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 su pported dense forest, have remained deforested. Surrounding areas in s imilar geomorphologic settings have returned to forest. We investigate d whether soil B horizon properties have degraded in response to the r emoval of podzolization-promoting vegetation by studying pedons under forest and stump prairie. Active soil processes were examined by analy zing ions sorbed on cation exchange resins and chelating resins that h ad been buried in the pedons, at three depths, for approximately 1 yea r. In both vegetation types, patterns of sorbed Fe and Al indicate tha t podzolization is on-going, with active translocation of sesquioxides into the B horizon. Larger absolute amounts of sesquioxides were sorb ed on resins in forested pedons compared with stump prairie pedons, ho wever, suggesting that podzolization processes are more active in fore sted than in stump prairie environments. The chemical and morphologica l properties of forested and stump prairie pedons were examined by ana lyzing the organic C and extractable Fe and Al content of horizon-base d samples. Strength of podzol development was greater, in general, for forested than for stump prairie soils. The primary chemical differenc e between the two types was found in organic C content and in properti es associated with organic C, including pyrophosphate-extractable Fe a nd Al. Differences between forested and stump prairie soils were much smaller for inorganic constituents. Depodzolization (the degradation o f existing podzol features) in stump prairie B horizons is most eviden t in morphological properties associated with organic C, which are dep endent on continued input of organometallic complexes. Depodzolization has occurred in the stump prairie soils because the balance between p rogressive development (podzolization) and regressive development (dep odzolization) has been altered under stump prairie vegetation.