ACCRETION OR INCREMENT. 
35 
more saw timber than in the young grove above considered. 
For this reason, a good thicket of pine 60 years old may not cut 
much more than 6 M. feet per acre, since much timber is under 
sized, but the same stand at 120 years old would easily cut 15- 
20 M. in spite of the fact that over half the trees that were 
found in the 60 year grove have died before this age is reached. 
From this it would appear that 100 feet B. M. per acre and year 
on sapling timber is probably a safe estimate for the growth 
in this region. About the same conclusion will be reached if 
a grove of old hardwoods is considered. Such a grove, which 
may cut say 6 M. feet per acre,: will be found to consist largely 
of young trees, and among these 20-30 good sized older trees. 
If examined, it will be found that the age of the oldest is not 
over 150 years, so that here about one-third or less of all the 
trees standing on the acre have produced in 150 years the 6 M. 
feet B. M., which we are taking for lumber. The whole acre, 
therefore, may well be assumed to be able to produce this quan¬ 
tity in one-third this time, or in other words the same acre might 
be logged over for 6 M. feet about every 50 years. Such an 
assumption is fully supported also by comparing the cross-sec¬ 
tions of the pine and hardwood. These show that, though the 
rate of growth of hardwoods in Wisconsin is rather slow, yet 
the growth of oaks, basswood, etc., equals and excels that of pine. 
If, then, 100 feet B. M. per acre and year, be assumed as an 
average estimate of growth for this region, the total annual 
growth over the whole may be set at about 900 million feet B. 
M. and is distributed among the different kinds according to 
their ascertained acreage as follows: 
Million feet. 
White and red (Norway) pine.. 250 
Jack pine. 30 
Hemlock. 75 
Tamarack. 30 
Million feet. 
Cedar. 20 
Spruce and balsam. 10 
Hardwoods. 500 
915 
Of this growth the greater part is balanced by decay or nat¬ 
ural waste, which in all wild woods necessarily equals growth 
when large areas and long periods are considered. For white 
