32 



THE WHITE PINE. 



to make as gx<l uu animal height growth as its more-favored neighbors, and can continue the 

 same to the second century. From the table of heights at various ages it is learned that the 

 success in the juvenile stages after all tells on the total height growth. 



T MU.K IV. Periodic height growth, by decades, of dominant, codoninant, and oppressed pint. 



Effect of composition of forest upon height growth. 



The height development of White Pine seems to progress more rapidly when it grows mixed 

 with other species. A striking instance showing how the height growth of White Pine is bene- 

 fited by the presence of other species is given in the diagram (fig. 2), which represents the height 

 growth of White Pine taken from two sites ( and 6) in Presque Isle County, Mich. The sites 



were about 5 or 6 miles distant from each other. 

 The soil and the moisture conditions on both 

 sites were apparently identical (fresh sand), as 

 were the total number of trees to the acre (the 

 sample area on site a contained 181 trees and 

 that on site & 189 trees) and the age of the trees 

 and their distribution over the ground (density 

 of crown cover). The only difference found be- 

 tween the sample areas staked off on both sites 

 was the composition of the forest. Site a con- 

 sisted of a mixed growth of Norway and White 

 Pine, while site b represented practically a pure 

 growth of White Pine save a few small Hemlock 

 and an occasional Norway Pine. The diagram 

 shows that the White Pine on site a was exceed- 

 ingly stimulated in its height growth by the 



40 60 

 RGE. 



presence of the Norway Pine. 



The associated species entering into the 

 struggle for light with the White Pine naturally 



affect the P^ 88 of the hei s bt e rowth of the 



pine. The effects of the associated species upon 

 the height growth of White Pine and the period of their influence depend npoii the capacity of 

 the associated species to grow in height as well as upon the time when the associated species are 

 either introduced among the pine or received it under their shelter. In case, for instance, hard- 

 woods accompany White Pine from the very start the influence of the hardwood upon the height 

 growth of the pine will last only for the first sixty or seventy years, that is, up to the age at which 

 most of the hardwoods practically reach their maximum height. In case the Norway Pine or the 

 Hemlock starts simultaneously with the White .Pine, the height growth of the White Pine will be 

 stimulated to a considerably later age, because the Hemlock or Norway Pine continues to grow in 

 height at a similar rate for a longer time. When the White Pine happens to start on ground 

 already covered with other species in such a manner as not to be interfered with in its growth the 

 associated species, if capable of growing in height to a later age, will stimulate the height growth 

 of the White Pine for a considerably longer period. All this is clearly demonstrated in the accom- 

 panying diagram (fig. 3), representing the height growth of White Pine taken from three sites 

 (/, fr, and t) of identically the same conditions except as to composition of the forest and the differ- 

 ence in the ages between the pine and associated species. All three sites had a well drained 

 clayey loam underlaid by a laminated shale of indefinite depth. The White Pine on site/ (Clear- 

 field County, Pa.) was mixed with Hemlock of a large size; the pine on this site had started 



