The distinct rhizomorphic mats formed by Piloderma fungi are significant features of the organic soil horizons of coniferous forests throughout the Pacific Northwest. These ectomycorrhizal (EcM) fungal mats have been found to cover over 40% of the forest floor in some Douglas-fir stands and are associated with a variety of physical and biochemical properties that distinguish them from the surrounding non-mat soils. As part of an NSF-funded Microbial Observatory at the H.J. Andrews Experimental Forest in western Oregon, we are examining the fungal and bacterial community dynamics of the EcM mats. Data from two studies will be presented: one focused on seasonal changes, and one focused on changes associated with the birth (or formation) and death (or decomposition) of mats. In each study, non-mat soils served as controls. As expected, microbial communities differed between mat and non-mat soils. Although QPCR revealed seasonal shifts in the population sizes, neither the bacterial or fungal community showed significant seasonal variation. In the two years following the establishment of the birth and death treatments obvious shifts in both the fungal and bacterial communities occurred. Although both treatments diverged from the mat and non-mat controls, the rate of the response varied. These results demonstrate that EcM Piloderma mats harbor unique and dynamic microbial communities.