Attached dead and partly living ash branches of (Fraxinus excelsior) were cut from mature trees and the three-dimensional structure of their decay communities analyzed. The communities were characterized by three Ascomycotina, seven Basidiomycotina and two Deuteromycotina, which varied in their ecological roles. The Ascomycotina Daldinia concentrica (Bolt: Fr.) Ces. & DeNot. and Hypoxylon rubiginosum Pers.: Fr. were pioneers growing in partly living or recently dead wood but causing only slow decay. D. concentrica is very combative and was apparently often able to persist until the wood was well decayed. Peniophora limitata (Fr.) Cooke was also probably a pioneer but tended to be found mainly in middle or terminal regions, as did Peniophora quercina (Fr.) Cooke on the few occasions that the latter was found. Both P. limitata and P. quercina caused extensive white rot. Exidia thuretiana was found fruiting on the bark but was not isolated from wood and appeared to cause cambial death. An unidentified ascomycete was also found in small superficial regions associated with bark death or wounds. Peniophora lycii (Pers.) Höhn & Litsch and Peniophora violaceolivida were secondary invaders usually found in distal regions which were subject to desiccation. Radulomyces confluens (Fr.) M. P. Christ was found in two branches in similar positions to P. limitata and P. quercina; its role was not completely clear but it was probably acting as a secondary colonizer. Mycoacia uda (Fr.) Donk was isolated once from terminal regions where it was replacing other species. In addition two Deuteromycotina, Phomopsis platanoidis Died, and a sterile unidentified sp., were isolated on a number of occasions, the former apparently resulted in little decay, although the latter was often found in decayed wood.