Crown Space of Western Yellow Pine. 333 



competition. In other words, the shutting off of part of the 

 sun's rays by the foliage of the big trees and the attendant de- 

 crease in evaporation from the soil more than offsets the moisture 

 absorbed by the large trees, and reproduction is consequently here 

 able to get a start, which would not have been possible for it in 

 the open. 



It has been frequently noticed in dense thickets of Lodgepole 

 pine where a few very large old larch were still left standing, 

 that the Lodgepole reproduction was very much thinner, or entirely 

 absent within 15 or 20 feet of the trunk of the larch. This cir- 

 cumstance was undoubtedly due to the fact that the large trees 

 absorbed so much of the moisture that none or little was left 

 for reproduction. Light did not enter into the matter to a 

 sufficient degree to account for the phenomenon, as very little 

 shade is cast by such trees. It must have been root competition. 

 However, as it would be impossible to grow Yellow pine of the 

 size of these larch within a distance of 40 or 50 feet of one an- 

 other because of the light requirements of the species, there is 

 no fear of root competition taking place to any serious extent. 



Were no other factor involved, it would be possible to judge 

 the correct spacing of Yellow pine according to the area oc- 

 cupied by the roots as judged by the crowns, and the approxi- 

 mate number of dominant trees that could stand on an acre 

 could be found by dividing the area of the crowns in square 

 feet into the area of an acre in square feet. But the light re- 

 quirements of the species compel a wider spacing of the trees 

 than is demanded for the development of the roots. 



(5) This extreme demand of Yellow pine for light, or intoler- 

 ance of shade, has played its part along with the other factors al- 

 ready mentioned, in keeping the forests composed of this species' 

 open. It will always necessitate that the trees be spaced well 

 apart. The crowns require light from the side as well as from 

 the top, in order that the tree may thrive and make good 

 growth. The large, irregular spaces primarily due to the rav- 

 ages of fire, insects, and wind are, however, entirely unneces- 

 sary and represent only so much waste ground from the stand- 

 point of timber production. Moisture, which might be available 

 for tree growth in these openings is now lost through evapora- 

 tion due to the unbroken rays of the sun and drying effects of 



