Umbric Epipedon - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 51

Table 6.3 Factors influencing the development of the umbric epipedon
Area Factor References

Climate
Form especially in cool, humid
climates

[This study]

Organisms
CA, PA, WI Grassland vegetation conducive
to umbric

Popenoe et al. ( 1992 ), Waltman and Ciolkosz
( 1995 ) and Quideau and Bockheim ( 1996 )

Umbric common in alpine and
subalpine conifer forests

Richter et al. ( 1989 ) and Follmi et al. ( 2009 )

Relief

NC Restricted drainage leads to

umbric; used to delineate

Vepraskas and Caldwell ( 2008 )

Hydric soils
Parent material
New Zealand Soils derived from volcanic ash
commonly have umbric

Parfitt and Clayden ( 1991 )

Time

PA Present in 2,000-6,000-year-old

soils

Waltman and Ciolkosz ( 1995 )

Italy Form in ~100-500 year Sanesi and Certini ( 2005 )

6.5 Factors Influencing the Distribution of Soils
with Umbric Epipedons

Umbric epipedons form in cool humid climates (Table 6.3 ). Grassland vegetation is
especially conducive to form an umbric epipedon, but they also occur in subalpine
conifer forests. Along with melanic epipedons, umbric epipedons are common on
soils derived from volcanic ash. They form in areas of restricted drainage in many
parts of the country. The umbric epipedon may form in as little as several hundred
years (Waltman and Ciolkosz 1995 ; Sanesi and Certini 2005 ).

6.6 Genesis of Soils with an Umbric Epipedon

The genesis of the umbric epipedon is comparable to that of the mollic epipedon,
except that calcification and base-cation cycling are less significant. Dominant
processes include melanization, cumulization, and bioturbation.

6.7 Summary

Along with the ochric and mollic epipedons, the umbric epipedon is one of the most
commonly epipedons employed in ST. Soil series with an umbric epipedon are
most common in three orders: Inceptisols, Andisols, and Vertisols; they occur to a