CLIMAX COMMUNITIES : SHIFTS WITH TIME 



311 



cept may be applied to individuals or a species, but is more often 

 used for communities. It may be used to describe delayed or lag- 

 ging stages of succession, but it has far greater usefulness in con- 

 nection with climax vegetation. 



The usefulness of relicts lies in their indicator value of past con- 

 ditions of habitat and vegetation as well as of the causes underly- 

 ing changes that have occurred elsewhere in the area. A relict 



! 



FlG. 167. Relict (postclimax) black spruce forest in a Minnesota bog.— 

 U. S. Forest Service. 



community having remained relatively unchanged because of pe- 

 culiar local conditions is an actual sample of, or shows strong 

 similarities to, previous vegetation. At the same time, the peculiari- 

 ties of the relict habitat are indicative of environmental conditions 

 previously characteristic of the area as a whole and may, therefore, 

 be suggestive of why vegetation changed generally there. 



Relict communities occur where local edaphic, topographic, or 

 biotic factors differ sufficiently to compensate for the effects of 

 environmental conditions obtaining generally. Thus altitude, ex- 

 posure, or soil may provide locally unusual moisture conditions. 

 Ridges, streams, and lakes may constitute barriers to fire. Peculi- 

 arities of drainage may result in swamps, bogs, and low flood 



