90 Alternations in Forest Growth. 



in height, and only two of these are conifers. By importation from 

 other countries, the number now under cultivation is largely in- 

 creased, and very many have been found entirely suited to the soil 

 and climate. Among these, the larch may be mentioned as the one 

 that has come into favor more than any other species, as a forest 

 tree, especially in Scotland. The conifers of our Pacific coast, and 

 especially the Douglas fir, appear in many cases to thrive well when 

 cultivated as timber trees. 



Alternations of Forest Growth. 



327. It has been often observed that when a forest has been de- 

 stroyed, and more especially if it has been killed off by fire, the 

 growth that succeeds, when left to itself, is very often of a different 

 kind. If the former growth was pine, the succeeding one may 

 be cherry or poplar, and in some regions oak. In the Southern 

 States, oak and hickory may be followed by pine. The white oak 

 cut off at Valley Forge by the American army in 1777-8 was fol- 

 lowed by black oak, hickory and chestnut. In Florida, the black- 

 jack (Querctis nigra) often follows the long-leaved pine (Pinus 

 australis). 



328. These facts have by some been regarded as favoring a theory 

 of rotation of crops in timber, by natural causes, as we practice 

 with advantage in agriculture ; but, according to the best received 

 opinions, this alternation is not a law of nature, but rather the re- 

 sult of external circumstances, which will generally be found suf- 

 ficient to account for all the facts we meet with. Either the decid- 

 uous or the resinous species can be introduced and maintained by 

 the aid of judicious cultivation, in places where the conditions for 

 their welfare exist in the soil or climate. 



329. But as different trees do not draw equally from the soil, we 

 should study the natural adaptation of the conditions of the local- 

 ity, and seek to accommodate the species to them, to the best ad- 

 vantage. In another part of this work, we notice some of the agen- 

 cies through which this natural seeding may occur. 1 



330. In seeking to continue the production of the same species 

 upon a soil where it has formerly prospered, we must never allow 

 the soil to become impoverished by the removal of the dead leaves 



1 See pages 30-33. 



