HABIT. 



13 



irregular grain. The rate of growth often quickens as the tree pushes 

 up toward the light, and the grain becomes coarser and the wood 

 lighter. Red Fir, on the other hand, or Hemlock which has enjoyed 

 light in youth, shows a rapid growth near the heart and a slow growth 

 near the bark, when age has diminished the rate. 



A peculiar silvicultural problem is presented by the constantly 

 diminishing density of the Red Fir overwood. Nearl} T all Red Fir 

 forests start on burns or open land and are very dense for the first fifty 

 or one hundred years. The young Hemlock which starts beneath the 

 Fir during this period gets little light and grows slowly. Later, as 



20 40 60 80 100 120 140 160 160 200 220 240 260 280 300 



AGE- YEARS 



Fig. 2. — Diagram showing diameter growth of mature Red Fir and of Heniloek. calculated on a basis 



of age. 



the Firs begin to crowd each other out. more light is admitted and the 

 lower stoiy of Hemlock glows more rapidly. Hence, the older the 

 overwood the faster grow the Hemlock seedlings which come in beneath 

 it. The culmination of height growth as the Hemlock approaches 

 maturity therefore differs greatly from that under the usual forest 

 conditions where the supply of light remains constant. Instead of 

 falling off normally, as the trees approach maturity the growth of 

 the Hemlock forming the lower story is constantly stimulated by the 

 diminishing density of the upper story of Red Fir. (Figs. 1. 2.) 



