Longevity of treethrow microtopography: Implications for mass wasting

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. Microtopography 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 geochronometric 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 (l) 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.