REPRODUCTION OF WESTERN YELLOW PINE. 47 



clumps, in providing soil cover and organic matter to relieve the 

 clayey character of the soil (PI. VII, Fig. 2). Another important 

 factor, as will be shown later, is the protection which the unpalatable 

 weeds afford against damage by grazing. 



The above relation is not confined to the extremely heavy clay soils ; 

 it prevails generally on the volcanic soils throughout the yellow-pine 

 type. It was first observed in the cinder region east of Flagstaff 

 in 1908. Here the adverse conditions are not due to compactness of 

 the surface, but. on the contrary, to excessive looseness and coarse- 

 ness, and consequent inability to hold moisture. Where the cinders 

 are deep, seeds rarely germinate except in dense shade, in leaf litter, 

 or in bunches of grass or weeds. On such sites seedlings almost 

 invariably occur in tufts of grass. Plate VIII, Figure 1, shows a 

 seedling about 10 years old in a tuft of bluestem grass (Andropogon 

 scoparhis). The grass is dying out in the center of the tuft, and in 

 a few years will have disappeared. 



Plate VIII. Figure 2, shows a tuft of Festuca amzonica on a loamy 

 clay soil in the region west of Fort Valley. Xo less than 12 seedlings 

 of 1919 germination were counted in this tuft, most of them along 

 the northern periphery. As may be seen from the photograph, the 

 tuft is dying out in the middle. This is a common habit of the bunch 

 grasses in this section. In old tufts the hollow spaces in the middle 

 are from 4 to 6 inches in diameter, leaving only a fringe of live stems 

 in the periphery. The interior is a mass of dead stems and roots, 

 more or less decomposed and forming an excellent place for young 

 seedlings to establish themselves. It should be noted also that the 

 grass has been only partially grazed off. The remaining stems, 

 about 6 inches tall, are too coarse to be relished by stock, and there- 

 fore stand through the winter and furnish protection to the seedlings. 



LATER DEVELOPMENT RETARDED BY HERBACEOUS COVER. 



As previously intimated, the protection afforded by herbaceous 

 vegetation is not an unmixed blessing. After pine seedlings have 

 passed through the first winter they do not need this protection 

 (except against sheep grazing), but they do need the moisture and 

 sunlight which are preempted by the larger plants. Studies during 

 the summer and fall of 1920 demonstrated these relationships in a 

 striking manner. 



Stump patches. — When an area is logged there are left numerous 

 bare patches formerly occupied by groups of trees. For convenience 

 in reference these spots will be designated " stump patches," since 

 the stumps of the felled trees always occupy the central portion. 

 If the tree groups were large, the space underneath the crowns and 

 for a distance of about 30 feet to the north will be found to be 

 practically bare of grasses. If grazing animals are excluded, the 



