70 PRACTICAL FORESTRY 
become adapted to all sorts of conditions, the ideal 
condition in which most plants reach their optimum 
is in a climate in which there is never frost, in which 
there is always sufficient warmth and moisture, and 
in which the soil is of the proper quality both chem- 
ically and physically. In such an environment the 
struggle for existence is not against the parsimony 
of Nature, but between the individuals which con- 
stitute the community. 
Every clime is capable of supporting a certain 
number of living things in proportion to its natural 
resources. These ultimate resources are sunlight, 
warmth, moisture, and suitable soil. In the presence 
of the proper proportion of these conditions, vegeta- 
tion reaches its maximal growth. The vegetal, and: 
especially arboreal population of such a region is usu- 
ally extremely high, so high, in fact, that the struggle 
between the members of the community is most in- 
tense. Every individual must fight incessantly in 
order to hold sufficient space in which to grow. These 
ultimate resources do not exist throughout the whole 
world in the proper proportions. Whenever there 
is proportionately too little or too much of any one 
of these resources, then there begins a struggle with 
the environment, and only those species survive 
which are able to endure the abnormal condition. 
Therefore, we have, distributed over the face of the 
