Regressive pedogenesis following a century of deforestation: Evidence for depodzolization

After the logging and fires of the late nineteenth century, the upland stump prairies of Michigan's Upper Peninsula, which had previously supported dense forest, have remained deforested. Surrounding areas in similar geomorphologic settings have returned to forest. We investigated whether soil B horizon properties have degraded in response to the removal of podzolization-promoting vegetation by studying pedons under forest and stump prairie. Active soil processes were examined by analyzing ions sorbed on cation exchange resins and chelating resins that had been buried in the pedons, at three depths, for approximately 1 year. In both vegetation types, patterns of sorbed Fe and Al indicate that podzolization is on-going, with active translocation of sesquioxides into the B horizon. Larger absolute amounts of sesquioxides were sorbed on resins in forested pedons compared with stump prairie pedons, however, suggesting that podzolization processes are more active in forested than in stump prairie environments. The chemical and morphological properties of forested and stump prairie pedons were examined by analyzing the organic C and extractable Fe and Al content of horizon-based samples. Strength of podzol development was greater, in general, for forested than for stump prairie soils. The primary chemical difference between the two types was found in organic C content and in properties associated with organic C, including pyrophosphate-extractable Fe and Al. Differences between forested and stump prairie soils were much smaller for inorganic constituents. Depodzolization (the degradation of existing podzol features) in stump prairie B horizons is most evident in morphological properties associated with organic C, which are dependent on continued input of organometallic complexes. Depodzolization has occurred in the stump prairie soils because the balance between progressive development (podzolization) and regressive development (depodzolization) has been altered under stump prairie vegetation.