to each other. It is a matter of common 

 observation that trees usually grow in 

 communities or societies, rather than as 

 solitary individuals. Sometimes there is 

 an extensive pure growth of a single tree 

 species, as in the case of some species of 

 pines, or tamaracks. Much more com- 

 monly one encounters mixed forests, 

 where two> or more species are growing 

 in the same society. . This condition is 

 admirably seen along river bottoms, 

 where ten or more species of trees are 

 commonly to be found together. It must 

 not be supposed that the "association of 

 trees in a society necessarily implies any 

 mutual relation between the various spe- 

 cies. A red oak may grow with a white 

 oak or a hickory, merely because each of 

 these three species delights in the same 

 kind of soil. It may be, and probably is, 

 a matter of utter indifference to any one 

 of these three kinds of trees whether the 

 others are present or not. But this 

 absence of a mutual relation is not found 

 in all cases. It is a matter for wonder to 

 many woodmen that when a forest of a 

 certain kind is cut down, it is succeeded 

 by a totally different type of forest. For 

 example, it is a matter of frequent expe- 

 rience in our northern woods that where 

 a forest of pines is cut away, a growth of 

 birch and poplar springs up in its place. 

 A hardwood forest is sometimes suc- 

 ceeded in a similar manner by pines. The 

 explanation of these phenomena is not 

 especially difficult." Birches and poplars, 

 as a rule, require a great amount of light 

 for their development ; the removal of 

 the pines gives such trees the very oppor- 

 tunity that they need, and they spring up 

 in profusion. Pines, on the other hand, 

 require, or at least can endure, a greater 

 amount of shade than birches or poplars, 

 but they do not thrive in dense shade as 

 do such hardwood trees as the sugar 

 maple and the beech. There would then 

 be a succession of trees in natural forests 

 about as follows : on a new area of land 

 one would find those trees which require 

 a maximum of light. These trees would 

 not be followed by their own kind, since 

 they cause a shade that is too great for 

 seedlings of their own species, though 

 well adapted for some other species that 

 requires a smaller degree of light. Again, 



this second species might not be suc- 

 ceeded by its own kind, but by a third 

 species which requires a still smaller 

 degree of light. At the end of the nat- 

 ural series would be those trees, which 

 can endure the greatest degree of shade. 

 The tendency thus would be for forests 

 to become less open and more shady from 

 decade to decade, and from century to 

 century. As forests become more shady, 

 moisture and forest mold become more 

 and more conserved, so that the forest soil 

 becomes richer and richer. In summation 

 we find that most forest trees bring about 

 conditions that are unfavorable for their 

 own kind and favorable for others, that 

 the first forests of a region are composed 

 of relatively light-loving trees, which do 

 not require a soil that is especially rich. 

 The later forests are composed of trees 

 which can endure denser shade and which 

 require a richer soil. When a forest is 

 destroyed, the density of the shade is 

 decreased, and the soil is exposed to sun 

 and wind, and consequently becomes less 

 rich. The result of course can be noth- 

 ing else than a backward step. An excel- 

 lent but saddening illustration of this 

 principle is to be seen in northern Mich- 

 igan, where the valuable pine forests, 

 which the lumbermen have destroyed, 

 have been succeeded by other trees of 

 but little value. 



In this contribution, only two or three 

 of the many tree problems have been 

 dwelt upon, but perhaps enough has been 

 said to illustrate the chief contention that 

 has been made, viz. : that the life prob- 

 lems of trees are as complex and mani- 

 fold and as real as the problems which 

 confront the lower animals and even man 

 himself. There is no field of study that 

 is more enticing, or more certain to yield 

 valuable results than the study of tree 

 problems. Nor is there any field where 

 there is more that is unknown, but yet 

 knowable, than here. The science of for- 

 estry, which is just now assuming a place 

 of great importance in this country, de- 

 pends for its ultimate success upon the 

 understanding of the tree, and apart 

 from any economic consideration, the 

 study of trees and their problems is one 

 that is certain to bring to its devotees 

 culture, health, and happiness. 



Henry Chandler Cowles. 



