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Fig. 18.3 Areas containing soils with ortstein horizons in the conterminous USA and AK
(From Bockheim 2011 )
18.5 Factors Influencing the Distribution of Ortstein
and Placic Horizons
18.5.1 Ortstein
Table 18.5 lists soil-forming factors commonly cited in the literature that favor
ortstein development. Elevation is a key factor distinguishing between soils with
ortstein and geographically related soils without ortstein; in the USA, soils with
some form of ortstein often occur below 200 m elevation (Table 18.6 ). About a third
of the soils occurred in the Great Lakes region on sites with a seasonally high water
table, primarily in the spring following melting of a thick snowpack. In addition,
soils with
50 % ortstein had more restricted drainage than soils with
50 %
>
<
ortstein or soils lacking ortstein in the spodic horizon.
Because rooting depth is restricted in soils with ortstein, the lack of bioturbation
may be important in the development and preservation of an ortstein horizon
(Lapen and Wang 1999 ). Ortstein typically is found in areas with sparse or different
tree cover than in adjacent areas supporting soils without ortstein (Wang
et al. 1978 ). In the Great Lakes region, ortstein occurs in areas containing primarily
northern hardwoods and hemlock but commonly is restricted to specific sites with
red maple ( Acer rubrum ), red pine ( Pinus resinosa ), and other less nutrient
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