4. EQUILIBRIUM AT ARY POINT. 
Though the different tree species vary widely 
as to their relative production of seeds and seedlings, it 
seems certain that all are productive enough to be well 
within the limits required by nature. It has been pointed 
out by various observers that the "factor of safety” in 
seed and seedling production is very large and that there 
is an enormous wastage In all cases. While this larger seed 
production may be important on denuded areas, it seems clear 
that it has little to do with the relative number of in¬ 
dividuals of different species, where the dominant species 
are intensive, and where a balance has long been reached 
and maintained. This balance is changed little if any by 
excessive seed production of any species. It is conditioned 
by something more invariable than seed production. The true 
explanation seems to be the relative tolerance of the species 
for each other under the conditions imposed by the physical 
factors at that point. For example, the population of the 
yellow birch, which forms approximately 5^ of the total 
tree population half way up the north slope, is a measure 
of its relative response to the conditions imposed by 
the hemlock and maple. Since the equilibrium of the 
forest represents the result of the effective response of 
each species, the balance may be shown diagrammatically as 
