Recent research at the HJ Andrews Microbial Observatory showed that forest soil fungal communities responded in a dynamic fashion both to change in soil microclimate (forest vs. meadow incubation) and to the presence and absence of plant roots (open vs.closed soil cores). The current focus of our research at the HJ Andrews is to examine the composition and dynamics of microbial communities associated with specific ectomycorrhizal mat-forming fungal phylotypes. Our initial efforts showed that fungi from the genera Piloderma, Ramaria and Hysterangium were the major mat formers throughout the old growth coniferous forest at the HJ Andrews. PLFA analysis showed there were differences in the microbial communities associated with Ramaria mat versus non-mat soils, whereas differences were not apparent in the Piloderma mats using this method of analysis. Measurements of specific chemical and biological properties have shown some differences between mat and non mat soils. For example, concentrations of total oxalate were elevated in soils associated with EcM mats; this was most evident in mineral soils associated with Ramaria-type EcM mats. The potential for chitin degradation (N-acetylglucosaminidase activity) was higher in the organic horizon, and higher NAGase activity was associated with EcM mats. In the early summer of 2006, we established a reciprocal transfer experiment in which small soil cores were transferred from mats to non mat areas of the forest floor, and vice versa, in order to examine the dynamics of the biochemical and microbial community changes associated with birth and death of mats. Sufficient cores were established to enable sampling over a 3y period. The work presented in the poster will summarize our preliminary findings on this topic.