42 THE BOOK OF FORESTRY 
climates and the age must be guessed at according to 
the size of the tree. 
During the early life of a tree height growth is quite 
rapid, the reason being that unless it is shade-enduring 
it must outgrow its competitors to obtain sufficient sun- 
light. During this period the struggle for existence is 
very keen in the young forest and many little trees 
are crowded out and die. After the period of rapid 
height growth has passed a tree begins to take on flesh— 
to increase in diameter and volume. In this respect 
trees are like some fast-growing boys, quite weedy and 
slim for a few years and then gradually becoming stout 
and strong. . 
How Trees Reproduce Themselves.—About the time 
the diameter growth is beginning to increase and a 
surplus of starch has been stored in the roots, etce., 
the tree is ready to produce seed, for seed produc- 
tion is largely a matter of sufficient food. When 
there has been a series of favorable years with 
plenty of rain and yet sufficient warmth and sun- 
light trees will produce large quantities of seed. These 
seasons of bountiful seed production are known as 
‘“seed years,’’ although a little seed is produced nearly 
every year. These seed years come at unequal in- 
tervals depending upon the fortune of the tree three to 
five years previous. Seed years are not uniform within 
the species all over its range, as the white pine of the 
Lake States may bear a heavy crop of cones while the 
white pines of Maine will be absolutely barren. Trees 
growing in the open produce seed in larger quantities 
and at an earlier age than trees in the dense forest. 
As a rule trees in the open will commence to bear 
fertile seed at twenty-five years while those in the 
forest are incapable of producing a crop of seed until 
