INVASION AND SUCCESSION 



281 



an immense number of successions, among which those of burned, 

 lumbered, or cultivated areas are far the most frequent. 



302. Succession in burned areas. From the nature of the 

 vegetation, fires are of little significance in open formations, such 

 as deserts, wastes, etc. In grassland the living parts are under- 

 ground at the time when fires ordinarily occur. In consequence 

 the annual burning of prairie or meadow disturbs the formation 

 very little, and no succession results. All formations composed 

 of woody plants, e.g., forests and thickets, are seriously injured 



Fig. 116. An aspen forest, the typical stage of the burn succession. 



by fire. A severe general fire destroys the vegetation completely. 

 A local fire destroys the growth in a restricted area, while a super- 

 ficial burn removes the undergrowth and hastens the disap]:)ear- 

 ance of the weaker trees. A local fire prepares the way for a 

 succession in which the invaders come largely from the original 

 formation, especially when this encloses the burned area more 

 or less completely. When a particular formation is destroyed 

 wholly or in large part, the first stages of the new vegetation are 

 formed by invaders from the adjacent formations. The sue- 



