crops by Studying the height and diameter and volume of growth 
ot the various size classes, together with the gradual diminution in 
numbers which takes place in a fully stocked crop. 
1 hese measurements show that the same acre always produces 
annually the same weight of dry wood, with practically whatever 
species it may be grown, namely, from 4,000 to 8,000 pounds per 
acre, according to the quality of the ground. The volume may 
vary according to the specific gravity of the wood of different 
species, and according to '.lie water contents. The annual pro- 
duction of available dry wood substance above ground varies, 
accoiding to the quality of the climate and soil from 3,500 pounds 
on good sites to 1,200 pounds on the poorest. The number of trees 
to the acre is ol no consequence, provided that a full crown cover 
is always kept. ” 
I have on previous occasions given expression to the fact that 
overcrowding should be avoided and most practical men are agreed 
on this point, but the question that arises is — what constitutes over- 
crowding? Let us take a hint from nature. 
Dr. Fernow tells us that in a pure forest of one species (and a 
rubber plantation may be regarded as such) the individual trees of 
different sizes develop side by side according to available light, 
each crowding the other, until the laggards are killed by the with- 
drawal of light. 
As an example of this he instances a stocked acre of American 
white pine, containing 50,000 or more seedlings in a dense thicket, 
excluding all light from the soil. “ After a few years the lower 
branches owing to the absence of light die and fall off— in the case 
ol tropical products where the rate of growth is much more rapid 
this would occur after a few months. At 30 years old the trees 
are slender poles of about 4 inches diameter and 20 to 25 feet in 
height ; but different degrees of vigour of development, according 
to individual constitution and accidental opportunity, can now be 
recognized, and three classes may be differentiated : the predom- 
inant, with their crowns 5 to 10 feet above the general level, which 
are the trees of the future; the sub-dominant, ready to occupy the 
air-space of any o! the superior class should accident remove any 
ot them ; and lastly, the suppressed ones, doomed to die. ” 
Out of the tens of thousands which started, only 2,000 or 3,000 
survive, and as each tree is striving with its neighbours for as much 
air-space and root-space as possible, the result is a continued di- 
minution of the number of trees occupying the acre.” 
1 his decimation is in exact mathematical relation, barring ac- 
cidents, with the development of the dominant class in height- 
growth. ” 
‘At the age of 80, not more than 400 to 500 trees are left. 
After this age the diminution proceeds more slowly until at last 
only 200 or 300 stems occupy the ground, the number varying with 
species, soil and climate. ” 
We see then that out of 50,00 s seedlings no less than 49,800 
