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 (Pseudocymopterus-Mentzelia-chal- 
icium), stage III of the talus succession. 
308. Succession 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 
