THE GEOGRAPHICAL DISTRIBUTION OF FORESTS 71 
globe communities of plants which can endure vary- 
ing degrees of cold, an excess or scarcity of moisture, 
or unfavorable soil conditions. The population of 
plants and animals is greatest in those regions where 
vegetation reaches its optimum, and decreases as one 
moves into regions where Nature’s ultimate resources 
become more and more meager or out of proportion. 
The simple fact, however, that a certain species 
may be found growing only in a very limited range 
is no reason for believing that it will not grow else- 
where. Many species which have been moved from 
their native place have met with new enemies and 
have perished; others, however, in being moved have 
escaped their foes, just as the American locust es- 
capes the borer in Europe. The forester is especially 
concerned with the possible range of all the species 
of important forest trees. The range of one species 
overlaps another depending upon its endurance or 
adaptability. In the zone in which the overlapping 
occurs, there is a change of neighborly relations of 
the species, and a varied rivalry in consequence. The 
red-cedar, for instance, beginning with Cuba and end- 
ing with Canada, passes through the natural ranges 
of many species. Because of its wonderful adapta- 
bility or versatility, it is a member of many com- 
munities. In the South it is a hydrophyte, or swamp- 
plant; in other places, it is a xerophyte, or drought- 
