The Effects of Tree-Tip Microtopography on Soil Genesis, Northern Michigan
Schaetzl, Randall John
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https://hdl.handle.net/2142/70652
Description
Title
The Effects of Tree-Tip Microtopography on Soil Genesis, Northern Michigan
Author(s)
Schaetzl, Randall John
Issue Date
1987
Department of Study
Geography
Discipline
Geography
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physical Geography
Abstract
Seven sites in northern Michigan, each consisting of a treethrow pit/mound pair and an adjacent undisturbed site, were examined to determine: (1) the effects of uprooting on soil horizon disturbance; and (2) post-uprooting pathways of pedogenesis. On slopes of less than 25%, uprooting creates mixed horizonation within mounds. On steeper slopes a type of "inverted" soil profile is often observed in mounds, believed due to post-uprooting ground fire. Such fires consume the trunks and supporting roots of downed trees, allowing overhanging root plates and charred wood to settle onto the groundsurface in a relatively undisturbed, yet inverted, manner.
Buried wood and charcoal collected from within four mounds gave $\sp {\rm C}$ ages of 300-2010 years for uprooting events; 2-10 times greater than estimates for other areas. The longevity of the uprooting microtopography here is attributed to continuous litter and vegetation cover, extremely porous soils, relatively large initial mound sizes, and freezing of mound soils in winter.
In pits, soils (Spodosols) exhibit deep translocation of sesquioxides and organic carbon; mound soils are very weakly horizonated. Soil development indices show that pit pedons are equally, or more strongly developed than undisturbed sites, despite the much younger age of the former. Therefore, rates of pedogenesis in pits may be 5-10 times faster than on "normal" undisturbed sites. The rapid pedogenesis is partially attributed to greater leaching potentials caused by thick litter accumulations, which release larger amounts of organic acids than other sites, thereby accelerating development toward Spodosol morphology. Thin litter cover on mounds produces low amounts of organic acids. Leaching of organo-metallic complexes during the warm season is accomplished by a relatively few large, rain events, which effectively translocate more sesquioxides within pit soils than mound soils, due to more abundant organic acids and wetter initial soils.
During winter, mound soils often freeze because they are poorly insulated by litter and snow cover; pit soils usually remain unfrozen. Frozen mound soils are impermeable (concrete frost), whereas pit soils develop porous, granular frost. Whereas summer rains may leach all pedons to nearly comparable depths, snowmelt infiltration snowmelt is often blocked by frozen soil within mounds. Conversely, infiltration within pits and most undisturbed sites is unrestricted, resulting in maximal infiltration and leaching.
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