SILVICAL SYSTEMS IN NEW IIAMPSIIIRE 905 



raspberry and other brush is often very dense, and the hght is perhaps 

 not so good as in a high forest, yet the heat intensity is greater, for 

 the sun's rays strike the brush a foot or two above the young seedUng, 

 while in the high forest the heat is mainly absorbed by the mature trees 

 many feet above the little seedlings. 



"Trees with a strongly developed superficial root system naturally desiccate 

 the upper layers of the soil much more than trees with a compact, deep root 

 system." 



It naturally follows that if both softwoods and hardwoods arc removed 

 the young seedlings have only the brush to compete with for the mois- 

 ture. To quote further : 



. . . "the so-called 'light increment,' or increase of growth after logging or 

 thinning, is not due alone to the great access of light to the remaining trees. By 

 thinning a stand not only are the light conditions changed, but the competition 

 of the roots is diminished, which leads to an increase of moisture in the soil. 

 The leaf litter is also more rapidly decomposed, and the soil in this way becomes 

 enriched with nutritive substances, all of which results, of course, in an accelera- 

 tion of growth after thinning." 



In the foregoing discussion very little has been said alxiut incrcasetl 

 growth of the trees left through following a diameter limit when 

 logging. The theory of the diameter limit is that one aims to select 

 trees for cutting on a basis of age ; in actual practice in this locality the 

 cutting was based on size. 



DEFECTS OF A RIGID DI.VMETER LIMIT 



A rigid diameter limit presupposes a normal selection forest. As a 

 matter of fact, there is often a deficiency of thrifty trees just below 

 the diameter limit capable of growth, and not uncommonly a large 

 number of these are cut for skids, bridges, and other purposes in logging 

 the mature timber. The idea of the diameter limit is that the medium- 

 sized trees will take on growth, but elsewhere in this discussion it has 

 been shown that the growth did not increase as it was supposed to. 

 Moreover, no provision is made for the care of the reproduction. The 

 loggers often injure a large amount of it through carelessness. In 

 many instances in hardwood stands the removal of spruce leaves the 

 reproduction and the small-sized spruce still shaded. 



Formerly, when only large trees were merchantable, there was little 

 temptation to cut small timber, but under present conditions, with pulp- 

 wood at a ])remiinn, a 12-inch diameter limit on the stump means a 

 lO-inch limit under the old n'gimc of ax-cut trees and high sttnups. 



