction 

 of western yellow pine, the relative degree of favorableness being 

 in the order named. Until further studies are made, the applica- 

 tion of this relationship is restricted to soils of basaltic derivation 

 on the Coconino Tusayan National Forests. 



12 This apoliea to the Colorado Plateau. In certain other regions erosion is an im- 

 portant factor. 



