16 
With two exceptions, the figures are the actual averages 
obtained for each diameter class. This table shows that 
there is a much greater variation in the case of oak than is the 
case with ash. Yet both species occur together in the same 
stand. Oak demands space and struggles to obtain it. Its 
lower branches persist much longer than do those of ash, and 
this despite the fact that ash appears to be much more tol- 
erant of shade in the seedling stage. Oak will maintain a 
lower branch and thrust it out towards a source of light where 
ash would sacrifice the branch. 
Oak is similar to ash in that the height growth is not af- 
fected by the density of the stand. This is true, of course, 
only within certain limits; but so far as the tables given go 
those limits have not yet been reached. 
While total height is not affected by the degree of spacing, 
the length of clear bole is seriously decreased by the wider 
spacing. It will be seen that there is a gradual decrease in 
length of clear bole with increase of crown radius. When the 
crown canopy closes the lower branches are killed, and it 
comes about where the density was small in the early years 
that there is a big difference between length of clear bole and 
length to first living branch. In the larger diameter classes 
length of clear bole and length to first living branch usually 
coincide. This will be dealt with later when the trees will be 
grouped under bole classes of different lengths. 
In Table IX is given the yield per acre for an ideal stand of 
each diameter class given in the last table. The yields are 
taken from mill tally studies made on the Harvard Forest. 
The clear bole has been divided into the standard log lengths 
of the district eight, ten, and twelve feet and the board feet 
contents have been read from the log tables. 
