Complete Soil Profile Inversion by Tree Uprooting

 

Randall J. Schaetzl

 

            Treethrow pits and mounds in sandy Spodosols were examined to determine their internal soil horizonation.  Treethrow mounds were found to contain either (1) nearly intact, yet inverted soil profiles above otherwise undisturbed soil horizon sequences, or (2) more typical mixed and random horizonation.  Soil profile inversion, emphasized here for the first time, is initiated by treethrow on steep slopes which produces overhanging root plates.  Subsequent fire burns the trunk, eliminating all support and allowing the plate to overturn.  Charcoal within buried A horizons of mounds supports this hypothesis.  On gentle slopes, soil slumps off a more vertically-inclined root mass, resulting in a haphazard arrangement of horizons.  This arrangement occurs regardless of the presence of absence of fire, and results in the typical contorted horizonation often reported for treethrow mounds.