ROTATION AND DISTRIBUTION, 31 



the superior vigor of the hard-wood trees ; and they can 

 only maintain their supremacy on barren and sandy 

 levels, and the thin soils of mountain declivities, too 

 meagre to support the growth of timber of superior Icinds. 

 But a wood must stand a great many years, several cen- 

 turies perhaps, after its spontaneous restoration, before this 

 order of nature could be fully established. We must ob- 

 serve the spontaneous growth and distribution of herba- 

 ceous plants in different soils to ascertain these laws, 

 which are the same in a field as in a forest. 



When any growth of hard wood has been felled and 

 the whole removed from the ground, the soil, having been 

 exhausted of its potash, cannot support a new and vigor- 

 ous growth of the same kind of timber. TIae succession 

 win consist of a meagre growth of the same species from 

 seeds' already planted there ; but the white birch and 

 poplar, especially the large American aspen, usually pre- 

 dominate in clearings in this part of the country. When 

 a pine wood is felled, it is succeeded by an inferior growth 

 of conifers, and a species of dwarf or scrub oak. Seldom, 

 indeed, after any kind of wood has been cut down and car- 

 ried away from the spot, can the exhausted soil support 

 another that is not inferior in quality or species. Though 

 an oak wood may be succeeded by pines, a pine wood will 

 not be succeeded by oaks or any other hard timber, un- 

 less the trees were burned and their ashes restored to the 

 soil. Hence we may account for the fact that poplars, 

 white birches, and wild-cherry-trees, occupy a larger pro- 

 portion of the ground that is now covered with wood 

 than they did a century ago, in all parts of the country. 



I have already alluded to the well-known fact, that the 

 generic character of the timber, in the distribution of the 

 primitive forest, in any country, is determined in gi'eat 

 measure by the geological character of the soil. On 

 sandy plains in the primitive forest, the white birch, the 



