RELATION OF GRAY BIRCH TO WHITE PINE 17 



density of 2,198 hardzvood stems per acre, chiefly gray birch, zuith the 

 trees 24 years old, from one to six inches in diameter and averaging 28 

 feet tall, there appeared to be no loss of zvhitc pine due to overshading. 

 There had, however, been a remarkable reduction in growth as com- 

 pared with Plot I. On Plot I but 22 pines per acre were below two 

 feet. in height, while on Plot II over 800 per acre were below. More- 

 over, the smaller pines were of the same age as the larger ones, being 

 held back, due to the keener competition with the hardwoods. On 

 Plot II, however, with 2,198 hardwood stems per acre, from one to six 

 inches in diameter and 28 feet in average height, no pines had been 

 killed through competition with the overwood, although they had been 

 greatly checked in growth as compared with Plot I. 



The annual height growth of the pines on Plot II during the past 

 four years showed the average annual growth to be as follows : 



Vear Height growth in inches 



1915 54+ 



1916 5.8+ 



1917 5.1+ 



1918 34+ 



The growing season following the uncovering of the pine height 

 growth was greatly reduced, although the trees appeared more vigorous 

 and the needles were larger and more numerous. Not only in this 

 instance, but in five other cases where measurements were taken on 

 pines uncovered during other years, height growth the season follow- 

 ing the removal of the overwood was reduced from 30 to 60 per cent 

 from the average of the three years preceding its removal. 



Plot III, with a very dense overwood of hardwoods, chiefly gray 

 birch, when reduced to an acre basis, had 2,374 hardwood stumps per 

 acre, with gray birch forming nearly all of the larger sizes and aver- 

 aging considerably larger than on the two previously described plots, 

 approximately 75 per cent being above three inches in diameter, while 

 on Plot II less than 50 per cent were above three inches in diameter. 

 It was clearly evident from the size and number of the hardwood 

 stumps that Plot III had a much denser hardwood canopy before its 

 removal in the winter of 1917-18 than either of the other two plots; 

 moreover, the ground was lower and the soil moister. Not only were 

 the gray birch stems larger and more numerous, but red maple, to 

 considerable extent, replaced aspen in mixture with the birch. Plot 

 III, with its great density of 24-year-old hardwoods, had in its under- 

 story 860 white pine trees per acre. They were, as in the other two 

 cases, of the same age as the hardwoods. Over 70 per cent were less 

 than two feet in height, about 10 per cent were over four feet tall. 



