Successional communities dominated by bracken fern (Pteridium aquilinum) establish on Andisols (Andosols) after removal of forest canopy in northern Idaho, USA. Many of these communities, known as bracken glades, have been created as a result of clear cutting over the past 50 yrs; others, based on radiocarbon dates, have apparently existed for millennia. We sampled Andisols supporting bracken glades ranging in age from 10 yrs to 7,700 yrs BP. Chemical and mineralogical characteristics of these soils were measured and compared to those of adjacent grand fir forest communities. Data show changes in several soil properties following establishment of bracken glades. Quantity and quality of belowground C increase as a result of bracken fern inputs in the form of rhizomes and fine roots (Fig. 1a). As much as 4.9 kg m^-2 of belowground biomass was measured in a 40-yr-old bracken glade, more than twice the amount in the adjacent forest. In addition, pH decreases and active forms of Al³⁺ increase (Fig. 1b). These changes are consistent with a conversion from allophanic to non-allophanic mineralogy. More surprisingly, our data indicate that this conversion is initially very rapid, occurring on a decadal scale. Properties observed within several decades of bracken fern establishment are similar to those of Andisols that have supported bracken glades for millennia.