Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

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to a thousand years. Soil profiles and alluvial sediments in southern Germany’s
Black Forest record several periods of rapid erosion associated with
increased population. Neolithic artifacts in truncated soil profiles show
that initial erosion after the arrival of agriculture about 4000 bc culminated
in extensive soil loss by 2000 bc. Declining cereal pollen and a
period of soil formation characterized a thousand years of lower population
density until renewed erosion in Roman times peaked in the first centuries
ad. A second cycle of agricultural decline, soil formation, and forest
expansion followed until renewed population growth in the Middle Ages
initiated a third, ongoing cycle.
The soils at Frauenberg, a Neolithic site in southeastern Germany,
record erosion of nearly the entire soil profile that began with early Bronze
Age agriculture. Located on a hill that rises three hundred feet inside a
bend in the Danube River, the site’s combination of loess soils and a sweeping
view of the surrounding country appealed to prehistoric farmers. Remnants
of the original soil found in excavations at the site document three
distinct periods of occupation corresponding to Bronze Age farming, a
Roman fort, and a medieval monastery. Radiocarbon dating of charcoal
pulled from soil horizons show that little erosion occurred as soil developed
after deglaciation—until Bronze Age farming exposed clay-rich subsoil
at the ground surface and eroded nearly the entire loess cover. Subsequent
erosion slowed once the less erodible subsoil was exposed. Forest
currently blankets the site, which still has limited agricultural potential.
Evidence from soils, floodplains, and lake sediments at sites across Germany
shows that human impact has been the dominant influence on the
landscape since the last glaciation. Erosion and human occupation occurred
in tandem but not in regional pattern as expected for climate-driven events.
Just as in ancient Greece and around the Mediterranean, central European
cycles of agricultural clearing and erosion associated with population
growth gave way to migration, population decline, and renewed soil
formation.
Surveys of truncated hillslope soils at more than eight hundred sites along
the Rhine River indicate that post-Roman agriculture stripped up to several
feet of soil from hillslopes cleared of native forest. Erosion since ad 600
has been about ten times the erosion rate before forest clearing through erosive
runoff across bare, plowed fields. Similar soil surveys in Luxembourg
report an average of twenty-two inches of lost soil and accelerated soil loss
over more than 90 percent of the landscape. Despite the prevalence of
Neolithic farming on central Europe’s slopes, most of the region’s modern
let them eat colonies