INTERMEDIATE STAGES OF SUCCESSION 



215 



The fruticose lichens (Fig. 95) are upright forms and usually appear 

 later in the succession. On sand or clay-gravel the pioneer plants 

 are ordinarily annual xeric herbs. The pioneer plants of a hydrarch 

 succession are, of course, hydric, often floating or submerged, 

 plants, but even here the conditions are much more severe than in 

 later stages of the sere. 



Fig. 95.— a fruticose lichen. (Photograph by Bruce Fink.) 



132. Intermediate Stages of Succession.— The intermediate stages 

 include all of the stages between the pioneer community and the 

 climax. In the pioneer community there are relatively few species 

 and few individuals and the community is, therefore, more or less 

 open because the soil is not entirely occupied. The presence of the 

 pioneer plants, however, by checking the wdnd velocity, producing 

 shade, adding humus to the soil, etc., makes the habitat less extreme 

 and prepares it for the invasion of other species. The number of 

 individuals increases from the pioneer stage to the climax and the 



