HEIGHT GROWTH. 



33 



among the Hemlock, which stimulated the height growth of the piue during all its lifetime. The 

 White Pine on site Jc (Jefferson County, Pa.) was mixed with Hemlock of a small unmerchantable 

 size. The pine here had started simultaneously with the Hemlock, which stimulated the height 

 growth of the pine only for a certain period, after which the Hemlock, being overtopped by the 

 pine, was out of the struggle and left in the capacity of an underwood. The White Pine on site i, 

 which merged into site fc, was mixed with hardwoods, which stimulated the height growth of the 

 pine for the first sixty years, when the hardwoods reached their maximum height and then with- 

 drew from the competition, leaving the pine to increase the height on its own account. 



The influgnce of climate and soil on height growth will further appear from a study of the 

 tables in the Appendix. This influence on height growth is not very great, if we confine our 

 inquiry to regions of best development, the difference rarely exceeding from 5 to 10 per cent. 



20 40 60 80 100 120 /40 I BO 



AGE 



I'm. 3. Diagram showing height growth of White Pine in forest of varying composition in Pennsylvania: Site/, Clearfiehl C'onntyj sites 



k and i, Jefferson County. 



Effect of locality upon height groicth. 



Comparing the growth in different localities, it appears that the trees from Pennsylvania 

 started at a lower rate than those in all other localities, but after the twentieth to the twenty-fifth 

 year they surpass all others. If this can be accepted as correct, the deduction of the development 

 in early youth from old trees being subject to errors, it may be explained by the fact that these 

 trees grew in mixture with Hemlock and were kept back by the shade of their neighbors, but when 

 they had outgrown these they felt the stimulus exerted by them. 



The trees from Maine and Wisconsin, also starting more vigorously than those from Michigan, 

 decline and sink below the Michigan trees between the eightieth and ninetieth year, which may for 

 Wisconsin be possibly explained by the retarding influence of winds after the pines have out- 

 grown the hardwoods, while in Maine the poorer soil may account for it. Michigan, with its 

 tempered lake climate, presents a most regular and persistent height curve, coining nearest to the 

 average of all locations. 



In codominant and oppressed trees these differences do not come to an expression, but; since 

 the classification is somewhat doubtful and variations within wide ranges are possible, these data 

 are hardly to be used for comparison as to locality effects. 

 20233 No. 22 3 



