INTEODUCTION. 129 



In the growing of a group, plantation, or forest, 

 several important changes are gradually yet imper- 

 ceptibly taking place upon the trees both individually 

 and collectively, — upon the soil on which they grow, 

 upon the surrounding atmosphere and climate, and 

 consequently upon every subject in the whole neigh- 

 bourhood and district. 



What these changes are, how they are produced, 

 what takes place when the produciag causes or active 

 influences are removed, are considerations alike im- 

 portant and worthy of investigation. It is self-evi- 

 dent that as two or more trees approach each other 

 — which they do in a threefold way, namely, by the 

 points of the lateral branches elongating themselves 

 and annually extending their young shoots, by the roots 

 mixing, interlacing, and' sometimes even grafting each 

 other in their subterraneous ramifications, and in the 

 annual enlargement and increased diameter of their 

 stems or trunks^other and different changes are also 

 produced upon the soils in which the trees grow, and 

 different species of trees also produce different results. 



The changes produced upon the soil may -also be 

 regarded as of a twofold nature — namely, chemical 

 and mechanical. The chemical changes produced are 

 alike obscure, difficult to trace or comprehend ; nor 

 has science done much, if anything, to throw light 

 upon the dense darkness, or reveal what is unknown 

 or hidden. That the constituent parts of the soil are 

 not the same after having produced a crop of wood or 

 timber as they were before is certain, but whether the 

 change is produced by something being abstracted or 

 imparted, is, and may remain long, a mystery. The 

 mechanical changes produced, however, are most ob- 

 servable and obvious to the senses. The roots of the 



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