PURE AND COMPOSITE STANDS. 21 



A study of the columns headed " Periodic annual growth, per 

 cent," will give an idea of the amount of wood laid on in relation to 

 the size of the tree. It may be seen that this is at its maximum in 

 the early stages of development, and decreases steadily as the trees 

 grow older. The different species are alike in this respect. Since 

 the mean and periodic annual growth of western yellow pine and 

 Douglas fir correspond closely, there is but little difference in the 

 two species in respect to the annual growth per cent. Since both 

 the mean annual and periodic annual growth of spruce are greater 

 than those of either pine or fir, it would seem at first sight that the 

 periodic annual growth per cent would also be greater, though, in 

 fact, it is found to be much less. This is explained by the fact that 

 a greater growth is made early in life, and inasmuch as the principal 

 is larger the rate of growth in per cent is small, even though the 

 periodic annual growth or interest is large. 



COMPARATIVE GROWTH OF WESTERN YELLOW PINE IN PURE 

 AND IN COMPOSITE STANDS. 



Since there was an apparent difference between both the height 

 and clear length of western yellow pine in the composite type and in 

 the western yellow-pine type, measurements were taken on a total of 

 1,600 trees for comparison. The results are expressed in Table 9, 

 which gives the age, clear length, and total height in the two forest 

 types at each inch diameter class from 12 to 36. At a diameter of 

 12 inches the ages are practically the same; but from this point the 

 relative time required for trees in the yellow-pine type to grow one 

 inch in diameter increases, until at 28 inches it is almost three times 

 as great as for trees in the composite type. At this diameter there is 

 a difference of more than 100 years in the total age of trees in the 

 two types. 



The difference in clear length corresponds very closely to the dif- 

 ference in total height. At a breast-high diameter of 12 inches the 

 clear length of trees in the composite type is 23 feet, and in the 

 yellow-pine type but 7 feet. The difference steadily increases until 

 at 36 inches it is 25 feet in favor of the composite type. Trees in 

 the yellow-pine type are but 49 feet tall at a diameter of 12 inches; 

 at the same diameter and at approximately the same age, trees in 

 the composite type are 65 feet tall. The difference in height is 

 slightly greater at a diameter of 36 inches. 



