﻿12 BULLETIN 13, U. S. DEPAETMENT OF AGEICULTUEE. 



ment. It succumbs to shade much more quickly than hemlock, 

 spruce, beech, or maple, but needs less light than red, pitch, or jack 

 pine, gray birch, or aspen. 



The less light a tree receives the slower will be its growth, and if 

 shaded beyond a certain point it will die, practically from starvation. 

 A suppressed tree to which light is admitted will respond in a greater 

 or less degree, according to the length of time it has been suppressed, 

 by putting forth new foliage and increasing its rate of growth. White 

 pine does not possess the power to recover from suppression to the 

 extent shown by hemlock, spruce, or fir, which will exist for years 

 under heavy shade, and then, with the admission of light, spring at 

 once into rapid, vigorous growth. If not too long suppressed, white 

 pine will usually recover to some extent when released, though its 

 subsequent growth is apt to be less thrifty than that of unsuppressed 

 trees. 



The trees more tolerant of shade naturally produce more foliage 

 and themselves cast more shade than those less tolerant^ and it is 

 for this reason that white pine seedlings under maple, beech, hem- 

 lock, or even heavy white pine crowns, can not grow. Under the 

 light shade of aspen, paper birch, or other intolerant trees young 

 white pine often receives just enough light to keep it alive and to 

 stimulate a rapid height growth, which results if the soil is good 

 enough, in its eventually overtopping and displacing the other 

 species. When mixed with heavy foliaged hardwoods or hemlock 

 white pine crowns almost always project above the general level of 

 the crown cover. In such stands the pine is able to reproduce itself 

 only when its seeds fall in chance openings large enough to admit 

 full light during the period necessary for the tops of the young trees 

 to reach the level of the crown cover. 



Since white pine is more tolerant of shade than is red pine it is 

 able to grow in much denser pure stands and hence will produce a 

 greater amount of wood per acre. 



Young white pines have a symmetrically conical form, due in large 

 part to the fact that the branches grow in whorls. A whorl of 

 branches marks each season's growth, so that two contiguous whorls 

 afford a means of determining the height growth for a given year, and 

 all the whorls together the approximate age of the tree. Each suc- 

 cessive whorl shuts off light from the ones beneath, and these must 

 increase in length if they are to continue to function. In the stand 

 tliis increase is checked by the branches of adjacent trees, while in 

 the open it is limited only by natural forces, chiefly gravity. In 

 consequence, the crowns of open-grown trees are often broad pyra- 

 mids reaching close to the ground. 



