One frequently finds small patches of fir in which the number of trees on an acre was much higher than given in the table above. For example, four-year-old stands sometimes ran as high as 322,000 little trees upon an acre, and even in the 16- and 18-year-old stands the number per acre frequently reached 30,000. The figures in the table, however, give a good idea of the general condition of the reproduction, including the poor as well as the good.
The table above clearly shows the natural thinning-out that takes place as the trees increase in age and size. In the case of the 57,600, less than 10 years old on an average acre, each little tree occupies less than a square foot of soil. If all of these trees lived until they were a foot in diameter, the result would be a solid block of wood upon an acre. We know that trees do not grow that way. There is not room enough for them all, so the weak die and the strong survive. As shown by the table, in this case 91 per cent of the trees had died by the end of the nineteenth year, 97 per cent at the end of 29 years, and 98 per cent