252 



THE FORMATION 



In the most perfect types of succession, this dissimilarity between the new 

 and the old vegetation continues to the last stage, in which the reappearance 

 of the facies precedes that of the subordinate layers. In many forest suc- 

 cessions, however, the general physical similarity of the ultimate stages per- 

 mits the early reappearance of the herbaceous and shrubby species, and the 

 final stages affect the facies alone. Successions in burned areas operate usu- 

 ally within the water-content groups. The reconstruction of a mesophytic 

 forest takes place by means of mesophytes ; of the rarer xerophytic and hy- 

 drophytic forests, through xerophytes and hydrophytes respectively. This 

 is due to the fact that the alteration of the soil is slight, except where the 

 burning of the vegetation permits the entrance of erosion, as on mountain 

 slopes. 



Fig. 64. Gravel slide formation (Pscudocymopterus-Mcntzclia-chal- 

 tcium), stage III oi the talus succession. 



308. Succe5sion in lumbered areas. Commercial lumbering, especially 

 where practiced for wood-pulp as well as for timber, results in complete or 

 nearly complete destruction of the vegetation by removal and the change 

 from diffuse light to sunlight, or by the action of erosion upon the exposed 

 surface. In the first place, short mesophytic successions will result; in the 

 second, the successions will be long and complex, passing through decreas- 

 ingly xerophytic conditions to a stable mesophytic forest. Where a forest 



