22 FORESTRY BRANCH BULLETIN NO. 33 



brush is scattered too much to permit burning by any method other than burning 

 over the entire surface. However, a great deal of it is held off the ground so that 

 it becomes well dried, and, except where the site is very moist, the brush decays very 

 slowly and at a negligible rate. Even in contact with the ground, it rots slowly, and 

 the mere lopping of branches from the tops and scattering of brush so that it will 

 touch the ground does not recommend itself as likely to be attended with marked 

 benefits. Lumbered areas show slash lying after twenty years in a condition practi- 

 cally as dangerous as five years after logging. The effect of brush on reproduction 

 does not seem to be important. In general it retards it by increasing the thickness of 

 the litter and protecting and stimulating the growth of some forms of ground-cover. 



STIMULATED GROWTH. 



This phenomenon becomes important in the consideration of the direct benefit 

 to be derived from the growth of trees left for silvicultural reasons in stands being 

 logged. In many cases, the increase in volume during the period that the trees are 

 left yields a reasonable profit on the investment involved. This return is higher 

 than would be realized were the stand merely left standing without any cutting 

 having been done, because the admission of an increased amount of light increases the 

 rate of growth of the trees left. 



The different behaviour of various species under these conditions is very marked. 

 In general, the more tolerant the species, the better will it respond to increased light. 

 The branches of tolerant trees remain green well down the stem even in dense 

 stands, although they receive so little light that growth at the time is inhibited. On 

 the admission of more light by the opening up of the crown-cover, the dense deep 

 crown provides the machinery for increased volume production. Spruce, for these 

 reasons, will take advantage of any opportunities for increased growth offered to it. 

 Its habit of growing with a long cylindrical crown and drooping branches makes it 

 show greater and more immediate results from admission of increased amounts of 

 light than trees with wider, more spreading crowns. Fir is somewhat less tolerant 

 than spruce and has more horizontal branches and spreading crown; therefore, it 

 responds less to opportunities that may be offered to it for making more rapid growth. 

 Pine, being a very intolerant tree, loses its lower branches early and when grown in 

 dense stands has only a small crown at the top of the tree. If such trees are allowed 

 to receive increased light, they are unable to avail themselves of it until the crown 

 develops, which takes a long time. 



Stimulated growth is the result usually of the opening up of stands by either 

 fire or lumbering. Trees left after a fire are often very isolated and show extreme 

 increases in growth. Four firs left growing on an area fire-swept forty years ago, 

 averaged 0-23 inches diameter growth per decade before the fire and 0-54 inches per 

 decade after the fire more than double. After lumbering, the advantage to the 

 different trees of the stand is very variable. Some trees may be completely isolated 

 and show splendid increase, or the exposure may check their growth and injure the 

 crowns by sun-scald, &c. Clumps of small trees are often left intact and only a few 

 of them show any benefit from the opening of the stand. The necessity of studying 

 all the trees on specified areas, if an accurate idea is to be obtained of the actual 

 results, is evident. 



Three plots were taken in stands logged twenty years ago, leaving fifty to one 

 hundred trees, eight inches to twelve inches in diameter, per acre, and showed the 

 following per cent growth in cubic feet for the two decades both preceding and follow- 

 ing the logging: 



