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.