22 



COMPOSITE TYPE ON THE APACHE XATIOXAL FOREST. 



Table 9. — Age, clear length, and total height in relation to diameter of western yellow 



pine in two forest types. 



Diam- 



Age. 



Clear length. > 



Total height. 



eter 



breast- 

























1 



high, 



Com- 



Yellow - 



Com- 



Yellow - 



Com- 



Yellow- 



outside 



posite 



pine 



posite 



pine 



posite 



pine 



bark. 



type. 



type.2 



type. 



type. 



type. 



type. 



Inches. 



Years. 



Years. 



Feet. 



Feet. 



Feet. 



Feet. 



12 



100 



98 



23 



7 



05 



49 



13 



107 



107 



25 



9 



69 



53 



14 



114 



116 



27 



10 



72 



57 



15 



122 



126 



29 



12 



76 



60 



16 



129 



136 



31 



13 



79 



63 



17 



136 



147 



33 



14 



83 



66 



18 



142 



159 



34 



16 



86 



69 



19 



152 



172 



36 



17 



88 



71 



20 



160 



184 



37 



18 



91 



74 



21 



168 



199 



38 



18 



93 



76 



22 



176 



214 



40 



19 



96 



78 



23 



184 



230 



40 



20 



98 



80 



24 



193 



247 



42 



20 



100 



82 



25 



202 



266 



43 



21 



102 



84 



26 



211 



286 



43 



21 



103 



85 



27 



220 



310 



44 



22 



105 



86 



28 



230 



339 



45 



22 



106 



88 



29 



241 





45 



22 



107 



89 



30 



252 





46 



22 



108 



90 



31 



264 





46 



23 



109 



90 



32 



277 





47 



23 



110 



91 



33 



292 





47 



23 



111 



92 



34 



307 





47 



23 



112 



92 



35 



325 





48 



23 



112 



93 



36 



344 





48 



23 



112 



93 



1 Distance from ground to first green limb. 



2 Stem analyses lor trees above 28 inches in the yellow-pine type are not at hand. 



The faster growth in the composite type is due to more favorable 

 site and climatic conditions. Since this type is found usually on 

 level areas, very little of it is subject to extreme exposure. In addi- 

 tion, the dense forest cover protects the soil and checks evaporation. 

 The precipitation, especially snowfall, because of the higher elevation, 

 is greater in the composite type than in the pure yellow-pine type. 



The difference in height growth in the two types is especially 

 striking. It is due in part to the superior site quality of the com- 

 posite type; but the greater density of stand is probably of the most 

 importance. Since only a small amount of light is received from the 

 sides, the trees respond to the stimulus of overhead light with a rapid 

 height growth. The difference in clear length is due entirely to the 

 greater amount of side shade in the composite type. 



Table 10, which is made from curves constructed upon the basis of 

 age, shows to better advantage the differences in diameter growth of 

 western yellow pine within the two types. It may be seen that up 

 to the age of 110 years the diameter growth in the western yellow- 

 pine type is greatest. But this is to be expected, since light conditions 

 in the openings which characterize this latter type are more favorable 

 than in the composite type, where there is a large amount of shade. 

 At the age of 110 } r ears the diameters are the same, but from this 

 point on the growth in the composite type increases until at the age 

 of 360 years there is a difference in diameter of 7.9 inches. 



