20 JOURNAL OF 1-ORF.STKV 



and red pine transplants three years old. A plot 52 by 52 feet was 

 laid out in this area in July last; the average crown density was 0.6 

 and the canopy extended to 22 feet above the ground. The overwood 

 was entirely gray, birch, which, when reduced to an acre basis, gave 

 1,232 stems per acre, of which number 338 were over three inches in 

 diameter, the larger being six inches one foot above the ground. The 

 average chemical light intensity under the canopy, based upon the 

 average of 20 exposures made by passing back and forth over the area 

 at six-foot intervals, was slightly more than 1/3 of full light. Height 

 growth measurements on the planted pine under the canopy were as 

 follows : 



Species Year Height growth in inches 



White pine 1917 3.3+ 



White pine 191S 5.4+ 



Red pine 1917 4-6+ 



Red pine 1918 4-5+ 



The height growth of both species averaged less ou those portio)is 

 of the measured area zchere they were exposed to full light for con- 

 siderable portions of the day. Under gray birch of the above density 

 there appeared as yet to be no apparent retarding of growth due to 

 shade. 



The following tentative conclusions have been drawn from this 

 study : 



(i) Pure stands of gray birch in southern New Hampshire are 

 never sufficiently dense to cause the death from shading of white pine 

 growing beneath. 



(2) Natural reproduction of white pine under gray birch is for the 

 most part of the same age as the birch. 



(3) The rapidity of height growth in white pine under gray birch is 

 dependent upon the density of the birch. 



(4) The falling off in height growth of white pine with increase in 

 the density of the gray birch overwood is chiefly due to competition 

 for soil moisture and nutrients and not to the density of the shade 

 cast by the birch canopy. 



(5) Pure stands of gray birch of all densities may be underplanted 

 with white pine and the birch removed when the slowing down of 

 growth in the pine or the economic utilization of the birch makes it 

 advisable. There is little danger that the shaded pine will be killed 

 by competition for light with the birch. 



(6) There appears to be a decided economic advantage in planting 

 white pine under gray birch over cutting the birch and planting later. 

 In the former case the need for cleanings to free the pine from sprouts 

 after the birch is cut is not so great. 



