Regressive
Pedogenesis Following a Century of Deforestation:
Evidence for
Depodzolization
Linda R. Barrett and Randall J. Schaetzl
After the logging and fires of the
late nineteenth century, the upland stump prairies of Michigans 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 in 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. (Soil Science 1998; 163:482-497)