Effects of Treethrow Microtopography on the Characteristics

and Genesis of Spodosols, Michigan, USA

R. J. Schaetzl

This study examined the pedogenic effects of pit and mound microtopography, formed by tree uprooting, in a Spodosol (Haplorthods) landscape. Most soils in treethrow pits were Entic Haplorthods or Spodic Upidsamments whereas mound soils usually classified as Typic Udipsamments, suggesting that degree of profile development is: Undisturbed Pit > Mounds. Given that pit and mound soils are substantially younger than pedons on undisturbed sites, rates of pedogenesis are thought to be: Pit > Undisturbed > Mound. Strong pedogenesis in pits was explained by :

1. greater water contents in the upper sola, which may facilitate weathering processes,

2. thicker O horizons, which may lead to increased production of organic acids, and

3. greater insulation by thick litter and snow cover, which reduces the incidence of soil

freezing.

In winter, mound soils may develop impermeable layers of concrete soil frost that impede infiltration of snowmelt waters, whereas pit soils remain unfrozen or acquire only a porous, granular frost layer. Thus, saturated flow of snowmelt within pits is relatively unrestricted, resulting in maximal leaching and profile differentiation.