PLATE 27 



A. Ceanothus oonsooies surrounded by Pinus ponderosa climax, which replaces it as a 

 result of competition for light, Spearfish Canon, Black Hills, South Dakota. 





B. Juniperus and Qitercus-Cercocarpus scrub colonizing a wind-swept Umestone ridge 

 without an intervening grass stage, Colorado City, Colorado. 



