Longevity of
Treethrow Microtopography:
Implications
for Mass Wasting
Randall J. Schaetzl and Leon R. Follmer
This study examines and compares
methods of dating pit/mound microtopography formed by tree uprooting, and
provides 14C evidence for the longevity of these landforms. Microtopo-
graphy
can often by dated by reference to known meteorological phenomena, or within
certain age constraints, by dendrochronologic means. We used 14C analysis of buried wood and charcoal in
treethrow mounds in Michigan and Wisconsin, U.S.A. to arrive at estimates of
the geochrono-
metric ages of treethrow mounds. Results indicate that mounds in these areas often persist for more than 1000 years, which are two to five times longer than published estimates by less reliable methods. The longevity of treethrow mounds in these regions is ascribed to (1) sandy, porous soils which minimize runoff, (2) a continuous mat of forest litter and vegetation cover, (3) surface concentrations of gravel which may act as an armor, (4) large initial size of the features, and (5) soil freezing. Implications are that rates of mass movement due to uprooting may be substantially less than studies from other regions suggest.