Timber Growth and Drain 
SS 
Current Growth 
in the Upper Peninsula, the cut-over and burned- 
over lands are slowly restoring themselves to a 
productive condition. On the 4 million acres of 
restocking land, the annual rate of growth, com- 
puted for the next 10 years, averages 19 cubic feet, 
or about one-fourth cord per acre. A little more 
than half of this growth consists of pines, spruces, 
sugar maple, and other valuable species. The 
other half is aspen, paper birch, scrub oak, red 
and silver maples, and miscellaneous inferior 
hardwoods. If this rate of growth is maintained 
most of these restocking areas will become cord- 
wood forests within 20 years, but spruce and tama- 
rack swamps will require at least another 40 years 
to reach cordwood size. (See table 23, Appen- 
Cordwood stands, which cover nearly 1% million 
acres, are growing at the rate of 29 cubic feet per 
acre per year, about two-fifths of a cord. Two- 
thirds of this new volume is aspen, paper birch, and 
other inferior hardwoods. Second-growth saw- 
timber stands, covering three-quarters of a million 
acres and containing nearly 3 billion board feet, 
are growing at the rate of 91 board feet per acre. 
Only one-third of this is of inferior species. 
The 1.7 million acres of old-growth saw timber, 
which contains most of the merchantable timber 
in the Upper Peninsula, has an average net annual 
increment of 72 board feet per acre. This rela- 
tively low rate, less than 1 percent of the base 
volume, is to be expected in mature and overma- 
ture stands where most of the growth is offset by 
death and decay. Undisturbed overmature tim- 
ber does, of course, eventually reach a static con- 
dition with growth being entirely offset by death 
and decay. In the Upper Peninsula, however, 
many of the mature hardwood stands have been 
disturbed by the cutting of white pine and a few 
hardwoods in earlier years and the gaps caused by 
this cutting are still being filled. 
I: SPITE of the clear-cutting practices and fires 
st) 
The total current annual increment in the Upper 
Peninsula is 343.5 million board feet. Of this 
total, 189 million board feet is in saw-timber 
stands, while the remainder is largely in scattered 
saw-timber trees in stands which are still unmer- 
chantable except for cordwood products (table 
10). 
Tasie 10.—Current annual increment in each size class of stand} 
Sawlog volume Total volume 
Size class 
Per acre Total Per acre Total 
Board M board Cubic M cubic 
Jeet feet feet feet 
Old-growth stands_-_-_-_-_---- 72 120, 300 13 21, 900 
Second-growth stands_____-_- 91 68, 800 15 11, 000 
Cord:wood'stands__--------=- 58 | 100, 300 29 51, 600 
Restocking areas_____-_---_-- 12 49, 600 19 74, 200 
Deforested areas_____________ 4 4, 500 2 2, 200 
Average and total______ 37 | 343, 500 18 160, 900 
1 Estimated for decade 1940-49. 
Allowable Annual Drain 
Current increment is only one of the factors 
determining how much timber should be removed 
from the forest each year. Another consideration 
is the condition of the growing stock. If the forest 
is overmature and overstocked, more volume can 
be removed than is replaced by growth until the 
forest is brought to a thrifty growing condition. If 
the stands are young and understocked, the annual 
removal should be less than current growth until an 
adequate growing stock has accumulated. Re- 
moving the entire current increment would serve 
to keep the forest permanently in an understocked 
condition. 
Another factor is the method of cutting. Other 
things being equal, more timber can be cut 
annually if the method of cutting is such as to 
stimulate growth on the remaining stand and if all 
trees are cut at the right stage of development. 
Destructive logging and removal of immature 
